Tektronix 2715 User Manual

Download

Service Manual

2715 Spectrum Analyzer Volume 1

070-9096-06

This document supports firmware version

12.01.95 and above.

Warning

The servicing instructions are for use by qualified personnel only. To avoid personal injury, do not perform any servicing unless you are qualified to do so. Refer to all safety summaries prior to performing service.

www.tektronix.com

Tektronix products are covered by U.S. and foreign patents, issued and pending. Information in this publication supercedes that in all previously published material. Specifications and price change privileges reserved.

Tektronix, Inc., P.O. Box 500, Beaverton, OR 97077

TEKTRONIX and TEK are registered trademarks of Tektronix, Inc.

WARRANTY

Tektronix warrants that this product will be free from defects in materials and workmanship for a period of one (1) year from the date of shipment. If any such product proves defective during this warranty period, Tektronix, at its option, either will repair the defective product without charge for parts and labor, or will provide a repl acement in exchange for the defective product.

In order to obtain service under this warranty, Customer must notify Tektronix of the defect before the expiration of t he warranty period and make suitable arrangements for the performance of service. Customer shall be responsible for packaging and shipping the defective product to the service center de signated by Tektronix, with shipping charges prepaid. Tektronix shall pay for the return of the product to Customer i f the shipment is to a location within the country in which the Tektronix service center is located. Custome r shall be responsible for paying all shipping charges, duties, taxes, and any other charges for products returned to any other locations.

This warranty shall not apply to any defect, failure or damage caused by improper use or improper or inadequate maintenance and care. Tektronix shall not be obligated to furnish service under this warranty a) to repair damage resulting from attempts by personnel other than Tektronix representatives to install, repair or service the product; b) to repair damage resulting from improper use or connection to incompatible equipment; or c) to service a product that has been modified or integrated with other products when the effect of such modification or integration increases the time or difficulty of servicing the product.

THIS W ARRANTY IS GIVEN BY TEKTRONIX WITH RESPECT TO THIS PRODUCT IN LIEU OF ANY OTHER WARRANTIES, EXPRESSED OR IMPLIED. TEKTRONIX AND ITS VENDORS DISCLAIM ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. TEKTRONIX’ RESPONSIBILITY TO REPAIR OR REPLACE DEFECTIVE PRODUCTS IS THE SOLE AND EXCLUSIVE REMEDY PROVIDED TO THE CUSTOMER FOR BREACH OF THIS W ARRANTY. TEKTRONIX AND ITS VENDORS WILL NOT BE LIABLE FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES IRRESPECTIVE OF WHETHER TEKTRONIX OR THE VENDOR HAS ADVANCE NOTICE OF THE POSSIBILITY OF SUCH DAMAGES.

Specifications

Operating Information

General Safety Summary ix...................................

Service Safety Summary xi....................................

Preface xv...................................................

Electrical Characteristics 1-1..........................................

Instrument Description 2-1............................................

Conformance to Industry Standards 2-2..................................

Product Service 2-2..................................................

Instrument Construction 2-3...........................................

Installation and Preparation for Use 2-3..................................

Power Cord 2-3.....................................................

Replacing the Fuse 2-4...............................................

Selected Components 2-4.............................................

Assembly and Circuit Numbering 2-4...................................

Accessories 2-4.....................................................

Menus 2-4.........................................................

SWP/TRG Menu Structure 2-6.........................................

UTIL Menu Structure

(1 of 2) 2-7.....................................................

UTIL Menu Structure

(2 of 2) 2-8.....................................................

MRK/FREQ Menu Structure 2-8.......................................

CATV/APPL CATV Measurements Page 1 Menu Structure (1 of 3) 2-9........

CATV/APPL CATV Measurements Page 1 Menu Structure (2 of 3) 2-10........

CATV/APPL CATV Measurements Page 1 Menu Structure (3 of 3) 2-11........

CATV/APPL CATV Measurements Page 2 Menu Structure (1 of 2) 2-12........

CATV/APPL CATV Measurements Page 2 Menu Structure (2 of 2) 2-13........

CATV/APPL Applications Menu Structure 2-14............................

DEMOD Menu Structure 2-14..........................................

DSPL Menu Structure 2-15............................................

USER DEF Menu Structure 2-15........................................

INPUT Menu Structure 2-16...........................................

Theory of Operation

Block Diagram Description 3-1........................................

Center Frequency Control 3-5.........................................

1st LO Buffer 3-7...................................................

Sweep 3-7.........................................................

Display System 3-8..................................................

Circuit Description 3-9........................................

Attenuator and 1st Converter 3-9.......................................

RF Mother Board and Phase Locked 2nd LO 3-12..........................

2715 Spectrum Analyzer Service Manual

Table of Contents

1st LO Interface, 1st LO, and 1st LO Buffer Amplifier 3-14..................

Reference Oscillator 3-16..............................................

Phase Lock Assembly (Center Frequency Control System) 3-21...............

Variable Resolution Module 3-33........................................

RF Options 3-35.....................................................

Log Amplifier 3-38...................................................

Display Storage 3-40..................................................

Microprocessor 3-60..................................................

GPIB, RS-232, Real Time Clock, NVRAM, and Gated Measurement Functions 3-74

Video Demodulator 3-78...............................................

Sweep 3-80.........................................................

Front Panel 3-83.....................................................

Power Supply (Primary and Secondary) 3-87..............................

Power Supply (Display) 3-91...........................................

Performance Verification

Incoming Inspection Test 4-1..........................................

Verification of Tolerance Values 4-1....................................

History Information 4-1..............................................

Equipment Required 4-2..............................................

Power-Up Procedure 4-3..............................................

Front Panel Operation 4-4.............................................

Performance Check Procedure 4-4......................................

Adjustment Procedures

Static Discharge Precautions 5-1.......................................

Recommended Test Equipment 5-2.....................................

Preparation 5-4.....................................................

Adjustments Requiring Flatness Correction 5-4...........................

Instrument Bottom View 5-5..........................................

Adjustments 5-6....................................................

Maintenance

Static Sensitive Components 6-1.......................................

Preventive Maintenance 6-2...........................................

Troubleshooting 6-6.................................................

Cal Debug Flags 6-8.................................................

Corrective Maintenance 6-13...........................................

Assembly Replacement Requiring Flatness Correction 6-17...................

Removing and Replacing Assemblies and Subassemblies 6-17................

Maintenance Adjustments 6-33.........................................

Options Replaceable Electrical Parts Diagrams Replaceable Mechanical Parts

2715 Spectrum Analyzer Service Manual

List of Figures

Table of Contents

Figure 1-1: Typical Accuracy Limits for Carrier-to-Noise

Measurement 1-7..........................................

Figure 1-2: Typical Accuracy Limits for CTB Measurement 1-7......

Figure 1-3: Typical Accuracy Limits for Nongated CSO

Measurement 1-8..........................................

Figure 1-4: Typical Accuracy Limits for Gated CSO

Measurement 1-8..........................................

Figure 1-5: Typical ACL Measurement Limits for 2 dB Accuracy 1-9..

Figure 1-6: Typical D/U Measurement Range Limits for

2 dB Accuracy 1-9.........................................

Figure 1-7: Typical Digital Signal CSO Measurement Range Limit

for 2 dB Accuracy 1-10......................................

Figure 1-8: Typical Digital Signal CTB Measurement Range

Limit for 2 dB Accuracy 1-10.................................

Figure 2-1: 2715 Front Panel Keys 2-5............................

Figure 3-1: Main Block Diagram 3-2.............................

Figure 3-2: Display System Diagram 3-8..........................

Figure 3-3: Attenuator and 1st Converter Diagram 3-10..............

Figure 3-4: Equivalent Circuit for the Bandpass (4 Cavity)

Filter 3-11.................................................

Figure 3-5: Block Diagram of RF Mother Board 3-12................

Figure 3-6: 1st LO Interface and 1st LO Diagram 3-14...............

Figure 3-7: 1st LO Buffer Amplifier Diagram 3-15..................

Figure 3-8: Reference Oscillator Diagram 3-17......................

Figure 3-9: Crystal Heater and 15 V Regulation Circuit 3-18..........

Figure 3-10: Oscillator AC Equivalent 3-19........................

Figure 3-11: Oscillator DC Equivalent 3-20........................

Figure 3-12: Phase Lock Center Frequency Control

Configuration for Wide Spans (Unlocked, Sweep Main Coil) 3-28..

Figure 3-13: Phase Lock Center Frequency Control Configuration

for Moderate Spans (Unlocked, Sweep FM Coil) 3-29.............

Figure 3-14: Phase Lock Center Frequency Control Configuration

for Narrow Spans (Locked, Sweep VCO) 3-30...................

Figure 3-15: Variable Resolution Module Diagram 3-34..............

Figure 3-16: RF Options Diagram 3-36............................

2715 Spectrum Analyzer Service Manual

iii

Table of Contents

Figure 3-17: Timing Diagram for a Typical Write to the Control

Figure 3-18: Timing Diagram of a Typical Sweep for the Horizontal

Tracking A/D Converter 3-51.................................

Figure 3-19: Sequence of Events When Writing Data to the

Waveform Memory 3-54.....................................

Figure 3-20: How a Vertical Scan is Performed 3-56.................

Figure 3-21: The Display of a Single Vector of a Waveform 3-57.......

Figure 3-22: A Single Column of Character Dots 3-57................

Figure 3-23: Vertical Output Integrator 3-58.......................

Figure 3-24: Microprocessor Block Diagram 3-61...................

Figure 3-25: Microprocessor Counter System (CPU) 3-62.............

Figure 3-26: Front Panel Block Diagram 3-83......................

Figure 3-27: How the Debounce Circuit Reacts to Key Closure 3-85....

Figure 3-28: Power Supply Primary Block Diagram 3-88.............

Figure 3-29: Display Amplifiers Block Diagram 3-91................

Figure 4-1: 3rd Order IM Test Setup (25 MHz Separation) 4-17.......

Figure 4-2: Harmonic Distortion Test Equipment Setup 4-18..........

Figure 4-3: 1 dB Compression Point Test Setup 4-20.................

Figure 4-4: Accessory Connector (J103) 4-22.......................

Figure 4-5: Test Equipment Setup for Checking Return Loss 4-28.....

Figure 4-6: Test Signal on Video Line 17 4-32.......................

Figure 4-7: Video Gating Check Waveform (NTSC Illustrated) 4-34....

Figure 4-8: IF Gating Check Waveform (NTSC Illustrated) 4-35......

Figure 5-1: Instrument Bottom View 5-5..........................

Figure 5-2: Display Storage Board Adjustment Locations 5-13........

Figure 5-3: Properly Adjusted Checkerboard Pattern 5-14...........

Figure 5-4: Locked 2nd LO and 5 MHz Bandpass Filter

Adjustments 5-16...........................................

Figure 5-5: Phase Lock CFC Module Adjustment and Test Point

Locations 5-17.............................................

Figure 5-6: Log Board Adjustment and Test Point Locations 5-21.....

Figure 5-7: CAL Level Adjustment on Reference Oscillator Board 5-26.

Figure 5-8: RF Option Adjustment Locations 5-28..................

Figure 5-9: Variable Resolution Module Adjustment Locations 5-29....

Figure 5-10: Flatness adjustment test setup (all instruments

except Option 50) 5-34.......................................

2715 Spectrum Analyzer Service Manual

Table of Contents

Figure 5-1 1: Presetting the Flatness Adjustments on the

Log Board 5-35............................................

Figure 5-12: Gain Step Reference Test Setup 5-36...................

Figure 5-13: Internal Ref Ampltd Test Setup 5-38...................

Figure 5-14: SW410 on the Reference Oscillator Board 5-39..........

Figure 5-15: Adjustment and Test Point Locations on the

Sweep Board 5-41..........................................

Figure 5-16: Typical FM Adjustment Waveform 5-42................

Figure 5-17: HPF Tuning Criteria (at TP110M) 5-45.................

Figure 5-18: Typical Video Waveform 5-48.........................

Figure 5-19: Horizontal Sync Output 5-49.........................

Figure 5-20: Vertical Sync Output Waveform 5-50..................

Figure 5-21: E/O Output Waveform 5-51..........................

Figure 5-22: Test Equipment Characterization Using a Dual

Channel Power Meter for split75 5-59..........................

Figure 5-23: Test Equipment Characterization Using a

Single Channel Power Meter to Characterize the Power Meter

Output for split75 5-59......................................

Figure 5-24: Test Equipment Characterization Using a

Single Channel Power Meter to Characterize the DUT

Output for split75 5-59......................................

Figure 5-25: Test Equipment Characterization Using a Dual

Channel Power Meter for split50 5-60..........................

Figure 5-26: Test Equipment Characterization Using a

Single Channel Power Meter to Characterize the Power Meter

Output for split50 5-60......................................

Figure 5-27: Test Equipment Characterization Using a

Single Channel Power Meter to Characterize the DUT

Output for split50 5-60......................................

Figure 5-28: Flatness Test Setup (75 W) 5-62.......................

Figure 5-29: Flatness Test Setup (50 W) 5-62.......................

Figure 6-1: Main Extender and Secondary Extender 6-4............

Figure 6-2: Signal Steering Square Pins 6-5.......................

Figure 6-3: Surface Mounted Components Lead Configuration 6-14...

Figure 6-4: Top View of Assemblies and RF Deck 6-18...............

Figure 6-5: Assemblies Seen from the Bottom of the Spectrum

Analyzer 6-19..............................................

Figure 6-6: Removing the Front Panel 6-22........................

Figure 6-7: Locations of J510 and J550 on the Phase Lock

Assembly 6-23.............................................

2715 Spectrum Analyzer Service Manual

Table of Contents

Figure 6-8: Connector Locations on the RF Deck 6-24...............

Figure 6-9: RF Deck Screws and Nuts 6-25.........................

Figure 6-10: Fan and Fan Mounting Springs Detail 6-29.............

Figure 6-11: Power Supply Assembly Removal (Bottom View) 6-31....

Figure 6-12: Removing Power Supply Attaching Nuts 6-32...........

Figure 6-13: Location of R602 on the Phase Lock CFC Board 6-34.....

Figure 7-1: Option 15 Installation 7-3............................

Figure 10-1: Cabinet 10-7.......................................

Figure 10-2: Front Panel 10-11....................................

Figure 10-3: Power Supply 10-15..................................

Figure 10-4: Chassis #1 10-18.....................................

Figure 10-5: Chassis #2 10-22.....................................

Figure 10-6: Accessories 10-25....................................

2715 Spectrum Analyzer Service Manual

List of Tables

Table of Contents

T able 1-1: CA TV Characteristics 1-2............................

Table 1-2: Frequency-Related Characteristics 1-11..................

Table 1-3: Frequency/Amplitude Related Characteristics 1-13........

T able 1-4: Amplitude-Related Characteristics 1-14..................

Table 1-5: Input/Output Signal Characteristics 1-17................

Table 1-6: Power Requirements 1-19.............................

Table 1-7: Supplementary Characteristics Due to Options 1-19.......

T able 1-8: General Characteristics 1-20...........................

Table 1-9: Environmental Characteristics 1-21.....................

Table 1-10: Physical Characteristics 1-22.........................

Table 1-11: Certifications and Compliances 1-23....................

Table 1-12: Safety Certification Compliance 1-24...................

Table 1-13: Safety Standards 1-24................................

Table 3-1: Input and Output Bit Definition 3-21....................

Table 3-2: Mode Control Register 1 3-41..........................

Table 3-3: Mode Control Register 2 3-42..........................

T able 3-4: Truth Table for the B,C-Save A Display Screen

Offset 3-43...............................................

T able 3-5: Truth Table for the Acquisition Modes 3-43..............

Table 3-6: Mode Control Register 2 3-43..........................

Table 3-7: Enhanced Mode MKRWFM[3..2] Bit Assignment 3-44.....

Table 3-8: Enhanced Mode MKRWFM[1..0] Bit Assignment 3-45....

Table 3-9: Display Control Register 3-45..........................

Table 3-10: Scroll Register 3-46..................................

Table 3-11: Memory Map for the Display Storage Board 3-48.........

Table 3-12: Control Register Latch and Tristate Buffer

Reference Designators and Microprocessor I/O Port

Address Location 3-49......................................

Table 3-13: Input Conditions Required to Write Either the

Max or Min Accumulators to Waveform Memory 3-53...........

Table 3-14: Page Number/Waveform Relation 3-55.................

Table 3-15: Interrupt Controller Input Connections 3-63............

Table 3-16: Configuration of Jumpers/Wires for Various

Memory IC Sizes 3-65......................................

Table 3-17: Definition of Software Jumpers 3-66....................

2715 Spectrum Analyzer Service Manual

vii

Table of Contents

Table 3-18: Power Supply and Serial Bus Connector (J10)

Signal Names and Definitions 3-68............................

Table 3-19: Microprocessor Interface Connector (J550)

Signal Names and Definitions 3-69............................

T able 3-20: Microprocessor Counter Section Connector

Signal Names and Definitions 3-70............................

Table 3-21: Connectors and Signal Names for the Frequency

Counter Section 3-70.......................................

Table 3-22: Pinout for the 24-Pin DIN Connector (J10) Between the

Microprocessor Board, Power Supply Interconnect,

and Serial I/O 3-71.........................................

Table 3-23: Pinout for the Microprocessor Board Test

Connector (J150) 3-71......................................

Table 3-24: Pinout for the 50 Pin Connector (J550) Between

the Microprocessor, Display Storage, and Digital Options

Boards 3-73...............................................

Table 3-25: Real Time Clock Functions 3-75.......................

Table 4-1: Equipment Required 4-2.............................

Table 4-2: Settings for Shape Factor Check 4-5....................

Table 4-3: Settings for the Noise Sidebands Check 4-7..............

Table 4-4: Front Panel Span Accuracy Settings 4-8................

Table 4-5: Maximum Range in 10 dB/Div 4-11.....................

Table 4-6: Resolution Bandwidth Filter Display Dynamic

Range Settings 4-12........................................

T able 4-7: Sensitivity Settings at 110 MHz 4-13.....................

Table 4-8: Sensitivity Settings at 1800 MHz 4-14....................

T able 4-9: Sensitivity Settings at 2.15 GHz 4-15....................

Table 5-1: Test Equipment 5-2..................................

Table 5-2: Power Supply Tolerances 5-7..........................

Table 5-3: Power Supply Tolerances 5-10..........................

Table 5-4: Correction Bit Values 5-39.............................

Table 5-5: Television Channels 5-40..............................

Table 6-1: Relative Susceptibility to Static Discharge Damage 6-2....

Table 6-2: Cal Debug Messages and Meanings 6-9.................

Table 6-3: Servicing Tools for Boards With Surface

Mounted Components 6-15..................................

viii

2715 Spectrum Analyzer Service Manual

General Safety Summary

Review the following safety precautions to avoid injury and prevent damage to this product or any products connected to it. To avoid potential hazards, use this product only as specified.

Only qualified personnel should perform service procedures.

While using this product, you may need to access other parts of the system. Read the General Safety Summary in other system manuals for warnings and cautions related to operating the system.

ToAvoidFireor

Personal Injury

Use Proper Power Cord. Use only the power cord specified for this product and certified for the country of use.

Connect and Disconnect Properly. Do not connect or disconnect probes or test leads while they are connected to a voltage source.

Ground the Product. This product is grounded through the grounding conductor of the power cord. To avoid electric shock, the grounding conductor must be connected to earth ground. Before making connections to the input or output terminals of the product, ensure that the product is properly grounded.

Observe All Terminal Ratings. To avoid fire or shock hazard, observe all ratings and marking on the product. Consult the product manual for further ratings information before making connections to the product.

The common terminal is at ground potential. Do not connect the common terminal to elevated voltages.

Do not apply a potential to any terminal, including the common terminal, that exceeds the maximum rating of that terminal.

Do Not Operate Without Covers. Do not operate this product with covers or panels removed.

Use Proper Fuse. Use only the fuse type and rating specified for this product.

Avoid Exposed Circuitry. Do not touch exposed connections and components

when power is present.

Wear Eye Protection. Wear eye protection if exposure to high-intensity rays or laser radiation exists.

Do Not Operate With Suspected Failures. If you suspect there is damage to this product, have it inspected by qualified service personnel.

Do Not Operate in Wet/Damp Conditions.

Do Not Operate in an Explosive Atmosphere.

2715 Spectrum Analyzer Service Manual

General Safety Summary

Keep Product Surfaces Clean and Dry.

Provide Proper Ventilation. Refer to the manual’s installation instructions for

details on installing the product so it has proper ventilation.

