Rohde and Schwarz FSP40 Operating Manual

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➢

Operating Manual

Spectrum Analyzer

R&S® FSP3

1164.4391.03

R&S® FSP7

1164.4391.07

R&S® FSP13

1164.4391.13

Printed in Germany

R&S® FSP30

1164.4391.30/.39

R&S® FSP31

1164.4391.31

R&S® FSP40

1164.4391.40

1164.4556.12-03-

Test and Measurement Division

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R&S

is a registered trademark of Rohde & Schwarz GmbH & Co. KG

Trade names are trademarks of the owners

1164.4556.12 0.2 E-2

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Certificate No.: 2003-22, Page 1

This is to certify that:

Equipment type Stock No. Designation

FSP3 1164.4391.03 Spectrum Analyzer FSP7 1164.4391.07 FSP13 1164.4391.13 FSP30 1164.4391.30 FSP31 1164.4391.31 FSP40 1164.4391.40

EC Certificate of Conformity

complies with the provisions of the Directive of the Council of the European Union on the approximation of the laws of the Member States

- relating to electrical equipment for use within defined voltage limits (73/23/EEC revised by 93/68/EEC)

- relating to electromagnetic compatibility (89/336/EEC revised by 91/263/EEC, 92/31/EEC, 93/68/EEC)

Conformity is proven by compliance with the following standards:

EN61010-1 : 2001-12 EN55011 : 1998 + A1 : 1999 EN61326 : 1997 + A1 : 1998 + A2 : 2001 + A3 : 2003

For the assessment of electromagnetic compatibility, the limits of radio interference for Class B equipment as well as the immunity to interference for operation in industry have been used as a basis.

Affixing the EC conformity mark as from 2003

ROHDE & SCHWARZ GmbH & Co. KG Mühldorfstr. 15, D-81671 München

Munich, 2006-11-07 Central Quality Management MF-QZ / Radde

1164.4391.01-s1- CE E-6

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Certificate No.: 2003-22, Page 2

This is to certify that:

Equipment type Stock No. Designation

FSP-B3 1129.6491.02 Audio Modulator AM/FM FSP-B4 1129.6740.02 OCXO 10 MHz FSP-B6 1129.8594.02 TV-Trigger FSP-B9 1129.6991.02 Tracking Generator FSP-B10 1129.7246.02 External Generator Control FSP-B15 1155.1006.02 Pulse Calibrator FSP-B16 1129.8042.03 Lan Interface 10/1000 Base T FSP-B20 1155.1606.02/.06 Extended Environmental Spec FSP-B21 1155.1758.02 LO/IF Connections FSP-B25 1129.7746.02 Electronic Attenuator FSP-B28 1162.9915.02 Trigger Port FSP-B29 1163.0663.07/.30/.40 20 Hz Frequency Extension FSP-B30 1155.1158.02 DC Power Supply FSP-B31 1155.1258.02 NIMH Battery Pack and Charger FSP-B32 1155.1506.02 Spare Battery Pack (NIMH) FSP-B70 1157.0559.02 Demodulator HW and Memory Extension

EC Certificate of Conformity

complies with the provisions of the Directive of the Council of the European Union on the approximation of the laws of the Member States

- relating to electrical equipment for use within defined voltage limits (73/23/EEC revised by 93/68/EEC)

- relating to electromagnetic compatibility (89/336/EEC revised by 91/263/EEC, 92/31/EEC, 93/68/EEC)

Conformity is proven by compliance with the following standards:

EN61010-1 : 2001-12 EN55011 : 1998 + A1 : 1999 EN61326 : 1997 + A1 : 1998 + A2 : 2001 + A3 : 2003

Affixing the EC conformity mark as from 2003

ROHDE & SCHWARZ GmbH & Co. KG Mühldorfstr. 15, D-81671 München

Munich, 2006-11-07 Central Quality Management MF-QZ / Radde

1164.4391.01-s2- CE E-6

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R&S FSP Tabbed Divider Overview