Symbols and Terms

Terms in this Manual. These terms may appear in this manual:

WARNING. Warning statements identify conditions or practices that could result in injury or loss of life.

CAUTION. Caution statements identify conditions or practices that could result in damage to this product or other property.

Terms on the Product. These terms may appear on the product:

DANGER indicates an injury hazard immediately accessible as you read the marking.

WARNING indicates an injury hazard not immediately accessible as you read the marking.

CAUTION indicates a hazard to property including the product.

Symbols on the Product. The following symbols may appear on the product:

WARNING

High Voltage

Protective Ground

(Earth) Terminal

CAUTION

Refer to Manual

Double

Insulated

2715 Spectrum Analyzer Service Manual

Service Safety Summary

Only qualified personnel should perform service procedures. Read this Service Safety Summary and the General Safety Summary before performing any service

procedures.

Do Not Service Alone. Do not perform internal service or adjustments of this product unless another person capable of rendering first aid and resuscitation is present.

Disconnect Power. To avoid electric shock, switch off the instrument power, then disconnect the power cord from the mains power.

Use Caution When Servicing the CRT. To avoid electric shock or injury, use extreme caution when handling the CRT. Only qualified personnel familiar with CRT servicing procedures and precautions should remove or install the CRT.

CRTs retain hazardous voltages for long periods of time after power is turned off. Before attempting any servicing, discharge the CRT by shorting the anode to chassis ground. When discharging the CRT, connect the discharge path to ground and then the anode. Rough handling may cause the CRT to implode. Do not nick or scratch the glass or subject it to undue pressure when removing or installing it. When handling the CRT, wear safety goggles and heavy gloves for protection.

Use Care When Servicing With Power On. Dangerous voltages or currents may exist in this product. Disconnect power, remove battery (if applicable), and disconnect test leads before removing protective panels, soldering, or replacing components.

To avoid electric shock, do not touch exposed connections.

X-Radiation. To avoid x-radiation exposure, do not modify or otherwise alter the high-voltage circuitry or the CRT enclosure. X-ray emissions generated within this product have been sufficiently shielded.

2715 Spectrum Analyzer Service Manual

Service Safety Summary

xii

2715 Spectrum Analyzer Service Manual

Preface

This manual contains service information for the 2715 Spectrum Analyzer. The service information is located in two volumes. Volume 1 contains the maintenance procedures and parts lists. Volume 2 contains the component locators and schematic diagrams.

This manual is divided into the following sections.

H Section 1: Specifications, contains characteristic tables detailing Electrical

Characteristics, Mechanical Characteristics, and Environmental Character-

istics.

H Section 2: Operating Information, contains information on how to install and

operate the product.

H Section 3: Theory of Operation, contains both a general and detailed circuit

description of the various modules that make up the instrument.

H Section 4: Performance Verification, is a procedure to ensure, when passed,

that the product operates properly and meets its advertised performance

levels.

H Section 5: Adjustment Procedures, is a procedure to ensure that, when

performed, the product can meet the performance levels for characteristics

listed in Section 1, Specifications.

H Section 6: Maintenance, contains instructions for removal and replacement

of internal modules or components.

H Section 7: Options, describes all options available for this instrument.

H Section 8: Replaceable Electrical Parts, is a list of replaceable assemblies

and electrical components.

H Section 9: Diagrams, Refer to the 2715 Spectrum Analyzer Service Manual

Volume 2.

H Section 10: Replaceable Mechanical Parts, is a list of replaceable assemblies

and mechanical components. Exploded-view illustrations are included to

relate assemblies to the parts list.

The following manuals are also available for the 2715 Spectrum Analyzer.

H 2715 User Manual provides information necessary to operate the 2715

Spectrum Analyzer.

H 2714 & 2715 Programmer Manual includes all GPIB commands, queries,

and responses for the instrument.

H The Cable TV RF Measurement Software Manual describes how to use the

Cable TR RF Measurements Software, a test system that measures cable TV

parameters.

2715 Spectrum Analyzer Service Manual

xiii

Preface

Contacting Tektronix

Phone 1-800-833-9200*

Address Tektronix, Inc.

Department or name (if known) 14200 SW Karl Braun Drive P.O. Box 500 Beaverton, OR 97077 USA

Web site www.tektronix.com

Sales support 1-800-833-9200, select option 1*

Service support 1-800-833-9200, select option 2*

Technical support Email: techsupport@tektronix.com

1-800-833-9200, select option 3*

6:00 a.m. -- 5:00 p.m. Pacific time

* This phone number is toll free in North America. After office hours, please leave a

voice mail message. Outside North America, contact a Tektronix sales office or distributor; see the Tektronix web site for a list of offices.

xiv

2715 Spectrum Analyzer Service Manual

Specifications

This section lists the electrical, physical, and environmental characteristics of the spectrum analyzer, specifies the performance requirements for those characteristics, and provides supplementary information.

Electrical Characteristics

Unless otherwise stated, the following tables of electrical characteristics and features apply to the spectrum analyzer after a 15 minute warm-up period (within the environmental limits) and after all normalization procedures have been carried out.

Information in the Performance Requirement column of Tables 1--2 through 1--8 is guaranteed and verifiable unless otherwise noted. Supplemental Information is intended to further explain a characteristic, its performance requirement, or to describe characteristic performance that is impractical to verify. Supplemental Information is not guaranteed and may not be supported by a performance check procedure.

Changes to a characteristic because of the addition of an option are included in Table 1--7.

2715 Spectrum Analyzer Service Manual

1- 1

Specifications

Table 1- 1: CATV Characteristics

Characteristic Description

Input Configuration

All except Option 50 75 Ω Female F connector

Option 50 50 Ω Type N connector

Channel Selection The visual and aural carriers are displayed when the channel number is entered, or

either [ y ] or [ b ] next to [CHAN/FREQ] is pressed

Tune Configuration STD (73.603), HRC (73.605), IRC (73.612), and Custom

Channel Range 0to999

Frequency Range (except Opt 50 and Opt 75)

Frequency Range (Opt 50 and Opt 75)

Visual Carrier Frequency Measurement

Method Internal Counter

Resolution 1Hz

Accuracy 5 × 10-7× Carrier Frequency ±10 Hz, ±1 Least Significant Digit

1MHzto1.8GHz2, Preamp limited to 600 MHz

1 MHz to 2.15 GHz2, Preamp limited to 600 MHz

Accuracy is dependent on the accuracy of the spectrum analyzer — see Frequency Accuracy in Table 1--2.

@ 55.25 MHz (Ch 2) worst case is ±38 Hz @ 325.25 MHz (Ch 41) worst case is ±173 Hz @ 643.25 MHz (Ch 94) worst case is ±332 Hz

Visual-to-Aural Carrier Frequency Measurement Aural carrier measured relative to the visual carrier

Method Internal Counter

Difference Range 1 MHz to 10 MHz3for an amplitude difference of ≤30 dB and aural C/N ≥15 dB

(300 kHz RBW)

Resolution 1Hz

Accuracy ±15 Hz for visual-to-aural carrier difference ≤8MHz

Visual Carrier Peak Level Measurement Absol ute peak amplitude of visual carrier measured with PREAMP OFF

Accurate Frequency and Amplitude

Visual carrier frequency measurement Visual-to-aural carrier frequency measurement Visual carrier peak level measurement Visual-to-aural carrier level difference measurement

Accurate Amplitude Only Visual carrier peak level measurement

Visual-to-aural carrier level difference measurement

Fast Amplitude Only Carrier amplitudes are measured using marker values in 10 dB/div vertical scale

Amplitude Range --18 dBmV to +58.8 dBmV4for visual C/N ≥30 dB (300 kHz RBW)

Configured using Cable TV RF Measurements Software.

Dependent on selected channel table. Frequencies above 1.8 GHz are not supported by the Cable TV RF Measurements Software.

Dependent on selected channel table.

Total input power (all signals included) cannot exceed +70 dBmV.

1- 2

2715 Spectrum Analyzer Service Manual

Specifications

Table 1- 1: CATV Characteristics (Cont.)

Characteristic Description

Frequency Range 15 to 1015 MHz

Resolution 0.1 dB

Absolute Accuracy ±2.5 dB for visual C/N ≥30 dB (300 kHz RBW) and for FM signal C/N ≥33 dB (100

kHz RBW) assumes flatness corrections are present

Relative Accuracy ±0.5 dB relative to adjacent channel

±1.2 dB relative to all other channels

Visual-to-Aural Carrier Level Difference Measurement

Difference Range 0 to 30 dB for aural C/N ≥15 dB (300 kHz RBW)

Resolution 0.1 dB

Accuracy ±0.75 dB for aural C/N ≥15 dB (300 kHz RBW)

Averaged Power (Typical) Averaged amplitude measured with preamp off

Accuracy ±2.5 dB for input levels above --30 dBmV, up to +37 dBmV (multichannel) or

Resolution 0.1 dB

Modulation Depth Measurement (Typical)

AM Range 50% to 95%

Resolution 0.1%

Accuracy ±2% for visual C/N ≥40 dB (300 kHz RBW)

HUM/LFD Measurement (Typical) Power line frequency is measured on an unmodulated visual carrier, and low

AM Range 1% to 10% peak-to-peak

Resolution 0.1%

Accuracy ±1% for Hum ≤5% and visual C/N ≥25 dB (300 kHz RBW)

Carrier-to-Noise (C/N) Measurement (Typical)

Optimum Input Range See Figure 1--1 on page 1--7

Maximum Range See Figure 1--1 on page 1--7

Resolution 0.3 dB

Accuracy See Figure 1--1 on page 1--7

In-Service C/N (typical) Noise density is measured at 2 MHz offset (by default) from visual carrier during

Optimum Input Range See Figure 1--1 on page 1--7

Maximum Range See Figure 1--1 on page 1--7

Resolution 0.3 dB

Aural carrier level measured relative to the visual carrier

+52 dBmV (preselector in use)

Percent AM measured from sync tip to lowest white level found in 10 sweeps (the VITS line is used if it is defined in the channel table)

frequency disturbance (LFD) is measured on the modulated carrier

±2% for Hum <10% and visual C/N ≥25 dB (300 kHz RBW)

Default noise floor is a normalized 4 MHz bandwidth measured relative to the visual carrier peak

quiet lines in the vertical interval, then normalized to 4 MHz BW and expressed as dBc

2715 Spectrum Analyzer Service Manual

1- 3

Specifications

Table 1- 1: CATV Characteristics (Cont.)

Characteristic Description

Accuracy See Figure 1--1 on page 1--7

Desired-to-Undesired Ratio (Typical) Channel averaged power is divided by total noise plus distortion in the channel

Resolution 0.1 dB

Accuracy ±2 dB within the limits shown in Figure 1--6 on page 1--9

CTB Measurement (Typical) Composite triple beat (CTB) is measured relative to the visual carrier peak according

to the NCTA recommended spectrum analyzer settings — SINGLE-SWEEP mode does not use all the NCTA recommended settings

Maximum Range See Figure 1--2 on page 1--7

Resolution 0.3 dB

Accuracy See Figure 1--2 on page 1--7

Digital Channel CTB (Typical) Measured relative to the averaged power of the test channel

Resolution 0.3 dB

Accuracy ±2 dB within the limits shown in Figure 1 --8 on page 1 --10

CSO Measurement (Typical)

Optimum Input Range See Figure 1--3 on page 1--8

Maximum Range See Figure 1--3 on page 1--8

Resolution 0.3 dB

Accuracy See Figure 1--3 on page 1--8

In-Service CSO (Typical) CSO products are measured per NCTA recommendations during quiet lines in the

Optimum Input Range See Figure 1--4 on page 1--8

Maximum Range See Figure 1--4 on page 1--8

Resolution 0.3 dB

Accuracy See Figure 1--4 on page 1--8

Digital Channel CSO (Typical) Measured relative to the averaged power of the test channel

Resolution 0.3 dB

Accuracy ±2.0 dB within the limits shown in Figure 1 --7 on page 1--10

Frequency Response Measurement (Typical)

Reference Trace Storage (Nonvolatile)

Range 5 dB/div, fixed

Resolution 0.2 dB

Trace Flatness Accuracy ±0.75 dB

Composite second order (CSO) is measured relative to the visual carrier peak according to the NCTA recommended spectrum analyzer settings — SINGLESWEEP and CONTINUOUS modes do not use all the NCTA recommended settings

vertical interval, then expressed as dBc

For fixed-amplitude scrambling or no scrambling, system amplitude variations (flatness) are measured relative to a reference trace (stored during the frequency response reference setup)

Up to 10 traces with spectrum analyzer states

1- 4

2715 Spectrum Analyzer Service Manual

Specifications

Table 1- 1: CATV Characteristics (Cont.)

Characteristic Description

Carrier Survey Absolute peak amplitude of each visual carrier measured and each associated aural

carrier level measured relative to the measured visual carrier for the selected channels — characteristics are identical to the frequency (visual and aural) and level measurements (frequency is counted only if ACCURATE FREQUENCY AND AMPL is on)

Accurate Frequency and Amplitude

Accurate Amplitude Only Visual carrier peak level measurement

Fast Amplitude Only Carrier amplitudes are measured using marker values in 10 dB/div vertical scale

Visual Carrier

Amplitude Range --18 dBmV to +58.8 dBmV5for C/N ≤30 dB (300 kHz RBW)

Frequency Range 15 MHz to 1015 MHz

Resolution 0.3 dB

Absolute Accuracy ±2.7 dB for visual C/N ≥30 dB (300 kHz RBW) and for FM signal C/N ≥33 dB (100

Relative Accuracy ±0.8 dB relative to adjacent channel

Aural Carrier

Difference Range 0to30dBforC/N≥15 dB (300 kHz RBW)

Resolution 0.3 dB

Accuracy ±1.1 dB for C/N ≥15 dB (300 kHz RBW)

Aural <FM> Deviation (Typical) Peak FM deviation measured for the selected channel

Range 10 kHz to 50 kHz, usable to 80 kHz

Accuracy ±4 kHz

Cross Modulation (Typical) The third order distortion at the horizontal sync frequency (AM) measured on the

Range 48 dB

Resolution 0.1 dB

Accuracy ±2 dB for cross modulation <36 dB

Listen (Typical) The aural carrier for the selected channel is demodulated

Output Speaker or headphones with volume control

Demodulation Type FM

Sweep Displays instantaneous peak FM deviation

Total input power (all signals included) cannot exceed +70 dBmV.

Visual carrier frequency measurement Visual-to-aural carrier frequency measurement Visual carrier peak level measurement Visual-to-aural carrier level difference measurement

Visual-to-aural carrier level difference measurement

kHz RBW) assumes flatness corrections are present

±1.5 dB relative to all other channels

unmodulated visual carrier, as corrected to the NCTA recommended synchronous square wave modulation procedure

±3 dB for cross modulation <48 dB

2715 Spectrum Analyzer Service Manual

1- 5

Specifications

Table 1- 1: CATV Characteristics (Cont.)

Characteristic Description

View Picture (Typical) The visual carrier, NTSC or PAL format depending on the selected channel, is

demodulated

View Modulation (Field) (Typical) One video field of the selected channel video is displayed

View Modulation (Line) (Typical) The VITS line is displayed — if no VITS line is specified in the channel table, line 17

is displayed

TV Line Selection Selectable using the FREQ/M KRS knob during View Line Modulation function

Line Format NTSC or PAL

Line Range 1 to 525 (NTSC), 1 to 625 (PAL)

Sweep Time 10 s/div

In-Channel Response

Range ±3 dB (the auto test is run in 1 dB/div)

Resolution 0.1 dB

Accuracy ±0.5 dB, Auto mode

±0.8 dB, Interactive mode

Adjacent Channel Leakage (Typical) Averaged power in adjacent channel(s) is divided by averaged power for the test

channel

Resolution 0.1 dB

Accuracy ±2.0 dB within limits shown in Figure 1--5 on page 1--9

In-Service In-Channel Response (Typical) Standard vertical interval test signal (line sweep, ghost-canceller, multiburst) is

measured within gate which excludes active video; result is expressed as dB P-P

Resolution 0.2 dB

Accuracy ± 0.5 dB assuming test signal is flat at head end

1- 6

2715 Spectrum Analyzer Service Manual

-- 9 0

-- 8 0

-- 7 0

Specifications

-- 6 0

Measurement

Minimum C/N

measurements

C/N

Limit (dBc)

for gated

-- 5 0

-- 4 0

-- 3 0

-- 2 0

-- 1 0

Minimum signal level for gated measurement (at 1000 MHz)

Minimum signal level for gated measurement (to 500 MHz)

-- 2 0

-- 3 0

--100 102030 4050 6070

VISUAL CARRIER PEAK (dBmV)

Figure 1- 1: Typical Accuracy Limits for Carrier-to-Noise Measurement

-- 9 0

-- 8 0

-- 7 0

± 4dBto500MHz

± 2dBto500MHz ± 4 dB at 1000 MHz ± 2 dB at 1000 MHz

Note: 60 channel flat system

± 4dBto500MHz(Note1) ± 2dBto500MHz(Note1)

-- 6 0

CTB

Measurement

Limit (dBc)

-- 5 0

-- 4 0

-- 3 0

-- 2 0

-- 1 0

Minimum signal level for gated measurement (at 1000 MHz)

Minimum signal level for gated measurement (to 500 MHz)

-- 2 0

-- 3 0

--100 102030 4050 6070

VISUAL CARRIER PEAK (dBmV)

Figure 1- 2: Typical Accuracy Limits for CTB Measurem ent

2715 Spectrum Analyzer Service Manual

± 4dBto500MHz(Note2) ± 2dBto500MHz(Note2)

± 4 dB at 1000 MHz (Note 2) ± 2 dB at 1000 MHz (Note 2)

Note 1 Approximate extended limits if preselector is used and mixer input level is set to --20 dBm.

Note 2 Normal limits without preselector and mixer input level set to default setting of --30 dBm in a 60 channel flat system.

1- 7

Specifications

-- 9 0

-- 8 0

-- 7 0

-- 6 0

CSO

Measurement

Limit (dBc)

-- 5 0

-- 4 0

-- 3 0

-- 2 0

-- 1 0

Minimum signal level for gated measurement (at 1000 MHz)

Minimum signal level for gated measurement (to 500 MHz)

-- 2 0

-- 3 0

--100 102030 40506070

VISUAL CARRIER PEAK (dBmV)

Figure 1- 3: Typical Accuracy Limits for Nongated CSO Measurement

-- 9 0

-- 8 0

-- 7 0

± 4dBto500MHz(Note1)

± 2dBto500MHz(Note1)

± 4dBto500MHz(Note2) ± 2dBto500MHz(Note2) ± 4 dB at 1000 MHz (Note 2) ± 2 dB at 1000 MHz (Note 2)

Note 1 Approximate extended limits if preselector is used and mixer input level is set to --20 dBm.

Note 2 Normal limits without preselector and mixer input level set to default setting of --30 dBm. in a 60 channel flat system

-- 6 0

CSO

Measurement

Limit (dBc)

-- 5 0

-- 4 0

-- 3 0

-- 2 0

-- 1 0

Minimum signal level for gated measurement (at 1000 MHz)

Minimum signal level for gated measurement (to 500 MHz)

-- 2 0

-- 3 0

--100 102030 40506070

VISUAL CARRIER PEAK (dBmV)

Figure 1- 4: Typical Accuracy Limits for Gated CSO Measurement

1- 8

± 4dBto500MHz(Note1)

± 2dBto500MHz(Note1)

± 4dBto500MHz(Note2) ± 2dBto500MHz(Note2) ± 4 dB at 1000 MHz (Note 2) ± 2 dB at 1000 MHz (Note 2)

Note 1 Approximate extended limits if preselector is used and mixer input level is set to --20 dBm.

Note 2 Normal limits without preselector and mixer input level set to default setting of --30 dBm in a 60 channel flat system.