Tabbed Divider Overview

Safety Instructions are provided on the CD-ROM

Tabbed Divider

Documentation Overview

Chapter 1: Putting into Operation

Chapter 2: Getting Started

Chapter 3: Manual Control

Chapter 4: Instrument Functions

Chapter 5: Remote Control – Basics

Chapter 6: Remote Control – Description of Commands

Chapter 7: Remote Control – Programming Examples

Chapter 8: Maintenance and Instrument Interfaces

Chapter 9: Error Messages

Index

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Tabbed Divider Overview R&S FSP

Documentation Overview

Quick Start Guide R&S FSP

This manual is delivered with the instrument in printed form and in PDF format on the CD. It provides the information needed to set up and start working with the instrument. Basic operations and basic measurements are described. Also a brief introduction to remote control is given. More detailed descriptions are provided in the Operating Manual. The Quick Start Guide includes general information (e.g. Safety Instructions) and the following chapters:

Chapter 1 Front and Rear Panel

Chapter 2 Preparing for Use

Chapter 3 Firmware-Update and Installation of Firmware Options

Chapter 4 Basic Operation

Chapter 5 Basic Measurement Examples

Chapter 6 Brief Introduction to Remote Control

Appendix A Printer Interface

Appendix B LAN Interface

Appendix C External Generator Control

Operating Manual R&S FSP

This manual is a supplement to the Quick Start Guide and is available in PDF format on the CD delivered with the instrument. To retain the familiar structure that applies to all operating manuals of Rohde&Schwarz Test & Measurement instruments, the chapters 1 and 3 exist, but only in form of references to the corresponding Quick Start Guide chapters.

The manual describes the following models and options of Spectrum Analyzer R&S FSP. Options that are not listed are described in a separate manual. These manuals are provided on the CD ROM.

• FSP3 (9 kHz to 3 GHz)

• FSP7 (9 kHz to 7 GHz)

• FSP13 (9 kHz to 13.6 GHz)

• FSP30 (9 kHz to 30 GHz)

• FSP31 (9 kHz to 31 GHz)

• FSP40 (9 kHz to 40 GHz)

• Option FSP-B3 (audio demodulator)

• Option FSP-B4 (OCXO - reference oscillator)

• Option FSP-B6 (TV and RF trigger)

• Option FSP-B9 (tracking generator)

• Option FSP-B10 (external generator control)

• Option FSP-B15 (pulse calibrator)

• Option FSP-B16 (LAN interface)

• Option FSP-B20 (extended environmental spec)

• Option FSP-B21 (ext. mixer)

• Option FSP-B25 (electronic attenuator)

• Option FSP-B28 (trigger port)

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R&S FSP Tabbed Divider Overview

The operating manual is subdivided into the following chapters:

Chapter 1 Putting into Operation

see Quick Start Guide chapters 1 and 2

Chapter 2 Getting Started

gives an introduction to advanced measurement tasks of the R&S FSP which are explained step by step.

Chapter 3 Manual Control

see Quick Start Guide chapter 4

Chapter 4 Instrument Functions

forms a reference for manual control of the R&S FSP and contains a detailed description of all instrument functions and their application.

Chapter 5 Remote Control - Basics

describes the basics for programming the R&S FSP, command processing and the status reporting system.

Chapter 6 Remote Control - Description of Commands

lists all the remote-control commands defined for the instrument.

Chapter 7 Remote Control - Programming Examples

contains program examples for a number of typical applications of the R&S FSP.

Chapter 8 Maintenance and Instrument Interfaces

describes preventive maintenance and the characteristics of the instrument’s interfaces.

Chapter 9 Error Messages

gives a list of error messages that the R&S FSP may generate.

Index contains an index for the chapters 1 to 9 of the operating manual.

Service Manual - Instrument

This manual is available in PDF format on the CD delivered with the instrument. It informs on how to check compliance with rated specifications, on instrument function, repair, troubleshooting and fault elimination. It contains all information required for repairing the R&S FSP by the replacement of modules. The manual includes the following chapters:

Chapter 1 Performance Test

Chapter 2 Adjustment

Chapter 3 Repair

Chapter 4 Software Update / Installing Options

Chapter 5 Documents

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Tabbed Divider Overview R&S FSP

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R&S FSP Putting into Operation

1 Putting into Operation

For details refer to the Quick Start Guide chapters 1, "Front and Rear Panel", and 2, "Preparing for Use".

1164.4556.12 1.1 E-2

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Putting into Operation R&S FSP

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R&S FSP Getting Started

2 Getting Started

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2

Measuring the Spectra of Complex Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3

Intermodulation Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3

Measurement Example – Measuring the R&S FSP’s intrinsic intermodulation distance . . . 2.5

Measuring Signals in the Vicinity of Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.10

Measurement example – Measuring the level of the internal reference generator

at low S/N ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.13

Noise Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.16

Measuring noise power density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.17

Measurement example – Measuring the intrinsic noise power density of the

R&S FSP at 1 GHz and calculating the R&S FSP’s noise figure . . . . . . . . . . . . . . . 2.17

Measurement of Noise Power within a Transmission Channel . . . . . . . . . . . . . . . . . . . . . 2.20

Measurement Example – Measuring the intrinsic noise of the R&S FSP at 1

GHz in a 1.23 MHz channel bandwidth with the channel power function . . . . . . . . . 2.20

Measuring Phase Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.25

Measurement Example – Measuring the phase noise of a signal generator at a

carrier offset of 10 kHz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.25

Measurements on Modulated Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.27

Measurements on AM signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.28

Measurement Example 1 – Displaying the AF of an AM signal in the time

domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.28

Measurement Example 2 – Measuring the modulation depth of an AM carrier in

the frequency domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.29

Measurements on FM Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.31

Measurement Example – Displaying the AF of an FM carrier . . . . . . . . . . . . . . . . . 2.31

Measuring Channel Power and Adjacent Channel Power . . . . . . . . . . . . . . . . . . . . . . . . . 2.33

Measurement Example 1 – ACPR measurement on an IS95 CDMA Signal . . . . . . 2.34

Measurement Example 2 – Measuring the adjacent channel power of an IS136

TDMA signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.38

Measurement Example 3 – Measuring the Modulation Spectrum in Burst Mode

with the Gated Sweep Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.41

Measurement Example 4 – Measuring the Transient Spectrum in Burst Mode

with the Fast ACP function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.43

Measurement Example 5 – Measuring adjacent channel power of a W-CDMA

uplink signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.45

Amplitude distribution measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.49

Measurement Example – Measuring the APD and CCDF of white noise

generated by the R&S FSP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.49

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Introduction R&S FSP

Introduction

This chapter explains how to operate the R&S FSP using typical measurements as examples.

The basic operating steps such as selecting the menus and setting parameters are described in the Quick Start Guide, chapter 4, "Basic Operation". Furthermore, the screen structure and displayed function indicators are explained in this chapter.

Chapter “Instrument Functions” describes all the menus and R&S FSP functions.

All of the following examples are based on the standard settings of the Spectrum Analyzer. These are set with the PRESET key. A complete listing of the standard settings can be found in chapter “Instrument

Functions”, section “R&S FSP Initial Configuration – PRESET Key” on page 4.6. Examples of more basic

character are provided in the Quick Start Guide, chapter 5, as an introduction.

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R&S FSP Measuring the Spectra of Complex Signals

Measuring the Spectra of Complex Signals

Intermodulation Measurements

If several signals are applied to a DUT with non-linear characteristics, unwanted mixing products are generated – mostly by active components such as amplifiers or mixers. The products created by 3 intermodulation are particularly troublesome as they have frequencies close to the useful signals and, compared with other products, are closest in level to the useful signals. The fundamental wave of one signal is mixed with the 2

= 2 × fu1 – fu2 (1)

= 2 × fu2 – fu1 (2)

harmonic of the other signal.

order

where f

and fs2 are the frequencies of the intermodulation products and fu1 and fu2 the frequencies of

the useful signals.

The following diagram shows the position of the intermodulation products in the frequency domain.