2715 Spectrum Analyzer Service Manual

-- 6 5

-- 5 5

Specifications

To 500 MHz

500 MHz to 1000 MHz

Measurement

Limit (dBc)

-- 4 5

-- 3 5

-- 2 5

-- 2 0

--10 0 1020 30 40 506070

INPUT LEVEL (dBmV) FOR SINGLE-SIGNAL TEST ENVIRONMENT

Figure 1- 5: Typical ACL Measurement Limits for 2 dB Accuracy

To 500 MHz using preselector

500 MHz to 1000 MHz using preselector

To 500 MHz in 60-channel flat system dominated by analog signals 10 dB stronger than average power of channel under test

500 MHz to 1000 MHz in 60-channel flat system dominated by analog signals 10 dB stronger than average power of channel under test

Measurement

Limit (dB)

-- 2 0

--10 0 1020 30 40 506070

CHANNEL UNDER TEST INPUT LEVEL (dBmV)

Figure 1- 6: Typical D/U Measurement Range Limits for 2 dB Accuracy

2715 Spectrum Analyzer Service Manual

1- 9

Specifications

To 500 MHz using preselector

500 MHz to 1000 MHz using preselector

To 500 MHz in 60-channel flat system dominated by analog signals 10 dB stronger than average power of channel under test

500 MHz to 1000 MHz in 60-channel flat system dominated by analog signals 10 dB stronger than average power of channel under test

-- 6 5

-- 5 5

Measurement

Limit (dBc)

-- 4 5

-- 3 5

-- 2 5

-- 2 0

--10 0 1020 30 40 506070

INPUT LEVEL (dBmV)

Figure 1- 7: Typical Digital Signal CSO Measurement Range Limit for 2 dB Accuracy

To 500 MHz using preselector

500 MHz to 1000 MHz using preselector

To 500 MHz in 60-channel flat system dominated by analog signals 10 dB stronger than average power of channel under test

500 MHz to 1000 MHz in 60-channel flat system dominated by analog signals 10 dB stronger than average power of channel under test

-- 6 5

-- 5 5

Measurement

Limit (dBc)

-- 4 5

-- 3 5

-- 2 5

-- 2 0

--10 0 1020 30 40 506070

INPUT LEVEL (dBmV)

Figure 1- 8: Typical Digital Signal CTB Measurement Range Limit for 2 dB Accuracy

1- 10

2715 Spectrum Analyzer Service Manual

Specifications

Table 1- 2: Frequency-Related Characteristics

Characteristic Performance Requirement Supplemental Information

Channel Tuned with keypad, [CHAN/FREQ] [ y ],

or [CHAN/FREQ] [ b ],accordingtothe selected channel table

Frequency

Range All except Option 50 and Option 75:

9 kHz to 1.8 GHz Option 50 and Option 75: 9 kHz to

2.15 GHz

Accuracy 5 × 10

Drift

Long Term (One Year) ±2 PPM/year

Short Term (SPAN/DIV ≤20 kHz) All except Option 50 and Option 75:

Readout Resolution 1 kHz or 1 Hz (counter readout), menu

Frequency Span/Div

Range Using

Accuracy/Linearity Within 3% Measured over the center 8 divisions

Flatness (Relative to the Reference Level at 100 MHz)

-- 7

of center frequency ±10 Hz ±1

least significant digit

≤400 Hz up to 1.8 GHz Option 50 and Option 75: 500 Hz above

1.8 GHz

All instruments: ±2dB9KHzto1.8GHz Option 50 and Option 75: ±3 dB above

1.8 GHz

Tuned with keypad, [CHAN/FREQ] [ y ], [CHAN/FREQ] [ b ], FREQ/MARKERS knob, UTIL menu, or MKR/FREQ menu

Assumes zero drift since last normalization procedure

With frequency corrections enabled

selectable

[SPAN/DIV] [ y ] and [SPAN/DIV] [ b ] buttons, selections in a 1--2--5 sequence Using the keypad or UTIL menu, select any value from 100 MHz/div to 1 kHz/div. In MAXSPAN, 180 MHz/div (All except Option 50 and Option 75) or 215 MHz/div (Option 50 and Option 75) In ZERO SPAN, 0 Hz/div

Measured with 10 dB of RF Attenuation and PREAMP off

Flatness is affected by: H Input voltage standing-wave ratio

(VSWR)

H Gain variation H Mixer conversion

2715 Spectrum Analyzer Service Manual

1- 11

Specifications

Table 1- 2: Frequency-Related Characteristics (Cont.)

Characteristic Supplemental InformationPerformance Requirement

Residual FM

With SPAN/DIV ≤20 kHz All except Option 50 and Option 75:

≤100 Hz peak-to-peak total excursion in 20 ms up to 1.8 GHz Option 50 and Option 75: ≤120 Hz peak-to-peak total excursion in 20 ms (above 1.8 GHz)

With SPAN/DIV >20 kHz All except Option 50 and Option 75:

≤2 kHz peak-to-peak total excursion in 20 ms up to 1.8 GHz Option 50 and Option 75: ≤2.4 KHz peak-to-peak total excursion in 20 ms above 1.8 GHz

Resolution Bandwidth (6 dB down) Resolution bandwidth selections are:

Shape Factor (60 dB/6 dB) 7:1 or less for all resolution bandwidths

≤1MHz

Noise Sidebands All except Option 50 and Option 75:

≤--70 dBc at 30X Resolution Bandwidth for all resolution bandwidths ≤100 kHz Option 50 and Option 75: ≤–69 dBc at 30X Resolution Bandwidth for all resolution bandwidths ≤100 kHz

Video Filter Reduces video bandwidth to about 1% of

Short term, after 1 hr warm-up, and with PHASELOCK in AUTO mode

5 MHz, 1 MHz, 300 kHz, 100 kHz, 30 kHz, 10 kHz, 3 kHz, 1 kHz, and 300 Hz for the spectrum analyzer

the selected resolution bandwidth; or one of 12 video filters (3 Hz, 10 Hz, 30 Hz, 100 Hz, 300 Hz, 1 kHz, 3 kHz, 10 kHz, 30 kHz, 100 kHz, 300 kHz, or WIDE) can be selected from the UTIL menu

1- 12

2715 Spectrum Analyzer Service Manual

Specifications

Table 1- 2: Frequency-Related Characteristics (Cont.)

Characteristic Supplemental InformationPerformance Requirement

Resolution Bandwidth (6 dB down) Resolution bandwidth selections are:

5 MHz, 1 MHz, 300 kHz, 100 kHz, 30 kHz, 10 kHz, 3 kHz, 1 kHz, and 300 Hz for the spectrum analyzer

Shape Factor (60 dB/6 dB) 7:1 or less for all resolution bandwidths

≤1MHz

Noise Sidebands ≤--70 dBc at 30X Resolution Bandwidth

for all resolution bandwidths ≤100 kHz

Video Filter Reduces video bandwidth to about 1% of

the selected resolution bandwidth; or one of 12 video filters (3 Hz, 10 Hz, 30 Hz, 100 Hz, 300 Hz, 1 kHz, 3 kHz, 10 kHz, 30 kHz, 100 kHz, 300 kHz, or WIDE) can be selected from the UTIL menu

Table 1- 3: Frequency/Amplitude Related Characteristics

Characteristic Performance Requirement Supplemental Information

Marker The frequency and amplitude values of

the marker position are displayed and are preceded by the letter M

[MKR] [ ' ] and [MKR] [ a ] position the marker to the next right or left signal peak, respectively

Accuracy

Frequency Same as SPAN/DIV

Amplitude A function of the reference level, vertical

scale factor, and normalizations (see Display Dynamic Range on page 1--15)

Also, flatness corrections while in CATV mode for range of 15 MHz to 1.105 GHz

Delta Marker When activated, a second marker is

displayed at the same frequency as the first marker. This is the “Reference Marker”

Accuracy

Frequency 1 PPM ±10 Hz of the higher marker

frequency

Amplitude Same as Marker

The FREQ/MARKERS control may be used to position the first marker; the frequency and amplitude differences between markers are readouts preceded by the letter D

With both signals counted

2715 Spectrum Analyzer Service Manual

1- 13

Specifications

Table 1- 3: Frequency/Amplitude Related Characteristics (Cont.)

Characteristic Supplemental InformationPerformance Requirement

Center Measure When activated, the signal nearest

center screen (or nearest marker if marker is on) and above a preset threshold level, is moved to center screen

The frequency and amplitude values are preceded by the letter C

Readout Resolution 1 kHz or 1 Hz Readout resolution is selectable

Signal Tracking When activated, the centered signal is

held at center screen

Signal tracking requires a signal strength greater than the threshold level

If the strength of a signal being tracked decreases below the threshold level, the instrument displays the message NO SIGNAL FOUND ABOVE THRESHOLD

Table 1- 4: Amplitude-Related Characteristics

Characteristic Performance Requirement Supplemental Information

Vertical Display Mode 10 dB/div, 5 dB/div, 1 dB/div, and Linear

Reference Level

Range Top of g r a t icul e

Log Mode --21.2 dBmV to +68.8 dBmV

(--41.2dBmVto+48.8dBmVwiththe PREAMP enabled)

Linear Mode 10.83 V/div to 342.33 mV/div

(1.08 nV div to 34.23 mV/div with the PREAMP enabled)

Steps

Log Mode 1dBor10dB

Linear Mode 1--2--5 sequence: 10.83 V/div to

342.33 mV/div

FINE REF LVL STEP Activated ≥0.2 division per increment

Accuracy Dependent on:

H Normalizations H Calibrator accuracy H Frequency response

1- 14

2715 Spectrum Analyzer Service Manual

Table 1- 4: Amplitude-Related Characteristics (Cont.)

Characteristic Supplemental InformationPerformance Requirement

Specifications

Display Dynamic Range

Accuracy

10 dB/div Mode ±1.0 dB/10 dB to a maximum cumulative

5 dB/div Mode ±1.0 dB/10 dB to a maximum cumulative

1 dB/div Mode ±1 dB m aximum error over the 8 dB range

Linear Mode ±5% of full scale

RF Attenuator Range 0to50dBin2dBsteps

All except Option 50 and Option 75: 80 dB maximum (Log) 8 divisions (Linear)

error of ±2.0 dB over the 70 dB range and a maximum cumulative error of ±4.0 dB over the 80 dB range

error of ±2.0 dB over the 40 dB range

Log Mode Display Dynamic Range is dependent upon the selected Resolution Bandwidth.

The accuracy specifications apply for amplitude measurements done with the marker only, since marker measurements are corrected for logging errors.

Option 50 and Option 75: Baseline will rise to indicated value, typically 10 dB to 20 dB below signal level applied near frequency of

2.11 GHz. Display Dynamic Range is reduced if there is signal energy at or near

2.11 GHz.

10 dB/div accuracy and range is affected by the signal-to-noise ratio of the selected Resolution Bandwidth filter. See following table for maximum specified range.

Resolution Bandwidth dB Down

5MHz 40

1MHz 40 300 kHz 50 100 kHz 50

30 kHz 60 10 kHz 60

3 kHz 80

1 kHz 80 300 Hz 80

2715 Spectrum Analyzer Service Manual

1- 15

Specifications

1.8GHzrefertotheOption50and

Abov

fromapproximately10MHzto9kHz.

600MHz.

Table 1- 4: Amplitude-Related Characteristics (Cont.)

Characteristic Supplemental InformationPerformance Requirement

Sensitivity without Preamp Equivalent maximum input noise for

Resolution Bandwidth @110 MHz @ 1.8 GHz @ 2.15 GHz*

5MHz --36 dBmV --28 dBmV –26 dBmV

(--85 dBm) (--77 dBm) –75 dBm)

1MHz --43 dBmV --35 dBmV –33 dBmV

(--92 dBm) (--84 dBm) –82 dBm)

300 kHz --48 dBmV --40 dBmV –38 dBmV

(--97 dBm) (--89 dBm) –87 dBm)

100 kHz --53 dBmV --45 dBmV –43 dBmV

(--102 dBm) (--94 dBm) –92 dBm)

30 kHz --58 dBmV --50 dBmV –48 dBmV

(--107 dBm) (--99 dBm) –97 dBm)

10 kHz --63 dBmV --55 dBmV –53 dBmV

(--112 dBm) (--104 dBm) –102 dBm)

3 kHz --68 dBmV --60 dBmV –58 dBmV

(--117 dBm) (--109 dBm) –107 dBm)

1 kHz --73 dBmV --65 dBmV –63 dBmV

(--122 dBm) (--114 dBm) –112 dBm)

300 Hz --78 dBmV --70 dBmV –68 dBmV

(--127 dBm) (--119 dBm) –117 dBm)

Sensitivity with Preamp NOTE. Sensitivity with the Preamp

Resolution Bandwidth @110 MHz @ 1.8 GHz and 2.15 GHz

5MHz --48 dBmV Not Specified

(--95 dBm)

1MHz --55 dBmV Not Specified

(--104 dBm)

300 kHz --60 dBmV Not Specified

(--109 dBm)

100 kHz --65 dBmV Not Specified

(--114 dBm)

30 kHz --70 dBmV Not Specified

(--119 dBm)

10 kHz --75 dBmV Not Specified

(--124 dBm)

3 kHz --80 dBmV Not Specified

(--129 dBm)

1 kHz --85 dBmV Not Specified

(--134 dBm)

300 Hz --90 dBmV Not Specified

(--139 dBm)

each resolution bandwidth.

*Performance measurements above

1.8 GHz refer to the Option 50 and Option 75 instruments only.

Sensitivity decreases linearly approximately 8 dB from 9 KHz to 1.8 GHz.

e 1.8 GHz sensitivitydecreases

linearly approximately 10 dB.

NOTE: Sensitivity degrades as the FREQUENCY setting is decreased

Maximum loss in sensitivity is approximately 20 dB.

enabled is not specified above

1- 16

2715 Spectrum Analyzer Service Manual

Specifications

Table 1- 4: Amplitude-Related Characteristics (Cont.)

Characteristic Supplemental InformationPerformance Requirement

Spurious Responses

Residual (no input signal) All except Option 50 and Option 75:

≤ --51 dBmV (≤--100 dBm) except at 1780 MHz where the spurious response is ≤--41 dBmV (≤--90 dBm). Option 50 and Option 75: ≤--26 dBmV (≤--75 dBm) at 2.0 GHz.

3rdOrder IM (Intermodulation) Products All except Option 50 and Option 75: ≤-- 7 0

dBcupto1.8GHz

Zero Frequency Spur ≤+39 dBmV (≤--10 dBm) Referenced to input with 0 dB RF

2ndHarmonic Distortion ≤--66 dBc Measured with 1stmixer input level of

LO (Local Oscillator) Emission All except Option 50 and Option 75: ≤ -- 7 0

≤--21 dBmV (≤--70 dBm)

With 0 dB RF attenuation

From any two on-screen signals within any frequency span Option 50 and Option 75: Typically ≤--65 dBc at 2.15 GHz

attenuation

≤+9 dBmV

With 0 dB RF attenuation and preamp off. Option 50 and Option 75: When frequency is below 90 MHz: Typically <+29 dBmV (–20 dBm) When frequency is above 350 MHz: Typically ≤--21 dBmV (≤--70 dBm)

Table 1- 5: Input/Output Signal Characteristics

Characteristic Performance Requirement Supplemental Information

RF Input Type F male connector or

type N female connector

VSWR with RF Attenuation ≥10 dB 1.5:1 maximum Checked to 1 GHz

VSWR with 0 dB RF Attenuation All except Option 50 and Option 75:

2:1maximumupto1GHz

3.5:1 maximum up to 1.8 GHz Option 50 and Option 75: 4:1maximumupto2.15GHz

Maximum Safe Input +70 dBmV (0.1 W or 2.2 V) continuous

peak

100 VDC blocking capacitor

Caution: Do not apply more than 100 VDC or 100V peak AC to the RF Input

1 dB Compression Point (minimum) +34 dBmV (--15 dBm) With no RF Attenuation and 1stmixer at

+19 dBmV (--30 dBm )

2715 Spectrum Analyzer Service Manual

1- 17

Specifications

Table 1- 5: Input/Output Signal Characteristics (Cont.)

Characteristic Supplemental InformationPerformance Requirement

Ext Trig (J102) BNC connector, 10 kΩ, DC coupled for

external trigger signals

Voltage Range

Minimum Typically at least 100 mV

1MHz

Maximum 50 V (DC + peak AC)

Pulse Width 0.1 s minimum

Accessory Connector (J103) DB-15 female connector

Pin 1: External Video Input Typically 100 ohm, DC coupled, 0 -

50 kHz, 0 -- 1.6 V (200 mV/div) signal input for vertical deflection of the CRT beam. The signal is processed through the video filters and the 1 dB, 5 dB, and 10 dB scale factor circuits on the Log board. Display storage may be bypassed.

Pin 2: Sweep Gate

+2.0 V minimum (high)

0.8 V maximum (low)

TTL-compatible signal that goes to a logic high level while the CRT beam is sweeping.

Pin 3: Chassis and Signal Ground

Pin 4: Sweep Output

+1.3 V

-- 1 . 3 V

Provides a nominal +1.3 V to --1.3 V negative-going ramp, proportional to the horizontal sweep (output impedance ≤50 Ω).

Pin 5: Log Video Output Provides 0 V to +1.6 V of video signal,

inversely proportional to the vertical display amplitude. 0 V is the top of the screen. Impedance is 1 kΩ.

Pin 6: CLK0 Output Clock output to Option 05 (External

Tracking Generator). CMOS logic levels typically +3.5 V high, +1.5 V low.

Pin 7: Data I Input Data input from Option 05 (External

Tracking Generator). Typically +5 V high, +0.1 V low.

Pin 8: Data O Output Data output to Option 05 (External

Tracking Generator). CMOS logic levels, typically +3.5 V high, +1.5 V low.

Pin 9: ~EXTGLATCH Logic output to Option 05 (External

Tracking Generator). CMOS logic levels, typically +3.5 V high, +1.5 V low.

Pin 10: 26.38 MHz Input Input from Option 05 (External Tracking

Generator); typically a 0.5 V centered at +3.7 VDC.

,15Hzto

peak

p-p

sine wave

1- 18

2715 Spectrum Analyzer Service Manual

Specifications

Table 1- 5: Input/Output Signal Characteristics (Cont.)

Characteristic Supplemental InformationPerformance Requirement

Pin 11: VLVL Output DC output to Option 05 (External

Tracking Generator); typically 9.5 V with TG level set to ON.

Pin 12: SWPSLOPE Output Negative going ramp output to Option 05

(External Tracking Generator); typically 5 V with analyzer set to max span.

Pins 13 through 15 Not used

Digital Communications Port (J104) RS-232 or GPIB connector

Table 1- 6: Power Requirements

Characteristic Performance Requirement Supplemental Information

Input Voltage

Line Voltage Range 90 VAC to 250 VAC

Line Frequency Range 48 Hz to 63 Hz

Line Voltage Range 90 VAC to 132 VAC

Line Frequency Range 48 Hz to 440 Hz

Line Fuse 2ASlow-Blow

Input Power 90 W (1.2 A) for standard instrument

105 W (1.4 A) maximum with options (115 W maximum at 90 V and 440 Hz)

Leakage Current 3.5 mA

At 115 V and 60 Hz

maximum or 5 mA

RMS

maximum

peak

Table 1- 7: Supplementary Characteristics Due to Options

Characteristic Performance Requirement Supplemental Information

Option 03 Provides a GPIB interface port at J104 to

replace RS-232

Option 08 Provides a RS-232 serial interface port at

J104 to replace GPIB

Option 15 Adda1stLO output

1stLO Output Level ≥+48.8 dBmV (≥0.0 dBm) At spectrum analyzer frequencies

≥100 kHz

2715 Spectrum Analyzer Service Manual

1- 19

Specifications

Table 1- 8: General Characteristics

Characteristic Performance Requirement Supplemental Information

Sweep Normal, Single Sweep, and Manual Scan

Sweep Rate 1 s/div to 2 s/div in a 1--2--5 sequence

Accuracy ±10% over the center 8 divisions

Triggering Free Run, Internal, External, Line,

TV Line, and TV Field

Internal Trigger Level 1 division or more of signal

External Trigger Level See EXT TRIG in Table 1--5

Nonvolatile Memory (Battery-Backed Up) Instrument settings, waveforms, and

normalization results are stored in NVRAM

Battery Life (Lithium)

At +55_ C Ambient Temperature 1to2years

At +25_ C Ambient Temperature At least 5 years

Temperature Range for Retaining Data -- 1 0 _ Cto+75_ C

Internal Calibrator Provides 100 MHz marker for amplitude

calibration and comb of 100 MHz markers for frequency and span calibration

Amplitude and Accuracy +18.8 dBmV (--30 dBm), ±0.3 dB, at

100 MHz, ±2 kHz

Drift ±2 PPM/year

IF Gate Rise and Fall Times 7 s nominal

Off Isolation >60dB

1- 20

2715 Spectrum Analyzer Service Manual

Specifications

Table 1- 9: Environmental Characteristics

Characteristic Description

The Description column describes how most characteristics were derived and a description of the characteristic. This instrument meets MIL-T-28800E, Type III, Class 5, Style C Specifications.

Electromagnetic Interference (EMI)

Emissions: EN50081--1 Radiated Emissions, 30 MHz--1 GHz

EN55022 Class B (CISPR 22B)

Conducted Emissions, 150 kHz--30 MHz EN55022 Class B (CISPR 22B)

Conducted Emissions, Power Line Harmonics, 0--2 kHZ IEC 555-2/3

Immunity: EN50082--1 Electrostatic Discharge, 8 kV

IEC 801-2

Radiated Immunity, 27 MHz--500 MHz IEC 801-3 Performance Requirement: No responses above --90 dBm ina3V/meterfield

Fast Transients, Capacitive Clamp, 1 kV Power Leads, 500 V Control Leads IEC 801-4

Power Line Surge, 1 kV Differential Mode, 2kVcommonmode IEC 801-5

Temperature

Operating 0_ Cto+50_ C

Nonoperating

-- 5 5 _ Cto+75_ C

Humidity

Operating 95% RH ± 5% + 30_ C and below

75% RH ± 5% + 31_ C through + 40_ C 45% RH ± 5% + 41_ C through + 50_ C

Nonoperating Five cycles (120 hours) in accordance with MIL-STD-28800E, class 5

Altitude

Operating 15,000 ft (4.57 km)

Nonoperating 50,000 ft (15.24 km)

After storage at temperatures below - 15_ C, the instrument may not reset when power is first turned on. If this happens, allow the instrument to warm up for at least 15 minutes, then turn power off for 5 seconds an back on.

NVRAM is lost below - 10_ C.

2715 Spectrum Analyzer Service Manual

1- 21

Specifications

Table 1- 9: Environmental Characteristics (Cont.)

Characteristic Descri pti on

Vibration

Operating (Instrument secured to a vibration platform during test)

Shock (Operating and Nonoperating) Three guillotine-type shocks of 30 g, one-half sine, 11 ms duration each direction

Transit Drop (Free Fall) 8 in (203.2 mm), one per each of 5 faces and 4 corners (instrument is tested and

MIL-T-28800E, Method 514 Procedure X (modified) 15 minutes along each of 3 major axes at a total displacement of 0.015 in (0.38 mm) peak-to-peak (2.4 g at 55 Hz), with frequency varied from 10 Hz to 55 Hz in 1-minute sweeps

Hold for 10 minutes at 55 Hz

All major resonances must be above 55 Hz (resonance is defined as an excursion greater than 2X the input displacement)

along each major axis, total of 18 shocks; no drops allowed on the front surface and front corners

meets drop height of 12 in (304.8 mm)

Table 1- 10: Physical Characteristics

Characteristic Performance Requirement

Weight

With Standard Accessories 25 lbs (11.34 kg)

Without Standard Accessories 22.5 lbs (10.21 kg)

Dimensions

Height with Feet and Handle 5.4 in (137.16 mm)

Width

With Handle 14.2 in (360.68 mm)

Without Handle 12.9 in (327.66 mm)

Depth

With Front Panel Cover 17.5 in (444.50 mm)

Without Front Panel Cover 16.85 in (427.99 mm)

With Handle Extended 20.1 in (510.54 mm)

1- 22

2715 Spectrum Analyzer Service Manual

Table 1- 11: Certifications and Compliances

Category Description

Specifications

EC Declaration of Conformity -EMC

EC Declaration of Conformity -Low Voltage

Approvals UL1244 -- Standard for Electrical and Electronic Measuring and Testing Equipment

Installation Category Descriptions Terminals on this product may have different installation category designations. The installation

Meets intent of Directive 89/336/EEC for Electromagnetic Compatibility. Compliance was demonstrated to the following specifications as listed in the Official Journal of the European Communities:

EN 50081-1 Emissions:

EN 55022 Class B Radiated and Conducted Emissions EN 60555-2 AC Power Line Harmonic Emissions

EN 50082-1 Immunity:

IEC 801-2 Electrostatic Discharge Immunity IEC 801-3 RF Electromagnetic Field Immunity IEC 801-4 Electrical Fast Transient/Burst Immunity IEC 801-5 Power Line Surge Immunity

Compliance was demonstrated to the following specification as listed in the Official Journal of the European Communities:

Low Voltage Directive 73/23/EEC

EN 61010-1:1993 Safety requirements for electrical equipment for measurement,

control, and laboratory use

CAN/CSA C22.2 No. 231 – Safety Requirements for Electrical and Electronic Measuring and Testing Equipment

categories are:

CAT III Distribution-level mains (usually permanently connected). Equipment at this level is

typically in a fixed industrial location

CAT II Local-level mains (wall sockets). Equipment at this level includes appliances, portable

tools, and similar products. Equipment is usually cord-connected

CAT I Secondary (signal level) or battery operated circuits of electronic equipment

2715 Spectrum Analyzer Service Manual

1- 23

Specifications

Table 1- 12: Safety Certification Com pliance

Category Description

Temperature (operating) +5° Cto+50° C

Altitude (maximum operating) 2000 meters (6562 ft.)

Relative Humidity (maximum operating)

Equipment Type Test and Measuring

Safety Class Class I (as defined in IEC 1010-1, Annex H)—grounded product

Overvoltage Category Overvoltage Category II (as defined in IEC 1010-1, Annex J)

Pollution Degree Pollution Degree 2 (as defined in IEC 1010-1)

80% for temperatures up to 31° C, decreasing linearly to 50% at 40° C

Note: Rated for indoor use only.

Table 1- 13: Safety Standards

Operating Information

This section contains the following:

H Instrument description

H Conformance to industry standards

H Product service information

H Instrument construction

H Installation and preparation for use

H Power cord

H Fuse replacement

H Assembly and circuit numbering

H Accessories

H Menus

Instrument Description

This instrument is a compact and portable Spectrum Analyzer for the 9 kHz to

1.8GHzfrequencyrange(upto2.15GHzwithOption50orOption75 installed). Microprocessor control of most functions simplifies and enhances operation.

The Spectrum Analyzer’s main features are:

H Precision Measurements Menu selectable routines provide directions for

normalizing the internal reference (calibrator signal) to external frequency and amplitude references. After the internal reference is normalized, other menu selections provide for normalizing any instrument measurement parameter.

H Menu Operation Menu-selectable routines provide diagnostics, normaliza-

tion, adjustments, and setup of basic parameters such as center frequency, frequency span, reference level, vertical scale factor, resolution bandwidth, etc. These menus are described in Section 6: Spectrum Analyzers Menus of the 2715 Spectrum Analyzer Users Manual.

2715 Spectrum Analyzer Service Manual

2- 1

Operating Information

H Single and ∆ Markers A single marker can be enabled to show the

frequency and amplitude of a specific point on the display. Delta (∆)markers show the difference frequency and amplitude between any selected two points on the displayed waveform.

H Tracking Signal tracking holds a drifting signal to center screen.

H Center Measure When this function is activated, the instrument completes

the sweep and centers the signal nearest center screen or, with markers activated, the signal nearest the marker. A readout of center frequency and amplitude is displayed.

H Display In the Spectral mode, the numerical values of signals and setup

parameters are displayed. In the Menu mode, a menu with its selections and prompts is displayed. Any error, warning, or information messages are displayed in both modes.

Conformance to Industry Standards

Product Service

This Spectrum Analyzer conforms with the following industry safety standards and regulatory requirements.

CAN/CSA C22.2, No. 231

UL 1244 (3rd Edition) Measuring Testing Equipment

To ensure adequate product service and maintenance for our instruments, Tektronix has established Field Offices and Service Centers at strategic points throughout the United States and in countries where our products are sold. Several types of maintenance or repair agreements are available.

For example, for a fixed fee, a maintenance agreement program provides maintenance and recalibration on a regular basis. Tektronix will remind you when a product is due for recalibration and perform the service within a specified time.

Contact your local Tektronix Service Center, representative, or sales engineer for details regarding product service.

2- 2

2715 Spectrum Analyzer Service Manual

Instrument Construction

Modular construction provides ready access to the major circuits. Each circuit board containing RF sensitive circuits is mounted in a casting, with feed through connectors through the compartment walls. Most boards and assemblies plug onto a common interconnect board. Most adjustments and test points are accessible while the instrument is operational and without need of a circuit board extender.

Circuit board extenders are available in an optional Service Kit (see Maintenance section under Fixtures and Tools for Maintenance on page 6--3). Most of the modules or boards can be removed without affecting the structural or functional integrity of other modules. The extender board allows any of the six circuit board assemblies in the card cage to be positioned for service or adjustment. The Sweep and Power Supply circuit boards are accessed by removing the instrument’s cabinet (and the Variable Resolution assembly in the case of the Power Supply).

All other circuit boards are accessible by removing the instrument’s cabinet and the shielding associated with each assembly.

Operating Information

NOTE. Disassembly of some modules may require special tools and procedures. These procedures and a list of tools are located in the Maintenance section.

Most RF circuits are isolated in shielded compartments to obtain and maintain the frequency stability, sensitivity, and EMI characteristics. While shielding helps ensure a spurious free response, the closeness of the circuits reduces losses and interactions with other functions. Interconnections between compartments are made by feed through terminals rather than cables. If the compartments are opened, be sure that the shields are properly reinstalled before operating.

Installation and Preparation for Use

Refer to Section 2: Getting Started of the 2715 Spectrum Analyzer User Manual for unpacking, storage, repackaging for shipment, and installation information.

Power Cord

The power cord that is supplied with the instrument depends on the available power source (see Section 1: Specifications). Power cord options are described in Section F: Options.

2715 Spectrum Analyzer Service Manual

2- 3

Operating Information

Replacing the Fuse

Replace the line fuse with a 2 A Slow Blow fuse.

Selected Components

Some components are specifically selected to meet Tektronix specifications. These components are shown in the parts list.

Selected value components are identified in the parts list as a SEL value. The component description lists either the nominal value or a range of values.

Assembly and Circuit Numbering

Each assembly and subassembly is assigned an assembly number. Generally, each component is assigned a circuit number according to its geographic location within an assembly. The Replaceable Electrical Parts list prefixes these circuit numbers with the corresponding assembly and subassembly numbers.

Accessories

Menus

Example: R260 on assembly A14 becomes A14R260.

Example:U140 on subassembly A1 of assembly A19 is found in the electrical parts list as A19A1U140.

The Replaceable Mechanical Parts section contains part numbers, descriptions, and ordering information for all standard and optional accessories offered for this Spectrum Analyzer.

Refer to Appendix F: Accessories & Options in the 2715 Spectrum Analyzer User Manual for listings of standard and optional accessories.

Refer to Section 7: Options in this manual for information on accessories associated with options.

The Accessories at the end of the Replaceable Mechanical Parts in this manual contains information on all standard accessories currently available with this Spectrum Analyzer.

2- 4

There are eight menus of selections that are used to invoke most of the setups, operational modes, and applications.

2715 Spectrum Analyzer Service Manual

Operating Information

A menu of selections may be displayed by pressing its front panel push button. Menu push buttons are grouped together under the MENUS block. See Figure 2--1 and the Menu Structure beginning on the following page.

Figure 2- 1: 2715 Front Panel Keys

2715 Spectrum Analyzer Service Manual

2- 5

Operating Information

0 FREE RUN 1 INTERNAL 2 EXTERNAL 3LINE 4TVLINE 5 TV FIELD SWEEP MENU 6 SWEEP RATE 7 MANUAL SCAN 8 SYNC POLARITY 9 SETUP TABLE

SWP/TRG Menu Structure

HORIZONTAL LINE TRIGGERING 0 CONTINUOUS 1 KNOB SELECTABLE 2 KEYPAD ENTERED LINE 3 KEYPAD ENTRY 4 TV LINE STANDARD

2- 6

2715 Spectrum Analyzer Service Manual

UTIL Menu Structure (1 of 2)

Operating Information

1 STORED SETTINGS / DISPLAYS 2 KEYPAD ENTERED SETTINGS 3 NORMALIZATIONS 4 SYSTEM CONFIGURATION 5 INSTR DIAGNOSTICS/ADJUSTMENTS 6 SERVICE REQUEST

9MORE

0 LAST POWER-DOWN 1 FACTORY DEFAULT POWER-UP 2 USER DEFINED POWER-UP 3 User Defined 4 User Defined 5 User Defined 6 User Defined 7 User Defined 8 User Defined 9MORE*

0 FREQUENCY 1 REFERENCE LEVEL 2 SPAN/DIV 3 RF ATTENUATION 4 RESOLUTION BW 5 VIDEO FILTER 6 VERTICAL SCALE 7 SWEEP RATE

0 ALL PARAMETERS 1 FREQUENCY ONLY 2 AMPLITUDE ONLY

0 COMMUNICATION PORT CONFIG 1 SCREEN PLOT CONFIGURATION 2 PRINTER CONFIGURATION 3 INSTRUMENT CONFIGURATION 4 REAL--TIME CLOCK SETUP 5 STORED SETTINGS PROTECT 6 FILE SYSTEM DIRECTORY 7 PROTECT FILE

9 INSTALLED OPTIONS DISPLAY

Expands to registers 10--18, 20--28

and 30--39.

0 AUTO 1 FIXED

0 LOG 1 DB/DIV 1 LOG 5 DB/DIV 2 LOG 10 DB/DIV 3 LINEAR

0 GPIB

2 RS--232

0 COMM PORT 1 PLOTTER LANGUAGE 2 PLOT SPEED* 3 PLOTS PER PAGE**

5 GRATICULE LINES ON PLOT

0 AUDIO ALERT 1 MINIMUM SIGNAL SIZE 2 WAVEFORM TO PRINTER 3 WAVEFORM OUTPUT FORMAT 4 PHASELOCK 5 FREQUENCY CORRECTIONS 6 SPECTRAL DISPLAY IN MENUS 7 SWEEP HOLDOFF

0 STATUS 1 GPIB ADDRESS 2 POWER ON SRQ 3 EOI/LF MODE 4 TALK ONLY MODE

0 STATUS 1 BAUD RATE 2DATABITS 3 PARITY 4EOL 5 FLOW CONTROL 6 ECHO 7 VERBOSE

2715 Spectrum Analyzer Service Manual

0 SET DAY 1 SET MONTH 2 SET YEAR 3 SET HOUR 4 SET MINUTE 5 SET SECONDS TO :00 6 DISPLAY DATE/TIME

Displayed when selected plotter language is HPGL.

2- 7

Operating Information

1 STORED SETTINGS / DISPLAYS 2 KEYPAD ENTERED SETTINGS 3 NORMALIZATIONS 4 SYSTEM CONFIGURATION 5 INSTR DIAGNOSTICS/ADJUSTMENTS 6 SERVICE REQUEST

9MORE

0 PRINT READOUTS

9MORE

UTIL Menu Structure (2 of 2)

0 DIAGNOSTICS 1 EXTENDED DIAGNOSTICS 2 MANUAL ADJUSTMENTS 3 DEBUG MENU 4 INTERNAL PARAMETERS 5 SERVICE NORMALIZATIONS 6 DIGITAL OPTIONS DIAGNOSTICS

8 CALIBRATION MODE

Factory troubleshooting aids: not discussed in this manual.

1 DEFLECTION AMP CAL 2 DISPLAY STORAGE CAL 3 SWEEP CAL

4 CFCV1 ADJUSTMENTS 5 TOGGLE VD DAC LO/HI 6 VD DAC TO VIS CARR 7 AFC TOGGLE 8 GATE TOGGLE 9 QUERY LOCK STATUS

0 SETTINGS VERIFY 1 FILE SYSTEM MENU 2 YIG SETTLE DELAY

0 THRESHOLD 1 PROGRAMD TUNING INC 2 KNOB FUNCTION 3 MARKER TO REFERENCE LEVEL 4 MOVE MARKER TO NEXT PEAK 5 TRANSPOSE MARKERS 6 MARKER START/STOP 7 FREQUENCY START/STOP 8 TUNING INCREMENT 9 SETUP TABLE

MRK/FREQ Menu Structure

0 CENTER FREQ 1 MARKER FREQ 2 KEYPAD ENTRD INC 3 KEYPAD ENTRY 4 RETURN TO AUTO

0 FREQUENCY 1 MARKER 2 VIDEO LINE*

0 FREQ START ENTRY 1 FREQ STOP ENTRY

0 CENTER/START FREQ 1 COUNTER RESOLUTION

3 FREQ OFFSET 4 FREQ OFFSET MODE

Displayed only if KNOB SELECTABLE is se-

lected in the SWEEP MENU SETUP TABLE.

0 FREQUENCY NORMALIZATIONS 1 REFERENCE NORMALIZATIONS 2 AMPLITUDE NORMALIZATIONS

4 NORMALIZATION VALUES 5 PRINT ALL NORM VALUES 6 NORM DEBUG TO PRINTER

0 COUNTER OFF WHEN TRKG (1 HZ) 11HZ 2 1KHZ

2- 8

2715 Spectrum Analyzer Service Manual

CATV/APPL CATV Measurements Page 1 Menu Structure (1 of 3)

0 RECENTER CHANNEL xx 1 CARRIER LEVEL --- AVG POWER 2 CARRIER SURVEY 3 MODULATION DEPTH 4 AURAL (FM) DEVIATION 5 CARRIER/NOISE -- DESIRED/UNDESIRED 6 HUM/LFD 7 FREQUENCY RESPONSE 8 CATV MEASUREMENTS SETUP 9MORE

0 RUN LEVELS - POWER 1 STORE CURRENT RESULTS 2 DISPLAY RESULTS 3 PRINT CURRENT RESULTS* 4 PRINT STORED RESULTS* 5 SET UP CARRIER LEVELS 6 EXTERNAL ATTEN/AMPL

9 LEAVE CARRIER LEVEL --- AVG PWR

0 RUN CARRIER SURVEY 1 STORE CURRENT RESULTS 2 DISPLAY RESULTS 3 PRINT CURRENT RESULTS* 4 PRINT STORED RESULTS* 5 SET UP CARRIER SURVEY 6 EXTERNAL ATTEN/AMPL

9 LEAVE CARRIER SURVEY

Operating Information

TEST MODES 0 ACCURATE FREQUENCY AND AMPL 1 ACCURATE AMPLITUDE ONLY 2 FAST AMPLITUDE ONLY

0ON/OFF 1 ATTEN/AMPL ENTRY

TEST MODES 0 ACCURATE FREQUENCY AND AMPL 1 ACCURATE AMPLITUDE ONLY 2 FAST AMPLITUDE ONLY

0 RUN MODULATION DEPTH 1 STORE CURRENT RESULTS 2 DISPLAY RESULTS 3 PRINT CURRENT RESULTS* 4 PRINT STORED RESULTS* 5 SET UP ADJUSTMENT MODE 6 ENTER ADJUSTMENT MODE

9 LEAVE MODULATION DEPTH

0 RUN FM DEVIATION 1 STORE CURRENT RESULTS 2 DISPLAY RESULTS 3 PRINT CURRENT RESULTS* 4 PRINT STORED RESULTS* 5 SET UP AURAL (FM) DEVIATION 6 ENTER ADJUSTMENT MODE

9 LEAVE AURAL (FM) DEVIATION

RS-232 only.

0ON/OFF 1 ATTEN/AMPL ENTRY

0 VIEW MODULATION MODE 1 TARGET LINE 2 CYCLE DELAY 3 TARGET LINE DURATION

TEST MODES 0 INTERACTIVE 1AUTO

5 MEASUREMENT TIME

2715 Spectrum Analyzer Service Manual

2- 9

Operating Information

CATV/APPL CATV Measurements Page 1 Menu Structure (2 of 3)

0 RECENTER CHANNEL xx 1 CARRIER LEVEL -- AVG POWER 2 CARRIER SURVEY 3 MODULATION DEPTH 4 AURAL (FM) DEVIATION 5 CARRIER/NOISE -- DESIRED/UNDESIRED 6 HUM/LFD 7 FREQUENCY RESPONSE 8 CATV MEASUREMENTS SETUP 9MORE

0 RUN C/N -- D/U 1 STORE CURRENT RESULTS 2 DISPLAY RESULTS 3 PRINT CURRENT RESULTS 4 PRINT STORED RESULTS

5 SET UP CARRIER/NOISE

7 IN --SERVICE 9 LEAVE C/N --- D/U

0 RUN HUM/LFD 1 STORE CURRENT RESULTS 2 DISPLAY RESULTS 3 PRINT CURRENT RESULTS* 4 PRINT STORED RESULTS* 5 POWER LINE FREQ

9 LEAVE HUM/LFD

0 RUN FREQ RESP

CURRENT REFERENCE

5 SET UP FREQ RESP

9 LEAVE FREQUENCY RESPONSE

RS-232 only.

TEST MODES 0 INTERACTIVE 1 AUTO 2 AUTO (PAUSE FOR CARRIED OFF)

5 NOISE NORM’D BW

TEST MODES 0 ✱NO REF 1WITHREF SWEEP RANGE 2 START FREQUENCY 3 STOP FREQUENCY 4 USE DEFAULT START/STOP

TEST MODES 0NOREF 1 ✱WITH REF REFERENCE ACQUISITION 2 START FREQUENCY 3 STOP FREQUENCY 4 USE DEFAULT START/STOP 5 ACQUIRE NEW REFERENCE 6 STORED REFERENCE MENU 7 EDIT CURRENT REFERENCE NAME

2- 10

2715 Spectrum Analyzer Service Manual

CATV/APPL CATV Measurements Page 1 Menu Structure (3 of 3)

To CATV/APPL CATV Measurements Page 2

0 EXIT CATV MEASUREMENT MODE 1 CHANNEL TABLE 2 SKIP CHANNEL 3 ALL CHANNELS 4SITE 5 OPERATOR 6 REF LEVEL UNIT 7 EDIT CHANNEL TABLE 8 REMOVE ALL STORED RESULTS 9 LEAVE CATV MEASUREMENTS SETUP

Operating Information

0STD 1 HRC 2IRC 3 User Defined 4 User Defined 5 User Defined 6 User Defined 7 User Defined 8 User Defined 9 User Defined

Option 50 and Option 75 only

2715 Spectrum Analyzer Service Manual

2- 11

Operating Information

CATV/APPL CATVMeasurements Page 2 Menu Structure (1 of 2)

0 ADJACENT CHANNEL LEAKAGE 1 VIEW MODULATION (FIELD) 2 VIEW MODULATION (LINE) 3 VIEW PICTURE 4LISTEN 5 CTB 6CSO 7 CROSS MODULATION 8 IN-CHANNEL RESPONSE 9MORE

0 RUN CTB 1 STORE CURRENT RESULTS 2 DISPLAY RESULTS 3 PRINT CURRENT LEVELS* 4 PRINT STORED RESULTS* 5 SET UP CTB 6 DIGITAL/ANALOG

9 LEAVE CTB

0 RUN CSO 1 STORE CURRENT RESULTS 2 DISPLAY RESULTS 3 PRINT CURRENT LEVELS* 4 PRINT STORED RESULTS*

5 SET UP CSO 6 DIGITAL/ANALOG 7 IN-SERVICE 9 LEAVE CSO

RS-232 only.

0 RUN ADJACENT CHANNEL LEAKAGE 1 STORE CURRENT RESULTS 2 DISPLAY RESULTS 3 PRINT CURRENT RESULTS* 4 PRINT STORED RESULTS* 5 MEASURE SIDE

9 LEAVE ACL

TEST MODES 0 INTERACTIVE 1 AUTO 2 AUTO (PAUSE FOR CARRIER OFF) 3 SINGLE-SWEEP

5 SET UP TEST FREQUENCIES**

TEST MODES 0 INTERACTIVE 1 AUTO 2 AUTO (PAUSE FOR CARRIER OFF) 3 SINGLE-SWEEP 4 CONTINUOUS 5 SET UP TEST FREQUENCIES AND

CONTINUOUS MODE PRMTRS**

TEST FREQUENCIES 0 User Defined 1 User Defined 2 User Defined (+0.00000HZ Default) 3 User Defined 4 User Defined 5 USE DEFAULT TEST FREQUENCIES

2- 12

TEST MODES IN-SERVICE 0 INTERACTIVE 1AUTO

5 SET UP TEST FREQUENCIES**

Not displayed in INTERACTIVE mode.

2715 Spectrum Analyzer Service Manual

TEST FREQUENCIES 0 User Defined (+1.25000MHZ Default) 1 User Defined (+750.000KHZ Default) 2 User Defined 3 User Defined (-750.000KHZ Default) 4 User Defined (-1.25000MHZ Default) 5 USE DEFAULT TEST FREQUENCIES CONTINUOUS MODE PARAMETERS*** 6 CARRIER FREQ*** 7 TEST INTERVAL*** 8 NORMALIZATION INTERVAL***

***

Displayed only if CONTINUOUS mode

is selected.

0 ADJACENT CHANNEL LEAKAGE 1 VIEW MODULATION (FIELD) 2 VIEW MODULATION (LINE) 3 VIEW PICTURE 4LISTEN 5 CTB 6CSO 7 CROSS MODULATION 8 IN-CHANNEL RESPONSE 9MORE

To CATV/APPL CATV Measurements Page 1

Operating Information

CATV/APPL CATV Measurements Page 2 Menu Structure (2 of 2)

0 RUN CROSS MODULATION 1 STORE CURRENT RESULTS 2 DISPLAY RESULTS 3 PRINT CURRENT RESULTS* 4 PRINT STORED RESULTS*

9 LEAVE CROSS MODULATION

0 RUN IN-CHAN RESP 1 STORE CURRENT RESULTS 2 DISPLAY RESULTS 3 PRINT CURRENT RESULTS* 4 PRINT STORED RESULTS* 5 SET UP IN-CHAN RESP 6 TEST SIGNAL LINE NUMBER** 7 IN-SERVICE 9 LEAVE IN-CHAN RESP

RS-232 only.

Displayed only when IN-SERVICE is On.

TEST MODES 0 INTERACTIVE 1 AUTO (PAUSE FOR SIGNAL ON) TEST FREQUENCIES 2 User Defined (-500.000KHZ Default) 3 User Defined (+500.000KHZ Default) 4 User Defined (+1.25000MHZ Default) 5 User Defined (+2.00000MHZ Default) 6 User Defined (+3.00000MHZ Default) 7 User Defined (+3.75000MHZ Default) 8 USE DEFAULT TEST FREQUENCIES

2715 Spectrum Analyzer Service Manual

TEST MODES IN-SERVICE 0 INTERACTIVE 1 AUTO TEST FREQUENCIES 2 User Defined (-500.000KHZ Default) 3 User Defined (+500.000KHZ Default) 4 User Defined (+1.25000MHZ Default) 5 User Defined (+2.00000MHZ Default) 6 User Defined (+3.00000MHZ Default) 7 User Defined (+3.75000MHZ Default) 8 USE DEFAULT TEST FREQUENCIES

2- 13

Operating Information

0 BANDWIDTH MODE 1 CARRIER TO NOISE 2 NOISE NORM’D 3 SIGNAL SEARCH MENU 4 OCCUPIED BW

7 FM DEVIATION MODE 8 CATV MEASUREMENT MODE 9 SETUP TABLE

CATV/APPL Applications Menu Structure

0 BEGIN FREQ 1 END FREQ 2 START TEST 3 DISPLAY RESULTS

0 DB DOWN FOR BW MODE 1 NORM BW FOR C/N 2 NOISE NORM’DBW 3 PERCENT OCCUPIED BW

DEMOD Menu Structure

0OFF 1 AM DEMODULATOR 2 FM DEMODULATOR 3 BROADCAST (AM) VIDEO

9 VIDEO MONITOR SETUP 0 VIDEO DETECT MODE

1 SYNC POLARITY 2 VIDEO POLARITY

2- 14

2715 Spectrum Analyzer Service Manual

0 DIGITAL/ANALOG 1 ENSEMBLE AVERAGING 2 B, C MINUS A 3 B, C MINUS A OFFSET TO 4 ACQUISITION MODE 5TITLEMODE 6 GRATICULE ILLUMINATION 7 DISPLAY SOURCE (AM) 8 DISPLAY LINE 9MINHOLD

Operating Information

DSPL Menu Structure

1 INITIATE AVERAGING 2 TERMINATE AVERAGING 3MAX 4 MEAN 5MIN 6 MAX/MIN 7 NUMBER OF AVERAGES 8 SAVE RESULTS IN DISPLAY

1TITLEMODE 2 TITLE MODE EDIT 3 PLOT LABELING 4 PLOT LABELING EDIT

0 User Defined 1 User Defined 2 User Defined 3 User Defined 4 User Defined 5 User Defined 6 User Defined 7 User Defined 8 User Defined 9 USER DEF PROGRAM UTILITIES

1ON/OFF 2 VALUE ENTRY 3 DISPLAY LINE TO MARKER 4 LIMIT DETECTOR

USERDEFMenuStructure

0 ACQUIRE KEY STROKES 1 TITLE EDIT 2 WAIT FOR END OF SWEEP 3 DISPLAY MESSAGE 4 PAUSE FOR “USER DEF” KEY 5 CONTINUOUS EXECUTION 6 STORE 7 DELETE 8 PROTECT 9 TIME DELAY SETUP

0 SET DAY 1 SET HOUR 2 SET MINUTE 3 REPEAT INTERVAL 4 RUN N TIMES 5 CLEAR TIME

2715 Spectrum Analyzer Service Manual

2- 15

Operating Information

1 PREAMP

INPUTMenuStructure

3 REF LEVEL UNIT 4 1ST MXR INPUT LVL 5 RF ATTENUATION 6 EXTERNAL ATTEN/AMPL

9 CAL SIG @ 100MHZ 18.8DBMV

0DBM 1 DBMV 2DBV 3 DBUV 4 DBUW 5 DBUV/M IN WFM x

9 DBUV/M SETUP

0ON/OFF 1 ATTEN/AMPL ENTRY

0 EDIT ANTENNA TABLE 1 User Defined 2 User Defined 3 User Defined 4 User Defined 5 User Defined 6 MEASUREMENT DIST 7 SAVERESULTSINWFM

9 MARKER DISPLAY

0 BEGIN EDIT 1 TITLE EDIT 2STORE 3LOAD 4 DELETE 5 PRINT 6 ANTENNA SETUP

1 START FREQUENCY 2 STOP FREQUENCY 3 INC FREQUENCY 4 REFERENCE DISTANCE

2- 16

2715 Spectrum Analyzer Service Manual

Theory of Operation

This section describes the 2715 circuitry. The section begins with a functional description of the major circuit blocks. This is followed by more detailed descriptions of the circuitry within each block. While reading these descriptions, refer to the corresponding diagrams in Section 9: Diagrams.

Block Diagram Description

The Spectrum Analyzer block diagram contains the following major blocks:

H Attenuator and Low Pass Filter

H 1st Converter

H 2nd Converter

H RF Mother Board (3rd Converter)

H VR (Variable Resolution Module)

H Log Amplifier

H Display Storage board

H Center Frequency Control

H 1st LO Buffer

H Microprocessor

H Sweep

H Power Supply (Deflection)

This is a block diagram description of the Spectrum Analyzer. While reading this description, refer to Figure 3--1.

NOTE. The power levels noted in the block diagram between the input and the Log Amplifier assume a --30 dBm (+18.8 dBmV) input level.

The block diagram shows how the major sections in the instrument relate. It also shows the paths of most major signals. Not explicitly shown are the interconnections between the Power Supply and the circuit blocks, interconnections between the Sweep board and other major circuit blocks, and interconnections between the Deflection System and other circuit blocks. (The Deflection System is located on the Power Supply board.)

2715 Spectrum Analyzer Service Manual

3- 1

Theory of Operation

A25Ω resistor within the RF INPUT connector assembly is placed in series with the signal path. This transforms the connector to a 75 Ω impedance for external signal connections. All RF signal connections within the 2715 (SMA and SMB connectors) have a 50 Ω impedance. RF type signal connections between modules are made using double shielded coaxial cables, while DC type signal connections are made using either multipin jacks on the Power Supply board (Power Supply, Log Amplifier, Display Storage, Microprocessor, and Center Frequency Control boards) or small ribbon cables.

The Main Interconnect Diagram at the front of the Diagrams section provides a chart of the interconnect system in addition to what is shown in Figure 3--1. Block diagrams showing more detail of these main sections appear before the appropriate schematics together with another description. Circuit schematic diagrams follow the Main Interconnect Diagram.

RF IN

9kHz-1.8GHz

+70 dBmV MAX,

75 Ω 100 VDC

Max

Calibrator

(100 MHz/

-- 22 dBm)

Attenuator

Reference

Oscillator

1st LO

Center

Frequency

Control

2110 MHz

1st

Converter

2.11 − 3.91 GHz +11 dBm MIN +14.5 dBm MAX

From 1st LO Buffer

SWPSLOPE

10/

2nd LO

RF Mother Board

2nd

Converter

2GHz100 GHz

110 MHz

Power Supply

with Deflection

System

Front Panel

Rear Panel

Controls & Connector

COUNT10/

3rd

Converter

10 MHz

Log

Amplifier

Variable

Resolution

Module

10 MHz

-- 10 dBm

Log

Amplifier

Micro-

processor

Options

Display

Storage

50/

Digital

Port

9 KHz – 2.15 GHz for Option 50 and Option 75

2.11 – 4.26 GHz for Option 50 and Option 75

Figure 3- 1: Main Block Diagram

3- 2

2715 Spectrum Analyzer Service Manual

Theory of Operation

What It Does

How It Works

Attenuator and Low Pass

Filter

The Spectrum Analyzer accepts an electrical signal as its input and displays the signal’s frequency components on a CRT. Signals are applied directly to the RF INPUT.

The display of the input signal appears on the CRT as a graph where the horizontal axis is frequency and the vertical axis is amplitude.

The Spectrum Analyzer operates as a variable bandwidth receiver. The CRT beam moves horizontally as a range of frequencies is scanned. When a frequency component of an input signal is detected, the beam is deflected vertically as a function of input power at that frequency.

There are two selections for inputs to the Spectrum Analyzer: the RF INPUT at the front panel and the internal calibrator signal.

The Attenuator adds attenuation to the input signal such that the level at the input of the 1st mixer (1st Converter) is limited to no more than --30 dBm. This would represent a full screen signal. Also, an amplifier can be inserted in the signal path to improve sensitivity when small signals are applied to the RF INPUT by invoking the Preamp mode. The Microprocessor sets the amount of attenuation, depending on the user selected reference level, to maintain the proper signal level.

Converter and

Bandpass Filter

Converter

The signal is then routed to the 1st Converter through a Low Pass Filter. The Low Pass Filter attenuates out-of-band signals and helps minimize 1st Local Oscillator (LO) emission at the RF INPUT. When the Preamp mode is invoked, the Microprocessor sets the appropriate amount of attenuation, or it sets the gain of an internal amplifier (Variable Resolution) to maintain a calibrated display.

The input signal is converted to an intermediate frequency (IF) signal of 2110 MHz. This is accomplished by mixing the input signal with an LO signal that varies over a range of 2.11 GHz to 3.91 GHz (4.26 GHz for Option 50 and Option 75). The LO range corresponds to a range of 0 Hz to 1.8 GHz (2.15 GHz for Option 50 and Option 75) at the RF INPUT. The output of the mixer is then amplified to compensate for the conversion loss, and it is filtered to allow only the difference frequency to pass. All other mixer products are attenuated.

The 2nd Converter down converts the 2110 MHz IF signal to 110 MHz, then routes this 2nd IF to the RF Mother board.

2715 Spectrum Analyzer Service Manual

3- 3

Theory of Operation

RF Mother Board

Assembly

Variable Resolution

Module

Log Amplifier

The RF Mother board assembly contains a 2 GHz 2nd LO, a 2nd Converter, several gain stages, a 5 MHz resolution bandwidth filter, and a 3rd Converter. The 2nd Converter down converts the 2110 MHz 1st IF to 110 MHz. The 3rd Converter down converts the 110 MHz 2nd IF to a 10 MHz 3rd IF. This signal is routed to the Variable Resolution module.

The Variable Resolution contains several selectable gain stages prior to the filters and a compensation amplifier. One of the nine filters is selected. Each filter has an attenuator pad associated with it to compensate for losses in the filter. The system selects the appropriate amplification factor as each filter is selected.

The 10 MHz IF signal is processed through one of several Bandpass filters, amplified once more, and then routed to the Log Amplifier board.

The Log Amplifier performs the logarithmic conversion, linear detection and logarithmic detection of the incoming signal, and amplitude calibration. The log display has scale factors of 10 dB/div, 5 dB/div, and 1 dB/div. The module also contains an FM detector, an audio amplifier, an amplitude limited output for the period counter, and an out-of-band signal clamp.

The detector produces a voltage that corresponds to the input signal strength in decibels. The detector output is then vertically scaled and sent to the Display Storage and Sweep boards.

Display Storage

The control processor uses three 8 bit shift registers to control the Log Amplifier.

The Display Storage board contains the circuitry for putting text and waveforms onto the CRT display.

This board contains the following programmable functions:

H Waveform Storage — four 512 point waveforms

H Dot Markers — up to two intensified markers

H Text Storage — four 32 character by 16 lines of text

H Accumulator data — direct access to the output of the A to D converter

H Nonvolatile memory — 32 Kbytes total; 2 Kbytes used for waveforms;

2 Kbytes used for text; the rest is available for general use

When enabling the analog display, waveforms A, B, C, and D are turned on, but not displayed. This results in a chopped blanking effect between the readout and the analog display. The scanning alternates between the readout and the analog display.

3- 4

2715 Spectrum Analyzer Service Manual

The Display Storage board is capable of storing four waveforms of 512 bytes each, four pages of text of 512 bytes each, and up to two markers. Any combination of waveforms and text may be displayed on the CRT. If any waveforms are being displayed, the text portion of the display is limited to approximately 100 characters in order to avoid flicker.

Only one page of text may be displayed at any one time. The readout page is limited to approximately 100 characters.

The waveforms and text displays are accessed through memory reads and writes. When (DISPLAY) A, B, C, or D is selected, the stored waveforms in those registers are displayed. When A, B, C, and D are deselected, the display reverts to the real time (nondigitized) video waveform, and the readout is updated during the readout cycle.

Center Frequency Control

The Center Frequency Control system provides 1st Local Oscillator (1st LO) signal to the 1st Converter at the center frequency and span selected by the user. In general, this is accomplished by a combination of setting, counting, and resetting (as required) of the frequencies of various oscillators.

Theory of Operation

1stLO

The system is expected to control the frequency within a few Hz out of a total operating range of approximately 2 GHz.

The principal elements of the frequency control system are as follows:

This is a YIG tuned oscillator that covers the range of 2.11 to 3.91 GHz or 2.11 to 4.26 GHz for Option 50 and Option 75 (YIG = Yttrium Iron Garnet.) Ideally, its operating frequency is exactly proportional to the strength of an internal DC magnetic field. This field is the combined field of two coils, one large (Main) and one small (FM). In practice, the frequency is uncertain by up to a few MHz due to problems such as temperature drift, slight nonlinearity, and magnetic hysteresis. Also, the oscillator has some residual FM and phase noise sidebands due to internal causes and external noise and drift from the driver circuit. The remainder of the frequency control system maintains the oscillator (abbreviated YIG) at the right frequency. Usually, it is sufficient to set the YIG, then periodically check its frequency and make small adjustments as required. However, in very narrow spans the YIG must be phase locked to a stable source in order to maintain sufficient stability.

The 1st LO Interface provides drive signals for the main coil and FM coil, a control signal for the main coil, and power for the gain stage.

2715 Spectrum Analyzer Service Manual

3- 5

Theory of Operation

100 MHz Reference

Oscillator

Phase Gate

This is a precision, temperature controlled, quartz crystal oscillator that provides the reference around which all instrument frequency related performance revolves. It is designed for maximal frequency stability over temperature and time, with absolute frequency accuracy being secondary. The instrument firmware accounts for any frequency inaccuracy, producing a virtually perfect reference.

The phase gate is a high speed sampling switch that takes a very brief sample of the 1st LO waveform once during each cycle of the strobe frequency. (The strobe is a control signal supplied to the phase gate from an external source.) These samples are later averaged by a low pass filter to eliminate ripple at the strobe frequency, and also to eliminate other undesirable components.

When the 1st LO is phase locked to any integer multiple of the strobe frequency, the resulting output is a phase dependent DC voltage that is used as the error voltage in a feedback loop to maintain phase lock.

When the 1st LO is not phase locked, the resulting output is a beat note occurring at the difference frequency between the 1st LO frequency and the nearest integer multiple of the strobe frequency. (Actually, many beat frequencies are present at once, but the low pass filter eliminates all but the one of lowest frequency.)

Phase Lock Center

Frequency Control

(PLCFC)

Firmware

This element is the focal point of the frequency control system hardware. It accepts commands from the instrument microprocessor and then puts out appropriate drive signals to the 1st LO as well as a suitable strobe signal to the Phase Gate. The PLCFC module also uses the Phase Gate output. It also provides counter signals and status information to the microprocessor. It requires the 100 MHz reference signal in order to function.

Because of the variety of tasks that the Spectrum Analyzer is called upon to do, it is essential to have an intelligent controller. This is especially true in the frequency control context, because the required degree of control could not be economically obtained with unassisted analog hardware.

Instrument firmware has the task (among many others) of commanding the frequency control hardware, taking feedback from it, and making readjustments as required to obtain the desired result.

The interface between the microprocessor system and the PLCFC module is through a pair of serial data lines, some latch lines, and some clock signals.

3- 6

2715 Spectrum Analyzer Service Manual

1stLO Buffer

Sweep

Theory of Operation

The 1st LO Buffer consists of a Leveled Amplifier and a Phase Gate Detector. The Leveled Amplifier provides the LO input drive for the 1st Mixer. The Phase Gate Detector logs 1st LO drift. That information is then used for frequency corrections.

The Sweep board contains a microprocessor interface, horizontal sweep generator, trigger circuitry, vertical sweep (raster scan) circuitry, video processing, video line triggering, and graticule illumination.

This board receives messages from the microprocessor regarding its operation, but cannot send messages directly to the microprocessor.

Various combinations of resistors and capacitors yield the sweep speed selections.

The available trigger modes are Free Run, Internal, Line, External, TV Field, and TV Line. When the video monitor mode is selected, the readout, display storage, and video filter are turned off. In addition, the resolution bandwidth is set to 5 MHz, the Vertical display mode defaults to Lin, the span setting defaults to Zero Span, and the sweep rate defaults to 5 s. The video monitor mode is turned off from the trigger menu or by selecting another trigger mode.

TV Line Trigger mode causes the Spectrum Analyzer to trigger on the selected video line. The selected line, and part of the next line, are displayed.

2715 Spectrum Analyzer Service Manual

3- 7

Theory of Operation

Display System

The Display System consists of the Vertical Display circuit, Horizontal Display circuit, and Z Axis circuit. See Figure 3--2.

The Display System has three possible display modes. The active spectrum display mode displays the incoming signal. The static spectrum display mode displays stored signals from memory. The video monitor mode displays live video signals.

Part of Power Supply Board

Log

Amplifier

Display

Storage

Sweep

Front

Panel

LOGVIDEO

DSVER

DSHOR

SWP

VIDVERT

VIDZ

CRTINTS

To Ver tic al Deflection Plates

To Horizontal Deflection Plates

To Z Ax is

3- 8

Figure 3- 2: Display System Diagram

2715 Spectrum Analyzer Service Manual

Circuit Description

The following sections provide detailed circuit descriptions and is arranged to follow the input signal flow. While reading these descriptions, refer to the corresponding diagrams in Section 9: Diagrams.

Attenuator and 1stConverter

The Attenuator and 1st Converter signal path consists of the following parts:

H Step Attenuator

H 1.8 GHz Low Pass Filter (2.2 GHz Low Pass Filter for Option 50 and Option

75)

H Mixer

Theory of Operation

Step Attenuator

H 4.5 GHz Low Pass Filter

H 2110 MHz Bandpass Filter

The Spectrum Analyzer input frequency range is 9 kHz to 1.8 GHz (2.15 GHz for Option 50 and Option 75). The low end of the frequency range is determined by a capacitor on the Attenuator board, the narrowest resolution filter in the Variable Resolution assembly, and FM characteristics of the 1st LO (YIG Oscillator).

The signal comes in at the front panel RF INPUT connector. The 75 Ω RF INPUT connector is connected to a 0 to 50 dB step attenuator, capable of stepping from 0 to 50 dB in 2 dB steps. The Attenuator consists of relay controlled pads of 2, 4, 8, 16, and 20 dB. The instrument firmware controls the relays to provide the necessary attenuation to maintain a calibrated reference level.

2715 Spectrum Analyzer Service Manual

3- 9

Theory of Operation

A relay switch at the input of the Step Attenuator selects the RF input signal or the internal calibrator signal. See Figure 3--3. Since the calibrator signal comes into the Step Attenuator assembly ahead of the attenuators, it can be used to verify the accuracy of the Step Attenuator and other parameters. Selection is made through the INPUT MENU.

RF IN

75 Ω

Calibrator

100 MHz/−22 dBm

2.2 GHz for Option 50 and Option 75

2.11 – 4.26 GHz for Option 50 and Option 75

Step Attenuator

Attenuator

Figure 3- 3: Attenuator and 1st Converter Diagram

Also, an amplifier with 18 to 20 dB of gain may be inserted in the signal path at the output of the Step Attenuator. This is the Preamp mode, selectable through the INPUT MENU. It is used to enhance sensitivity, when small signals are applied to the input, by maintaining the same signal to noise ratio from the input to the 2nd Converter. When a small signal is applied to the RF INPUT, and the Preamp mode is activated, both the signal and the noise level are amplified an equal amount. Any attenuation less than the gain of the preamp will then attenuate both the signal and the noise. Thus, signal to noise ratio remains nearly constant. In the meantime, the instrument makes corrections in the IF to maintain a calibrated reference level.

PREAMP

1.8 GHz

1st Converter

2.11–3.91GHz

From 1st LO Buffer

2110 MHz4.5 GHz

2110 MHz to 2nd Converter

3- 10

Low Pass Filter

The Low Pass Filter attenuates all out-of-band frequencies. It rejects all frequencies above 1.8 GHz (above 2.2 GHz for Option 50 and Option 75), preventing them from reaching the mixer input and creating unwanted images. It also reduces emissions from internally generated frequencies above 1.8 GHz (above 2.2 GHz for Option 50 and Option 75).

2715 Spectrum Analyzer Service Manual

Theory of Operation

1stConverter

Bandpass Filter

The 1st Converter converts the incoming RF signals to the 1st IF. Input signals are applied through the Step Attenuator and Low Pass Filter and through the 1st LO Buffer Amplifier.

The 1st Converter receives the RF signal through the Low Pass Filter and a 1st LO signal from the 1st LO Buffer Amplifier. These signals combine to produce mixing products that are filtered to yield the 2110 MHz IF signal.

The mixer output is coupled to the input of a balanced amplifier where the signal is split into two paths. The signals in the two paths are 90 degrees out of phase. The signals are recombined at the output, yielding a gain of approximately 10 dB. Any reflections to the input are dissipated in a 50 Ω termination. The output is also terminated in 50 Ω to assure a match at the output port.

The Bandpass Filter (a four cavity filter) is a low loss, narrow band filter that only passes the 2110 MHz IF signal to the 2nd Converter. Any other frequencies are reflected back to the 1st Converter and dissipated in the termination. In addition, the filter prevents the 2nd Converter LO and mixer products from feeding back into the 1st Converter.

Each end resonator is capacitively coupled to external circuits through a coupling hat plugged into a 3 mm connector. Inter cavity coupling is provided by coupling loops that protrude from the machined filter top. The resonant frequency of each cavity is determined primarily by the depth of a gap in the underside of the filter top and is fine tuned with a tuning screw on the side of each cavity. When properly tuned, the filter return loss is >25 dB from either end (in a 50 Ω system). Figure 3--4 shows the equivalent electrical circuit.

RF Input

Figure 3- 4: Equivalent Circuit for the Bandpass (4 Cavity) Filter

2715 Spectrum Analyzer Service Manual

Cavity 1

Coupling Loops

Cavity 2 Cavity 3 Cavity 4

Cavity L and C

Tuning Screw

3- 11

Theory of Operation

RF Mother Board and Phase Locked 2nd LO

This section contains a detailed description of the RF Mother board and Phase Locked 2nd Local Oscillator.

Overview

RF Mother Board

Block Diagram

The RF Mother board converts the 1st IF frequency to 10 MHz in two frequency conversions. The first conversion (2nd mixer) mixes the 2.11 GHz 1st IF with the 2 GHz 2nd LO to create a 110 MHz second IF. The 2 GHz LO is generated on the board and is phase locked to the 100 MHz crystal reference. The 110 MHz 2nd IF is amplified (with variable gain) and filtered by a 5 MHz bandpass filter. A portion of the 2nd IF signal is sent to the sweep board for use by the satellite demodulator. The 3rd conversion mixes the 2nd IF with the 100 MHz reference to produce the 3rd IF frequency of 10 MHz. This signal is amplified and sent to the variable resolution module.

This section provides a block diagram description of the RF Mother board as illustrated in Figure 3--5.

2110 MHz IF

100 MHz

110 MH z Sample

BPF

3- 12

10 MHz IF

Figure 3- 5: Block Diagram of RF Mother Board

The RF Mother board converts the 1st IF frequency (2.11 GHz) down to 110 MHz by mixing it with a 2 GHz LO. This LO is created by phase locking a VCO to the 100MHz reference frequency. This reference is provided by the Reference Oscillator module.

2715 Spectrum Analyzer Service Manual

Theory of Operation

The 110 MHz 2nd IF is amplified and divided along two paths. One path is through a buffer amplifier to the sweep board where the signal is available to the satellite demodulator. The second path is through a PIN attenuator which sets the gain of the module. The signal then passes through a second amplifier stage then a 110 MHz Bandpass filter. This filter has a 3 dB bandwidth of 5 MHz which sets the widest resolution bandwidth of the instrument. After the 5 MHz filter, the signal is again amplified and applied to the 3rd converter.

The 3rd IF is created by mixing the 2nd IF with the 100 MHz reference to create the 3rd IF frequency of 10 MHz. The mixer output is filtered to reduce the 2nd harmonic level, and then amplified before being applied to the VR module.

Detailed Circuit

Descriptions

This section describes specific elements of the RF Mother board.

2 GHz Phase locked LO. The 2nd local oscillator is formed by Q112 and C204. In this configuration, the VCO oscillates into a 50 Ω load. The resonator ensures that this frequency will be close to 2 GHz. The VCO is tuned by varying the emitter base voltage, which causes that junction to act as a varactor.

A sample of the 2 GHz signal is divided by 4 (U424) and sent to a mixer/phase detector (U511). The mixer is driven by the 100 MHz reference, so the DC mixer output is created by the divide-by-4 sample and the 5th harmonic of the 100 MHz reference. This signal is integrated (U444) and connected to the Q112 emitter, closing the loop.

U230A provides a clean --8 V bias to Q223. If the loop is unlocked U230B causes the control loop to oscillate, sweeping over its full range until lock occurs. C323 (10F) and related circuitry insures start up by pulling the control voltage high at turn on.

2nd Mixer. This single balanced mixer is formed by CR223. The 2 GHz 2nd LO is applied to the diodes through amplifier (Q322), and the 2.11 GHz input and 110 MHz 2nd IF are separated by a filter.

110 MHz Amplifiers. These IF amplifiers consist of common emitter transistors (Q130, Q140, and Q150) with both series and parallel feedback. The 1:1 transformers (T130, T140, and T150) provide lower output impedance for better intermodulation distortion performance.

PIN Attenuator. CR369 and CR367 are PIN diodes and are used to adjust the gain of the module. PIN diodes behave like resistors at RF frequencies, with the value being dependent on current flowing in the diode. (High current, low resistance; low current, high resistance). Current through CR369 decreases attenuation and current through CR367 increases attenuation. R200 adjusts the current through the PIN diodes and has a range of approximately 15dB attenuation.

2715 Spectrum Analyzer Service Manual

3- 13

Theory of Operation

110 MHz Bandpass Filter. This filter is a 5th order, shunt resonator Butterworth filter.

3rd Mixer. U665 and its associated circuitry make up the 3rd mixer.

Output Amplifier. This IF amplifier consists of a common emitter transistor

(Q670) with both series and parallel feedback. The 1:1 transformer (T670) provides lower output impedance for better intermodulation distortion performance. The resistive attenuator at the output is used to match the load to the variable resolution. It also provides some high frequency roll off.

1stLO Interface, 1stLO, and 1stLO Buffer Amplifier

This section contains a detailed description of the 1st LO Interface, 1st LO and 1st Buffer Amplifier.

1stLO Interface

and 1

The 1st LO has a tuning range of 2.11 to 3.91 GHz (2.11 to 4.26 GHz for Option 50 and 75). The oscillator assembly includes the interface circuit board that couples operating and tuning voltages from the Center Frequency Control board.

Two Zener diodes on the Interface board clamp transient voltages from the main coil. See Figure 3--6.

1st LO1st LO Interface

+Main

SWP Main

−Main

+FM

1st LO Out to 1st LO

−FM YIG Sphere

Buffer Amplifier

3- 14

−V

Figure 3- 6: 1st LO Interface and 1st LO Diagram

2715 Spectrum Analyzer Service Manual

Theory of Operation

When the FM coil is used to sweep the oscillator, the relay on the Interface board closes and couples a large capacitor (two capacitors in parallel) across the main coil. The capacitors lower the noise bandwidth of the main coil driving circuit while the FM coil is in operation. The heater provides temperature stability. The rest of the circuitry on the Interface board provides operating voltages for the two amplifiers in the 1st LO assembly.

The output of the 1st LO drives the 1st LO Buffer Amplifier.

1stLO Buffer Amplifier

1st LO In

The 1st LO Buffer Amplifier consists of the following:

H Automatic Level Controlled (ALC) Amplifier

H Strobe Driver

H Sampling Gate

ALC Amplifier. The A LC Amplifier is composed of a wide band amplifier with impedance matching transmission lines at the input and output, a directional coupler, a detector, a level comparator, and active bias. See Figure 3--7.

Detector

-- V R E F

1st LO Out

ALC Amplifier

Terminator

replaced by semi-rigid cable when Option 15

is installed

Reserved for Options

STROBE from Center

Frequency Control Board

(25.7325 MHz to 26.05 MHz)

Figure 3- 7: 1st LO Buffer Amplifier Diagram

2715 Spectrum Analyzer Service Manual

Strobe Driver

Beat Note to Phase

Lock CFC Module

Sampling

Gate

3- 15

Theory of Operation

The directional coupler couples approximately --15 dBm of the amplified LO signal to the detector. The coupled signal is then amplitude detected, and the resultant DC level fed to the noninverting input of a comparator, where it is compared to a reference DC level. (The reference DC level is connected to the inverting input.) The output of the comparator then controls the active bias tending to hold the amplifier’s output at a constant level.

Strobe Driver. A Strobe signal from the Center Frequency Control assembly is coupled to the Strobe Driver. The Strobe Driver is a transformer coupled gain stage. The Strobe Driver’s output is coupled to the Sampling Gate.

Sampling Gate. A power divider at the input of the amplifier routes 50% of the 1st LO’s output to another power divider. One port of the second divider is reserved for Option 15 and is terminated in 50 Ω. The other port is coupled to the Sampling Gate.

If the output frequency of the 1st LO were stable, LO sampling would occur at the same level since the rate at which the LO output is sampled is constant. However, the LO output has a tendency to drift slightly under certain conditions, such as unstable ambient temperature. Consequently, sampling occurs at different levels, resulting in a beat note. Thus, the BEAT NOTE signal is a measure of the 1st LO’s drift.

Reference Oscillator

The output of the Sampling Gate is routed to the Phase Lock Center Frequency Control (PLCFC) module.

The Reference Oscillator board provides a 100 MHz frequency reference and amplitude reference for the Spectrum Analyzer. The frequency reference enables the high counter accuracy.

Firmware based routines use the Amplitude Calibrator output as a reference for calibrating internal gain settings.

The Reference Oscillator consists of the following blocks of circuitry:

H Power Supply Regulation

H Heater

H Oscillator

H Distribution

H Amplitude Calibrator

3- 16

H Microprocessor Interface

2715 Spectrum Analyzer Service Manual

Theory of Operation

Figure 3--8 is a block diagram of the Reference Oscillator section.

Heater

DATA0

RFLATCH

CLK0

DATAI

CLKI

Microprocessor

Interface

Output

Buffer

Input

Buffer

Output

Buffer

100 MHz

Oscillator

CAL Enable

Distribution

CAL Enable

+5 V

Amplitude Calibrator

RF UP CFC

Spare

100 MHz

@--22 dBm

+10 V

+5 V

−11 V

Figure 3- 8: Reference Oscillator Diagram

Power Supply Regulation. The Oscillator and the Amplitude Calibrator are

furnished with stringent, on board, power supply regulation to minimize power supply ripple. Otherwise, both the Oscillator and the Amplitude Calibrator would produce FM sidebands proportional to power supply ripple amplitude and frequency.

Crystal Heater. The Crystal Heater maintains the oscillator crystal’s case temperature within a 3° window of the crystal’s operating temperature (near 70° C) over the instrument’s operating temperature range. The crystal leads sink heat such that the crystal inside the case operates at temperatures below the case temperature.

Power Supply Regulation

2715 Spectrum Analyzer Service Manual

3- 17

Theory of Operation

The heater circuit maintains a constant 15 V potential across the heater element regardless of power supply ripple. The circuit is shown in Figure 3--9.

+5 V

10 kΩ

22.1 kΩ

−11 V

10 kΩ

−

22.1 kΩ

27.4 kΩ

6.91 kΩ

−11 V

−

10 kΩ

1kΩ

+5.2 V

2.5 Ω

Heater

-- 1 1 V

Figure 3- 9: Crystal Heat er and 15 V Regulation Circuit

Oscillator. The oscillator generates the 100 MHz reference frequency that is used

by the instrument firmware to enhance frequency accuracy. Figure 3--10 shows the AC equivalent for the oscillator. At resonance, the tank inductor and capacitor Lt and Ct exhibit an open circuit condition, and the LC equivalent of the crystal (Lm and Cm) exhibit a short circuit condition. Thus, at resonance, the open loop gain is calculated as:

3- 18

A =

(re1+ re2+ rs)

This gain must be greater than unity to ensure oscillation.

2715 Spectrum Analyzer Service Manual

re1≈ 8.3Ω

82.5 Ω

Theory of Operation

+5 V

221 Ω

re2=5.7Ω

rs=50Ω

Figure 3- 10: Oscillator AC Equivalent

At oscillation, the loop gain is unity and the phase 0°. If the phase delay of Q1, Q2, or the tank changes, the operating frequency must also change to maintain a 0° loop phase shift. Because of this phase/frequency shift dependency, the Q of the parallel tank circuit is made as low as possible to minimize the tank phase change as the values of Lt and Ct drift.

The component values of the tank circuit are determined by the voltage swing at the collector of Q2 (Figure 3--11). The collector of Q2 drives an ECL line receiver. Therefore, the collector voltage should swing 1 V peak to peak about 3.8 VDC (3.8 V being the ECL Vbb bias voltage). The gain of Q2 is calculated as:

A =

(re1+ re2+ rs)

= 3

2715 Spectrum Analyzer Service Manual

3- 19

Theory of Operation

0.1 f

−8.8 V

3.92 kΩ

47.5 Ω

3.92 kΩ

1kΩ

≈ 8.3 Ω

82.5Ω

20 nH

rs<50 Ω

47.5 Ω

82 pf

+5 V

≈ 5.7 Ω

1.5 kΩ

−8.8 V

Figure 3- 11: Oscillator DC Equivalent

The voltage swing required across the tank circuit must be at least equal to the ratio of 1 V to the calculated gain, which is 0.3 V. If the bias current available in Q1 is 3.6 mA, then the tank resistance required is calculated to be:

0.3 V

3.6 mA

= 83 Ω

Distribution. The distribution circuit represents an ECL line receiver. This circuit receives the 100 MHz signal from the Oscillator and steers it to the following circuits at --4 dBm.

H RF Mother Board (2nd and 3rd LOs)

H Microprocessor (Counter Section)

H CFC Board (1st LO Phase Lock)

H Port reserved for future option

3- 20

H Amplitude Calibrator on the Reference Oscillator board

Amplitude Calibrator. The Amplitude Calibrator receives a 100 MHz signal from the distribution circuit. The level of the 100 MHz signal is adjusted, and the resultant calibrator signal is then routed to a switch on the Step Attenuator board.

When enabled by the Microprocessor, a differential pair of transistors switch a carefully controlled current on and off across a 56.2 Ω resistor. The resulting signal, with a --22 dBm level, is routed to the calibrator port through an 8 dB pad.

2715 Spectrum Analyzer Service Manual

Theory of Operation

Microprocessor Interface. The Microprocessor Interface is used by the Microprocessor board to communicate with the Reference Oscillator board. An 8 bit input shift register controls the operation of the board, and an 8 bit output shift register contains frequency correction bits for indicating the Oscillator frequency. The microprocessor clocks (CLKO) eight bits of serial data (DATAO) into the input serial register, and it then latches the serial contents (RFLATCH--) to the parallel outputs. The microprocessor clocks data out of the output register by setting bit 7 of the input register low to enable the Buffer (see Figure 3--8 on page 3--17) and using CLKI-- to clock serial DATAI out. Refer to Table 3--1 for the bit mapping of the registers.

Bit 0 of the input register is the last bit to leave the microprocessor, and bit 0 of the output register is the last bit to reach the microprocessor.

Bit 0 of the input register enables the calibrator signal when high and disables it when low. Bit 7 of the input register allows the microprocessor to read the contents of the output register when set low, and it tristates the output buffer when set high.

Table 3- 1: Input and Output Bit Definition

Input Register Output Register

Bit Function Bit Function

0 Cal Enable 0 CB0 1

1 None 1 CB1 2

2 None 2 CB2 4

3 None 3 CB3 8

4 None 4 CB4 16

5 None 5 CB5 32

6 None 6 CB6 64

7 Output Enable 7 CB7 128

The output register has 8 bits available to represent the Oscillator frequency. The microprocessor can then read the Oscillator frequency through these bits to within 10 Hz. The possible values are 1 through 254. The microprocessor interprets a value of 128 as a frequency of 100 MHz, 127 as 99,999,990 Hz, 129 as 100,000,010 Hz, and so forth.

Values 0 (all bits low) and 255 (all bits high) are used to send a hardware failure message to the microprocessor.

Phase Lock Assembly (Center Frequency Control System)

There are three major operating areas of the frequency control system:

2715 Spectrum Analyzer Service Manual

3- 21

Theory of Operation

In wide spans (5.1 MHz/div or greater), the center frequency is set coarsely by setting a suitable bias current in the main coil. Fine increments of the center frequency are set by appropriate currents to the FM coil. In this mode, sweeping over the span is accomplished by summing a suitably scaled analog sweep signal with the drive to the main coil. The strobe signal is not even turned on except briefly when needed to assist in verifying the exact 1st LO frequency by counting the beat frequency.

In moderate spans (50 kHz/div through 5 MHz/div), sweeping is done by summing the scaled sweep signal with the drive to the FM coil. Additionally, a noise suppressing low pass filter is inserted into the main coil circuit to reduce residual FM and phase noise due to noise from the main coil driver. Otherwise, the setup is the same as for wide spans. In this mode, the strobe is unused except when counting the 1st LO frequency.

When operating in narrow spans (20 kHz/div and less), the 1st LO is phase locked to a harmonic of the strobe frequency. Coarse control of the center frequency is effected by choosing which harmonic of the strobe frequency is used (by setting an appropriate main coil current before commanding the hardware to lock). Sweeping and fine control of center frequency are done by controlling the strobe frequency. When phase locked, the FM coil is used by the loop to adjust the 1st LO to zero phase error.

Power Supply Regulation

PLCFC Module Functional Blocks. The Phase Lock Center Frequency Control (PLCFC) module circuitry can be grouped into the following functional areas:

H Power Supply Regulation

H 1st LO Coil Drivers for the Current Source

H Strobe Frequency Generator (VCO Module)

H 1st Phase Lock Loop and Beat Note Processor

H Signal Path and Switching Summary

H Digital to Analog Conversion

H Digital Interface

There are six regulated supplies on the PLCFC circuit board and two additional regulators in the VCO module.

- 5 V Reference Supply (- 5 VREF). This is a precision reference supply for those circuit applications where a critical frequency is directly dependent on a voltage or current.

3- 22

2715 Spectrum Analyzer Service Manual

Theory of Operation

This supply consists of VR160, U166, U174, Q170, Q674, and associated components. VR160 is a temperature compensated reference diode that defines the output voltage. U166 and Q170 constitute a buffered scaling amplifier to provide the desired --5 V output at sufficient current. C660 makes the closed loop bandwidth very low to minimize noise from the reference diode on the output. U174 and Q674 convert --5 V to +10 V to provide stable low noise current to the reference diode through R171. The +8.5 V path through CR175 is used to guarantee start up of the supply. CR175 disconnects the potentially noisy start up source once the emitter of Q674 goes sufficiently positive.

- 5 V Supply. This supply is not to be confused with the --5 V Reference Supply.

This supply is regulated by U470 and serves solely as a reference for the remaining four supplies on the board. U470 is a programmable shunt regulator whose output voltage is defined by an internal reference and by R472 and R473.

+8.5 V Supply. U282A and Q781 constitute a buffered operational amplifier used in the inverting configuration to provide +8.5 V from an input of --5 V. (Note that Q781 provides a phase inversion, so the polarities of the operational amplifier IC input pins have to be reversed from the usual practice.)

1stLO Coil Drivers

Current Source

+15 V Supply. U380B and Q880 operate in the same fashion as the corresponding parts in the +8.5 V regulator.

- 8.5 V Supply. U282B and Q780 serve as a buffered operational amplifier in the non inverting configuration to provide --8.5 V.

+5 V Supply. U380A and Q881 serve as a buffered operational amplifier used in an inverting configuration to provide +5 V. (Note that Q881 is used in noninverting fashion, so that the normal polarities of the operational amplifier IC terminals apply here.)

The regulators in the VCO module will be discussed later in this section on page 3--25.

It is desirable to drive the 1st LO coils from high impedance sources so that temperature dependent changes in winding resistance have negligible effect on stability.

Main Coil Driver. U921 and Q521 constitute a buffered operational amplifier used in an inverting configuration. Inputs to the summing junction are from a number of sources and all pass through Q920. R900 (a current sense resistor in the return lead of the main coil) develops a voltage proportional to main coil current.

2715 Spectrum Analyzer Service Manual

3- 23

Theory of Operation

This voltage across R926 defines the feedback current to the summing junction of the operational amplifier. This circuit forces 1st LO main coil current to be proportional to the sum of the currents from the various control sources, which is described later. The normal operating current range of the main coil is from approximately 135 mA to 255 mA.

Q920 is a switch that is normally conducting and consequently has no significant impact on circuit operation as described. However, it is sometimes necessary to momentarily set the main coil current to zero in order to standardize frequency errors due to hysteresis in the 1st LO magnetic structure. When this is desired, the microprocessor asserts the DEGAUSS line HIGH (by way of the digital interface circuits), which causes Q931 and Q930 to pull the gate of Q920 to

--8.5 V. This opens the switch, disconnecting the normal input and feedback paths of the circuit. R929 provides a slight negative feedback in this situation, ensuring that the main coil current goes to zero instead of to some undefined value.

The main coil current is the sum of at least two items. First, there is a large fixed bias current stemming from the reference supply and R923 (trimmed by R931 and U920) to set the 1st LO at 3.01 GHz in the absence of other inputs. Second, there is a current induced by DAC U950A (and subsequent circuits), which is used to steer the 1st LO over the range from 2.11 to 3.91 GHz (2.11 to 4.26 GHz for Option 50 and Option 75). This current is normally a steady state value selected by the microprocessor to coarsely set the center frequency. Third, if the instrument is set to a span greater than 5 MHz/div, there is a sawtooth sweep waveform summed into the main coil current through switch U830A. This corresponds to the wide span operating mode discussed earlier in the Block Diagram description.

3- 24

FM Coil Driver. U811 and U810 together form a buffered operational amplifier

used in the inverting configuration. Input currents to the summing junction come from a variety of sources, to be described later. R905 is the current sense resistor for the FM coil. The voltage developed across it results in the current fed back to the summing junction through R815. Thus, this circuit forces a current through the FM coil proportional to the sum of the various control currents put into the summing junction. The normal current range for the FM coil is from approximately --120 mA to +120 mA.

Q910 and Q911 serve as a low resistance switch. When closed (gates held several volts positive), the FM coil driver operates as described above. When open (gates held several volts negative), the driver is disconnected and the FM coil gets its current from R714, which is the situation when the instrument is phase locked. Control of the switch state is through Q703 and Q800 from the signal PLLCON--. This signal is LOW when the instrument is phase locked. Several other switches are also controlled by the same command. R812 keeps U811 out of saturation when the switch is open.

2715 Spectrum Analyzer Service Manual

Theory of Operation

When the FM coil driver is in use (instrument not phase locked) there are two potential signal sources summed into the driver circuit. One that is always present is induced by DAC U850A and subsequent circuits. It is steered into U821 by switch U757A, and serves to finely set the center frequency. The other is selected only in moderate spans. It is the sawtooth sweep waveform used to sweep the 1st LO over spans ranging from 50 kHz/div through 5 MHz/div.

Strobe Frequency

Generator (VCO Module)

Functionally, this module is a voltage controlled frequency source. It has an output frequency range from 25.73 MHz through 26.05 MHz in response to a tuning voltage range of approximately 4 V to 12.5 V. There is also a switch to select which of two signals is counted by the microprocessor, and there are means to turn off the output.

The strobe frequency comes from a VCO that ranges from 102.9 MHz through

104.2 MHz and whose output frequency is divided by four to yield the desired strobe frequency. Its frequency is controlled by phase locking it (with a 100 MHz offset) to 1/4 the frequency of a free running VCO (the LFVCO) that operates over a frequency range of 11.68 MHz through 16.84 MHz. It is this LFVCO that is actually tuned by the incoming tuning voltage referred to earlier, and this phase locked loop within the VCO module is called the inner loop. The strobe signal is generated in this manner in order to control close in phase noise and to provide a countable signal (the LFVCO output) whose frequency is not condensed into a very narrow range that would require long times to count to adequate resolution.

The LFVCO consists of Q426, T430, varactors CR532 and CR540, and associated components. Output (from the collector of Q422) is made available for external counting through selector switch U240. The LFVCO output frequency is also divided by four through U410, and the result is the reference frequency for the inner loop. U512 and U510 serve as a phase/frequency detector for the inner loop. The differential output of the phase detector is passed through error amplifier U435 and becomes the tuning voltage for the HFVCO.

The HFVCO consists of Q522, L610, varactor CR511, trim capacitor C611, and associated parts. Output is taken from a tap on L610, then split through a pair of isolation amplifiers (Q400 and Q410 plus Q316). Output from Q400 is divided by four in U300, providing the useful strobe frequency output of the module. HFVCO output from Q316 is applied to one input of mixer U320, whose other input is supplied with 100 MHz energy from the Reference Oscillator. The useful output of the mixer is the difference frequency between the HFVCO (for example, 103 MHz) and the 100 MHz reference, or 3 MHz. This signal is amplified (by Q310, Q312, and so forth.) and applied to the remaining input of the phase/frequency detector, thus closing the inner loop.

U240 serves two functions; both controlled by the logic signals CNTSELA and CNTSELB. First, it allows turning the HFVCO on or off by means of Q425. When the oscillator is turned off, Q101 is turned on at the same time to shut

2715 Spectrum Analyzer Service Manual

3- 25

Theory of Operation

down the strobe driver amplifier in the 1st LO BUFFER module.

Also, U240 serves as a count selector switch. It selects either the LFVCO signal or the 1st LO beat signal (from the PLCFC board) for counting by the microprocessor. R241 is part of a TTL to ECL level shifter, the remainder of which is located on the microprocessor board.

U510B provides a lock status indicator for the inner loop so that a lock failure can interrupt the microprocessor through circuitry on the PLCFC board.

The HFVCO receives supplementary power supply regulation by means of U122.

The LFVCO receives supplementary power supply regulation by means of U123, Q223, and associated parts.

1stLO Phase Lock Loop

(Outer Loop) and Beat

Note Processor

The output of the phase gate in the 1st LO Buffer module may either be a beat note (when loop is unlocked) or a phase error voltage for maintenance of lock. Thus, the output of the phase gate is split into two paths.

Beat signals in the range of approximately 3 kHz through 11 MHz are passed through a chain including U614, a low pass filter, U723, and U720. They drive a Schmitt trigger circuit (Q630 through Q633), which produces a clean rectangular wave at TTL levels. The desired beat note, noise, and one or more weak, extraneous beat notes arising from 1st LO harmonics mixing with other harmonics of the strobe frequency, will normally be within the pass band of the low pass filter. The level control, R620, sets the overall signal level so that only the desired beat note is strong enough to overcome the hysteresis designed into the Schmitt trigger. The Schmitt trigger output may be routed to the microprocessor through a selector switch on the VCO module.

Phase error information from DC through a few hundred kHz is passed through U606 and switch U700D (when phase lock is invoked) to error amplifier U713. The output of U713 is applied to the FM coil through R714. When phase lock is invoked by setting PLLCON to high, U700D is closed and U700C is opened, closing the outer loop. Nominally, the loop bandwidth is set to 20 kHz. It may vary considerably from this value due to frequency dependent variations in the output level and slope of the phase gate. R709 provides for a known drift direction of the 1st LO tuning when the loop is first closed, but the initial frequency is away from lock. The instrument firmware purposely sets up a significant frequency offset in the direction that allows the loop to drift into lock, as a way of dealing with uncertainties in starting conditions.

3- 26

The outer loop has a holding range of approximately ±2.5 MHz before U713 saturates. U650A and U650B form a window comparator that generates logic signals (either INCR MAIN or DCR MAIN) when the loop approaches a range limit so that the microprocessor can take corrective action (for example, changing the main coil current in the appropriate direction to recenter the loop).

2715 Spectrum Analyzer Service Manual

Theory of Operation

This allows for 1st LO drift or user changes to the center frequency setting without having to drop and reacquire lock for every change.

If Q652 is turned on by the signal UNLKIND (signifying that the inner loop is unlocked), both INCR MAIN and DCR MAIN are turned on simultaneously. This is a unique condition that the microprocessor interprets as a hardware failure in the VCO module.

Summary of Outer Loop Lock Acquisition. When the instrument is placed into a situation calling for phase lock operation, several things are done by the firmware to arrange for a lock at the correct frequency.

The N number (that is, the harmonic order of the strobe to which the 1st LO will lock) is calculated, and the strobe and corresponding VCO frequencies needed are calculated. The sweep is disconnected, the FM coil DAC is set to mid range (FM coil current to nominal zero), and the main coil DAC is set to the value that will place the 1st LO as close as possible to the desired 1st LO frequency (it can be several hundred kHz off because of the coarseness of the main coil DAC steps). Now the VCO is tuned by trial and error so that the strobe line, at a frequency of N X F

strobe, is approximately 100 kHz above the actual 1st LO

frequency (that is, the measured beat frequency is 100 kHz on the correct side of zero beat). Then, lock is invoked by setting PLLCON high. Due to the intentional offset provided by R709, the 1st LO drifts rapidly into lock. After a suitable delay, acquisition of lock is verified by checking the states of both lock limit comparators and by checking that the beat frequency is zero.

Signal Path and Switching

Summary

At this point the loop is locked, but in the wrong spot. Now the microprocessor proceeds to tune the VCO (and consequently, the strobe and 1st LO) to the correct frequency by repeatedly tuning and counting the VCO. The sweep is then switched into the VCO tuning voltage, and the instrument is now scanning the desired spectrum range.

Wide Span Operation (5.1 MHz/div and Higher Spans). TheMaincoilisdrivenbya fixed bias summed with DAC U950A output and a sweep signal (routed through U830A).

The FM coil is driven with VCFC FM arising from DAC U850A only (routed through U757A). Current is routed through Q910 and Q911 to the FM coil. See Figure 3--12.

2715 Spectrum Analyzer Service Manual

3- 27

Theory of Operation

Analog Sweep In

VOFS

Summing and Fixed

Scaling

Summing and Fixed

Scaling

Summing and Fixed

Scaling

VOFS

Main Coil

Driver

FM Coil

Driver

MAIN

FSTROBE

1st LO

Harm GenVCO Module

1st LO to 1st Converter

1st LO

Phase Gate

1st LO Beat to

Counter

Serial In

Serial Out

Microprocessor

DIG

SWP DAC

Main DAC

DAC

PLL

DAC

Decade

Atten

DIG

VREF

Figure 3- 12: Phase Lock Center Frequency Control Configuration for Wide Spans (Unlocked, Sweep Main Coil)

The VCO is not used except intermittently for frequency corrections, and it is tuned by a fixed bias summed with VCFCU arising from DAC U950B.

Moderate Span Operation (50 kHz/div through 5 MHz/div Span). The Main coil is driven by a fixed bias plus a DAC output (U950A).

The FM coil is driven with VCFC FM arising from DAC U850A (routed through U757A) summed with the sweep signal (routed through U830B). Total current is routed through Q910 and Q911 to FM coil. See Figure 3--13.

3- 28

2715 Spectrum Analyzer Service Manual

Analog Sweep In

Theory of Operation

VOFS

Summing

and Fixed

Scaling

Summing

and Fixed

Scaling

Summing

and Fixed

Scaling

VOFS

Main Coil

Driver

FM Coil

Driver

MAIN

FSTROBE

1st LO

Harm GenVCO Module

1st LO to 1st Converter

1st LO

Phase Gate

1st LO Beat to

Counter

Serial In

Serial Out

Microprocessor

DIG

SWP DAC

Main DAC

DAC

PLL

DAC

Decade

Atten

DIG

VREF

Figure 3- 13: Phase Lock Center Frequency Control Configuration for Moderate Spans (Unlocked, Sweep FM Coil)

The VCO is not used except intermittently for frequency corrections and is tuned by a fixed bias summed with VCFCU arising from DAC U950B.

Narrow Span Operation (20 kHz/div and Smaller Spans). The instrument is phase locked.

The Main coil is driven with a fixed bias summed with DAC U950A output. See Figure 3--14.

2715 Spectrum Analyzer Service Manual

3- 29

Theory of Operation

Analog Sweep In

VREF

Summing

and Fixed

Scaling

Summing

and Fixed

Scaling

VREF

Main Coil

Driver

VCO Module (Strobe Gen)

Lock Limits

Comparator

Main

FSTROBE

1st LO

Harm Gen

Phase Gate

Error Amp &

Loop Filter

1st LO to 1st Converter

N-F Strobe

1st LO

Serial In

Serial Out

Microprocessor

DIG

SWP DAC

Main DAC

DAC

PLL

DAC

Decade

Atten

DIG

VREF

Figure 3- 14: Phase Lock Center Frequency Control Configuration for Narrow Spans (Locked, Sweep VCO)

The FM coil is driven with the output of the phase lock error amplifier, U713, only.

1st LO Beat to

Counter for Lock

Verification

Phase Error Voltage

Digital to Analog

Conversion

The VCO is active continuously and is tuned by a fixed bias summed with VCFCU from DAC U950B, VCFC L from DAC U850A (routed through U757D), and sweep voltage VSWP PLL (routed through U757B).

The PLCFC board has four 12 bit DACs in two IC packages, U850 and U950.

On the digital side, each package has four data lines, three address lines, and two control lines. The DACs contain internal registers for the 12 bit words associated with each analog output and, therefore, the microprocessor must write multiple 4 bit words to a package in order to set up a new output.

These are multiplying DACs. Each delivers an output current that is the product of an analog voltage (called the reference) and the 12 bit digital word. These units can correctly deal with either polarity of reference voltage. Three of them (U850A, U950A, and U950B) are supplied fixed reference voltages and serve simply as computer controlled DC sources.

DAC U850A is called the FM DAC but serves two roles. In non phase locked spans, its output ultimately ends up fine tuning the 1st LO center frequency through the FM coil.

3- 30

2715 Spectrum Analyzer Service Manual

Theory of Operation

In phase locked spans, its output is used to fine tune the VCO frequency. In either case its output passes through U852, which has an output range of 0 to +5 V. U845 sums that with an offset and provides gain so that the output of U845 ranges from --5 V to +5 V. This signal is called VCFC (L/FM) and is routed to the appropriate destination by U757A and U757D.

Main Coil DAC U950A output passes through U952 and U940. U940 provides gain such that the output of U845 ranges from --5 V to +5 V, and the result is summed with the other components of the main coil current. Its function is coarse tuning of the 1st LO center frequency, in steps of approximately 400 kHz.

U950B is the PLL DAC. Its function is coarse tuning of the VCO frequency. Its output is converted to the --5 V to +5 V range by U954 and U941 before being summed with the other components of the VCO tune voltage.

Unlike the other DACs, U850B’s reference input is supplied with the analog sweep waveform SWP (from the Sweep board through U565) and serves as a microprocessor controlled gain control to determine span/div. Its output passes through U854 to a decade attenuator composed of U831 and associated components. The output of the decade attenuator is then routed to the desired destination by switches U830A, U830B, and U757B. In wide spans, this signal sweeps the 1st LO main coil. In moderate spans, it sweeps the 1st LO FM coil. In phase locked spans, it is used to sweep the VCO frequency.

Digital Interface

This circuitry links the phase lock hardware with the microprocessor. The link is bidirectional. Commands and DAC setting data are sent to the PLCFC module, and lock status information is sent back to the microprocessor. In addition, there is provision to loop input data back to the microprocessor to verify integrity of the interface circuitry .

The path into the PLCFC module is through a 24 bit shift register composed of U361, U460, and U560. Serial data on the DATAO line is shifted into the register by the clock signal CLKO. When all 24 bits have been shifted in, CFLATCH-- is used to latch data simultaneously from all shift register stages to parallel output registers. The resulting 24 bit parallel word is used to control switches, set DACs, and do a number of other things on the module. A listing of the 24 lines and their functions appears later in Table 3--22 on page 3--71.

CFCLATCH-- also triggers U372 causing a delayed pulse on the WR-- line, latching data into internal registers of the DACs.

U370 is an 8 bit shift register used for transferring data from the module back to the microprocessor. Serial data is shifted out on the DATAI line by the clock CLKI--, which is gated into the clock input of the register by U270C as controlled by CFCACK--. Data may be serially loaded into this register through the EXAM line coming from the tail end of the 24 bit input register. In this situation the data is clocked into the register by a derivative of CLKO, which is gated by LOADEXM through U270D.

2715 Spectrum Analyzer Service Manual

3- 31

Theory of Operation

This is the loop back path referred to earlier for checking the interface. This register may also be loaded with up to eight bits of parallel data for subsequent serial transfer to the microprocessor. Only three bits are used. Bits 7 and 8 are the signals (INCR MAIN and DCR MAIN) from the lock limits comparator, and bit 5 is wired to logic 1 as a board identity.

The gating of CLKI-- and CLKO into the output shift register (by CFCACK-and LOADEXM, respectively) is partly a matter of source selection and is also necessary because both clock signals are used by other boards in the system at some times.

Any transition on either INCR MAIN or DCR MAIN (or both) will load the new states of those lines into the output shift register. (The various sections of U360 serve as edge detectors to generate the load command to the shift register.) Further, if LKINTEN is high at the time, U471B will end up SET, interrupting the microprocessor by way of CFCREQ--. The line READEXM provides a direct method of setting the interrupt, if desired. Any transition on LKINTEN will also cause the shift register to be loaded, providing a forced means for checking the status of the lock lines at any time. The microprocessor uses CFCACK-- to clear U471 of the interrupt (in addition to the gating function mentioned above).

Summary of Digital Control Lines on Phase Lock Center Frequency

Control Module

READEXM. Low to high transition forces CFC interrupt.

LOADEXM. High level gates CLKO into output shift register clock input.

DEGAUSS. High level forces 1st LO main coil current to zero.

CNTSELA and CNTSELB. These signals are decoded to set state of selector switch in VCO module. Both high is strobe OFF. CNTSELA high and CNTSELB low is count VCO. CNTSELA low and CNTS ELB high is count beat frequency. Both low is strobe ON but no count selected.

PLLCON. High level commands phase lock configuration.

LKINTEN. High level enables interrupt on transition of either lock limit comparator line.

CAPCON. High level connects noise reduction capacitor across 1st LO main coil.

SWDECA. A and B are decoded to select setting of sweep decade attenuator . Both low is straight through. A high and B low is divide by 10. A low and B high is divide by 100. Both high is disconnect sweep.

SWSELA. A and B are decoded in U274 to operate switches that direct sweep waveform to proper destination.

3- 32

SWSELB. Both low is sweep main coil. A high and B low is sweep FM coil. A low and B high is sweep VCO. Both high is no sweep.

2715 Spectrum Analyzer Service Manual

A0, A1, and A2. Address lines for DAC internal register selection and control.

UPD. Used for simultaneous transfer to DAC output registers.

DB0’,dB1’,dB2’, and dB3’. Data lines for DAC U950 (A and B).

DB0, dB1, dB2, and dB3. Data lines for DAC U850 (A and B).

Variable Resolution Module

This section contains a detailed description of the Variable Resolution module.

Theory of Operation

Input Amplifier

The input amplifier used is a transformer feedback stage that provides approximately 12 dB of gain with 10 dB of reverse isolation. See Figure 3--15. The match at each port with the other terminated is better than 15 dB at 10 MHz. The noise figure is less than 3 dB and, with 12 mA flowing in the device, the output intercept is approximately +30 dBm. The match at each port is highly sensitive to a proper termination being presented to the other port.

2715 Spectrum Analyzer Service Manual

3- 33

Theory of Operation

10 MHz/−20 dBm from RF Mother Board

RF OPTIONS

1 MHz, 100 kHz, 10 kHz, 1 kHz,

and 300 Hz Filters

1010

1dBStep

PIN Diode Attenuator

10 MHz/−10 dBm

to Log Amp

5MHz

300 kHz

30 kHz

3kHz

Figure 3- 15: Variable Resolution Module Diagram

PIN Attenuator

The PIN attenuator design is based upon a pair of matched pin diodes used in a tee configuration. This configuration maintains the impedance match at each end, providing the product of the PIN diode resistances is equal to the square of the end terminations. This can be approximated if the sum of the currents in the PIN diodes is equal to a constant. The DAC has complementary current outputs whose total is set by an adjustment. The attenuation range is approximately 12 dB with a 1 dB minimum loss. The worst case return loss at the end points is 15 dB. The step size for an 8 bit DAC is 0.04 dB steps in the center of its range.

3- 34

2715 Spectrum Analyzer Service Manual

Theory of Operation

10 dB Gain Step Amplifier

1 dB Gain Step Amplifier

Routing Switches

The 10 dB gain step stages incorporate a transformer feedback amplifier. These stages have approximately 0.5 dB of loss or 9.5 dB of gain, for a net difference of 10 dB. When the gain step is selected, the signal is routed through the amplifier for a gain of approximately 11.5 dB. A pad of approximately 1.5 dB is added to trim the gain down to 10 dB. The signal is then routed through a switch that has approximately 0.5 dB of loss. When the amplifier is deselected, the signal is routed around the amplifier, thus preserving noise figure and intercept point. A total of five step gain stages are used.

The 1 dB gain step amplifier is the last amplifier before the filter switching tree. The amplifier is composed of a class AB, three stage, feedback amplifier. The gain is adjusted in 2 dB steps for a total of 10 dB. The 1 dB steps are done by shunting part of the signal to ground. This is controlled by Q246, located at the input of this amplifier. This configuration allows the entire 10 dB gain sequence to be contained within one step gain stage.

The routing switches are used to route RF signals to various areas. They are composed of a transistor in heavy saturation that has relatively large charge storage characteristics. The topology used is a shunt series configuration. These switches are used on both the input and output of each filter including the external filter connection.

RF Options

The RF Options is a system of additional resolution bandwidth filters that enhance the measurement capability of the instrument. See Figure 3--16.

2715 Spectrum Analyzer Service Manual

3- 35

Theory of Operation

10 MHz IF

from VR

1 MHz Filter 11.5 dB

100 kHz Filter 11.5 dB 11.5 dB

10 kHz Filter 11.5 dB

10 MHz IF

to VR

1 kHz Filter 11.5 dB

300 Hz Filter 11.5 dB 11.5 dB

Figure 3- 16: RF Options Diagram

3- 36

2715 Spectrum Analyzer Service Manual

Theory of Operation

The board provides the resolution bandwidths used to fill in between filter values installed within the Variable Resolution module. The bandwidth range is 1 MHz to 1 kHz in decade steps, and 300 Hz. Each filter path consists of a switchable amplifier and bandpass filter combination.

Control System Interface

Bandwidth Control

Identification Bit

Gain Stage

Routing Switches

The control of the RF Options by the microprocessor is through one 8 bit shift register. Data is shifted serially in one 8 bit word.

The variable bandwidth section consists of a switching tree to select one of five filters. Available bandwidth filters, in addition to those already in place in the Variable Resolution module, are 1 MHz, 100 kHz, 10 kHz, 1 kHz, and 300 Hz.

A resistor is installed between either pin 12 (d6) or pin 13 (d5) of shift register U390 and the base of Q396 to complete a path for an identification bit for the Microprocessor. This allows the Microprocessor to determine that the 300 Hz filter is installed on the RF Options board.

The gain stage used is a transformer feedback stage that provides approximately

11.5 dB of gain. In the case of the 100 kHz and 300 Hz filters, two gain stages are used. The impedance match at one port of the Gain Stage is highly sensitive to a proper termination being presented to the other port.

The routing switches are used to route RF signals to the selected bandwidth filter. They are composed of a transistor in heavy saturation that has relatively large charge storage characteristics. The topology used is a shunt series configuration. These switches are used on both the input and output of each filter. That is, the filters are switched in and out at both the input and the output so that when a filter is not being used it is effectively out of the circuit.

Each bandwidth filter is composed of a double tuned circuit (a two pole Butterworth filter section), an amplifier to provide gain correction and isolation, and another double tuned circuit. The intermodulation performance of the amplifier is less critical because the amplifier is placed after the filter. The noise power generated by the stage is reduced by placing a filter of equal bandwidth after the gain stage.

Diagnostics

2715 Spectrum Analyzer Service Manual

The identification bit can provide useful information on the proper configuration of the instrument.

3- 37

Theory of Operation

Log Amplifier

The Log Amplifier system is a high performance, intermediate amplifier system that provides display laws of linear detection and logarithmic detection of the incoming signal. The log display has scale factors of 10 dB/div, 5 dB/div, and 1 dB/div. The linear mode has the ability to magnify the top portion of the waveform to enhance the measurement capability. The module also contains an FM detector, which, when used with the built in audio amplifier, can be used to monitor the modulated input signal for enhanced signal identification. The audio amplifier can also be used to monitor the output of the displayed waveform regardless of the video source. There is an alternate audio input for the push button clicks generated by the system controller. This audio signal is also used for the vertical amplitude reference, to check the sweep speed, and for internal triggers. An amplitude limited output is available for the period counter for determining the actual frequency of the signal present in the IF system. External video inputs are provided for the use of external detectors and the rear panel. A provision is made for clamping the display when the 1st LO is tuned out-ofband. Frequency dependent amplitude (flatness) correction is also performed on this board.

Hardware

Flatness Error Correction

Noise Filter

The Log Amplifier system is configured by using a 4.5 by 8.75 circuit board mounted in the card cage. The Microprocessor interface is through three 8 bit shift registers.

The signal level at the Log Amplifier board (J190) for full screen deflection is

--10 dBm. The first stage of the Log Amplifier is an amplifier that provides gain between 18 dB and 24 dB, depending on the frequency of the 1st LO. The amplifier is adjusted such that the gain is 18 dB at low frequencies and is up to 24 dB at the high end of the frequency range, because the frequency dependent amplitude error is always greater at the higher frequencies. The feedback is adjusted by changing the amount of current flowing through PIN diodes CR290 or CR291. The correction voltage, SWPSLOPE, reflects the frequency of the 1st LO. Provision for a second correction voltage from a future Digital Signal Processing module is included. This second correction voltage, which provides an interpolated voltage, will be derived from a flatness table. At present, only SWPSLOPE is used.

The output of the first stage, a gain slope amplifier, is then fed to a two pole noise filter to limit the noise to 5 MHz and to provide two more poles of 5 MHz bandwidth resolution filtering. The output of this filter is then sent to the log stages through a set of jumpers so the signal can be broken for calibration purposes and buffer amplifier Q170 (in a common base configuration) to form an auxiliary IF output.

3- 38

2715 Spectrum Analyzer Service Manual

Theory of Operation

Logarithmic Amplifier

Stages

Synchronous Detector

Ripple Filter

The core of the logging stage is a pair of AD640s. The AD640 uses five cascaded limiting amplifiers to approximate a logarithmic response to an input signal of wide dynamic range and wide bandwidth. The two AD640s are used in a parallel/summing operation. The input signal to one AD640 is amplified by 25 dB with the CLC501. This is a current feedback operational amplifier that has a clamping circuit used to limit the output to a value set by an external voltage divider. The other AD640 is fed through a 25 dB attenuator. The difference in input amplitude for small signals is then 50 dB. There is not enough gain in the 75 dB path to cause the AD640 to limit on the input noise of the CLC501. Thus, the full dynamic range of both parts is realized. This topology eliminates the need for a narrow bandwidth noise filter.

In Lin mode, the signal envelope is extracted from the RF carrier by the use of a synchronous detector. This detector is basically a multiplier. Detection is accomplished by feeding a limited signal into one input and a sample of the RF signal into the other. Since the limited input is always considered equal to plus or minus one unit, only the polarity is important. The sample RF is then multiplied by plus or minus one. Since the RF is always in phase with the limited input, the product is always positive. Thus, demodulation is achieved.

The ripple filter is a six pole elliptic filter with a finite transmission zero at the 10 MHz IF frequency and another at approximately 19 MHz. The purpose is to remove any of the remaining 10 MHz component that may still exist. Because of the full wave rectification provided by the synchronous detector and the log cells, the 10 MHz component is attenuated by approximately 30 dB. This greatly reduces the requirements of the ripple filter. However, the signal is not always at 10 MHz. The widest bandwidth is 5 MHz, so there is still a significant requirement for ripple reduction as low as 5 MHz.

Video Filter/Scale Factor

2715 Spectrum Analyzer Service Manual

After the Ripple Filter, the signal is offset before being amplified to bring the equivalent of a full screen signal in log mode or linear mode to correspond to 0 V output. The out-of-band clamp is also done at this time to deflect the CRT beam into the bottom of the screen when the display is outside the frequency limits of the Spectrum Analyzer. Next, the video filter selector is chosen. The bandwidth of the vertical chain is approximately 5 MHz. Therefore, when a video filter path is chosen, the maximum bandwidth drops to approximately 1 MHz. This switching tree also multiplexes in the external signals from the rear panel or the FM Detector.

3- 39

Theory of Operation

Immediately following the Video Filters is the Scale Factor amplifier. The gain of the Scale Factor amplifier can be set to 1.1, 2.2, 5.5, or 11 corresponding to 10 dB/div, 5 dB/div, 2 dB/div, or 1 dB/div. The linear function is done with the gain set to 1.1.

FM Detector

Period Counter Signal

Audio Amplifier

Video Amplitude

Calibrator

System Reset

The AD834 (U350) is a four quadrant multiplier that is used as a quadrature detector for demodulation of FM signals. The audio output is sent to the audio amplifier selector and to the video input selector.

The limited output of one of the log cells is used to drive an isolation buffer (U630A). This signal is used to drive the period counter on the Microprocessor board for frequency measurements.

The TDA1013A is used as the audio amplifier for monitoring purposes, and as a means of providing feedback to the user from the microprocessor.

Microprocessor audio appearing at pin 22 of J7 is used to provide feedback to the operator for push button clicks and out of range or uncalibrated conditions. This signal is also used to provide a signal for calibrating the video amplifier and display storage. The sweep triggers are also tested by this signal.

At power on, the system reset line SYSRST-- on pin 4 of J7 goes low until the Microprocessor resets it. During this time, the control latch’s output enable line is held false and the outputs are in a high impedance state. This is used only by the mute bit. The pull up resistor will force a mute condition during this time, thus disallowing any extraneous noise from the speaker.

Display Storage

3- 40

The Display Storage board digitizes both vertical (LOGVID) and horizontal (SWP) signals and places this digitized information in nonvolatile RAM (NVRAM). Various state machines on the board then take this digitized data from the NVRAM and generate the horizontal and vertical signals which are sent to the deflection circuitry on the Power Supply board. In addition to displaying the digitized data, the Display Storage board also is used to display the readouts and place markers on the CRT .

The major features of the Display Storage board are:

H Digitize the LOGVID signal from the Log Board (8 bits)

H Digitally track the SWP signal from the Sweep Board (9 bits)

H Acquire and store up to four waveforms in RAM

2715 Spectrum Analyzer Service Manual

Theory of Operation

H Provides for the ability to place up to two markers on a displayed waveform

H Implement and display a B,C--Save A waveform

H Display readout information on the screen

H Provide up to 28 Kbytes of nonvolatile storage area

H Provide two different waveform acquisition modes: Max Peak and Min/Max

H Provide a Max Hold function

Control System Interface

The following sections show the bit maps for each of the control registers on the Display Storage board.

Mode Control Register 1. Mode Control Register 1 is located in I/O space, at location 0x0FA00. Mode Control Register 1 is a read/write register. Table 3--2 describes the Mode Control Register.

Table 3- 2: Mode Control Register 1

Bit Number

7 DSON_L Low Display Storage On

6 DISP--A_L Low Enables B,C--Save A Display

5 MAXHLD_L Low Enables max hold function

4 PEAKDIS_L Low Enables max peak function

3 HLF/FLL_L High Selects location of B,C--Save A display

2 ACQ_ON High Enables the acquisition system

1 RDZEN High Not used

0 DS_PROTECT High Not used

Mnemonic

Activity Level

Description

DSON_L. Enables the Display Storage board to display the digitized waveforms when low. When this signal is high, the analog trace is drawn on the CRT.

DISP--A_L. Invokes the B,C--Save A display on the CRT when low.

MAXHLD_L. Invokes the Max Hold algorithm for A and B waveforms when low. In this mode a given bin will only be updated when the new vertical data is greater than the stored vertical data.

2715 Spectrum Analyzer Service Manual

3- 41

Theory of Operation

PEAKDIS_L. In the Normal Mode this bit selects one of the two acquisition modes. Either the Max Peak, when low, or the Min/Max algorithm when high. In the Enhance Mode this bit is used in conjunction with the ACQM0 bit of Mode Control Register 2 to invoke Sample and Min Peak algorithms. See Table 3--3 below.

HLF/FLL_L. In the Normal Mode this bit selects one of two positions on the CRT screen to normalize the B,C--Save A display. When this bit is low, the B,C--Save A display will be normalized to the top of the CRT screen. When this bit is high, the B,C--Save A display will be normalized to the middle of the screen. In the Enhanced Mode this bit is used in addition to the POS1 bit in Mode Control Register 2. See Mode Control Register 2 below for more details.

ACQ_ON. This bit asynchronously enables/disables the storing of vertical data into the waveform memory. When this bit is high, the vertical data will be stored in waveform memory. When this bit is low, the vertical data will not be stored in waveform memory. It is important to understand that the A/D converter is still running and the vertical data processing sections are still running. All that this bit does is control the ability to store the vertical data after being processed.

RDZEN. This bit is not used in the Display Storage board.

DS_PROTECT. This bit is not used in the Display Storage board.

Mode Control Register 2. Mode Control Register 2 is located in I/O space, at location 0x0FA04. Mode Control Register 2 is a read/write register.

In order to write to this register, it must first be enabled by setting the MCREG2 bit (bit 7) of the Scroll Register high. If at any time the MCREG2 bit is cleared (set low) Mode Control Register 2 will be cleared and disabled.

Table 3- 3: Mode Control Register 2

Bit Number

7 Not used

6 Not used

5 Not used

4 Not used

3 Not used

2 ENB2715 High Enables features available in 2715 instrument

Mnemonic

Activity Level

Description

3- 42

1 POS1 High MSB of B,C--Save A waveform position

0 ACQM0 High LSB of acquisition mode control

ENB2715. This bit, when high, enables the Enhanced Mode of the board.

2715 Spectrum Analyzer Service Manual

Tektronix 2715 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

WARRANTY

Table of Contents

List of Figures

List of Tables

General Safety Summary

Service Safety Summary

Preface

Contacting Tektronix

Specifications

Electrical Characteristics

Operating Information

Instrument Description

Conformance to Industry Standards

Product Service

Instrument Construction

Installation and Preparation for Use

Power Cord

Replacing the Fuse

Selected Components

Assembly and Circuit Numbering

Accessories

Menus

SWP/TRG Menu Structure

UTIL Menu Structure (1 of 2)

UTIL Menu Structure (2 of 2)

MRK/FREQ Menu Structure

CATV/APPL CATV Measurements Page 1 Menu Structure (1 of 3)

CATV/APPL CATV Measurements Page 1 Menu Structure (2 of 3)

CATV/APPL CATV Measurements Page 1 Menu Structure (3 of 3)

CATV/APPL CATVMeasurements Page 2 Menu Structure (1 of 2)

CATV/APPL CATV Measurements Page 2 Menu Structure (2 of 2)

CATV/APPL Applications Menu Structure

DEMOD Menu Structure

DSPL Menu Structure

USERDEFMenuStructure

INPUTMenuStructure

Theory of Operation

Block Diagram Description

Center Frequency Control

1stLO Buffer

Sweep

Display System

Circuit Description

Attenuator and 1stConverter

RF Mother Board and Phase Locked 2nd LO

Reference Oscillator

Phase Lock Assembly (Center Frequency Control System)

Variable Resolution Module

RF Options

Log Amplifier

Display Storage