Level

∆

Frequency

∆

Fig. 2-1 3

order intermodulation products

∆

Example:

fu1 = 100 MHz, fu2 = 100.03 MHz

= 2 × fu1 – fu2 = 2 × 100 MHz – 100.03 MHz = 99.97 MHz

= 2 × fu2 – fu1 = 2 × 100.03 MHz – 100 MHz = 100.06 MHz

The level of the intermodulation products depends on the level of the useful signals. If the level of the two useful signals is increased by 1 dB, the level of the intermodulation products is increased by 3 dB. The intermodulation distance d signals and the 3

order intermodulation products are related.

is, therefore, reduced by 2 dB. Fig. 2-2 shows how the levels of the useful

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Measuring the Spectra of Complex Signals R&S FSP

Output

level

Intercept

point

Compression

Carrier

level

Fig. 2-2 Level of the 3

order intermodulation products as a function of the level of the useful signals

Intermodulation

products

Input level

The behavior of the signals can be explained using an amplifier as an example. The change in the level of the useful signals at the output of the amplifier is proportional to the level change at the input of the amplifier as long as the amplifier is operating in linear range. If the level at the amplifier input is changed by 1 dB, there is a 1 dB level change at the amplifier output. At a certain input level, the amplifier enters saturation. The level at the amplifier output does not increase with increasing input level.

The level of the 3 signals. The 3

order intermodulation products increases 3 times faster than the level of the useful

order intercept is the virtual level at which the level of the useful signals and the level of the spurious products are identical, i.e. the intersection of the two straight lines. This level cannot be measured directly as the amplifier goes into saturation or is damaged before this level is reached.

The 3 d

TOI = a

order intercept can be calculated from the known slopes of the lines, the intermodulation distance

and the level of the useful signals.

/ 2 + Pn (3)

with TOI (Third Order Intercept) being the 3rd order intercept in dBm and P

With an intermodulation distance of 60 dB and an input level, Pw, of –20 dBm, the following 3

the level of a carrier in dBm.

order

intercept is obtained:

TOI = 60 dBm / 2 + (-20 dBm) = 10 dBm.

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R&S FSP Measuring the Spectra of Complex Signals

Measurement Example – Measuring the R&S FSP’s intrinsic intermodulation distance

To measure the intrinsic intermodulation distance, use the following test setup.

Test setup:

Signal

Generator 1

Coupler R&S FSP

Signal

Generator 2

Settings on the signal generator (e.g. R&S SMIQ):

Level Frequency

Signal generator 1 -10 dBm 999.9 MHz

Signal generator 2 -10 dBm 1000.1 MHz

Measurement using the R&S FSP:

1. Set the Spectrum Analyzer to its default settings.

➢ Press the PRESET key.

The R&S FSP is in its default state.

2. Set center frequency to 1 GHz and the frequency span to 1 MHz.

➢ Press the FREQ key and enter 1 GHz. ➢ Press the SPAN key and enter 1 MHz.

3. Set the reference level to –10 dBm and RF attenuation to 0 dB.

➢ Press the AMPT key and enter -10 dBm. ➢ Press the RF ATTEN MANUAL softkey and enter 0 dB.

By reducing the RF attenuation to 0 dB, the level to the R&S FSP input mixer is increased. Therefore, 3

order intermodulation products are displayed.

4. Set the resolution bandwidth to 10 kHz.

➢ Press the BW key. ➢ Press the RES BW MANUAL softkey and enter 10 kHz.

By reducing the bandwidth, the noise is further reduced and the intermodulation products can be clearly seen.

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Measuring the Spectra of Complex Signals R&S FSP

5. Measuring intermodulation by means of the 3

order intercept measurement function

➢ Press the MEAS key. ➢ Press the TOI softkey.

The R&S FSP activates four markers for measuring the intermodulation distance. Two markers are positioned on the useful signals and two on the intermodulation products. The 3

order intercept is calculated from the level difference between the useful signals and the intermodulation products. It is then displayed on the screen:

Fig. 2-3 Result of intrinsic intermodulation measurement on the R&S FSP. The 3

intercept (TOI) is displayed at the top right corner of the grid

The level of a Spectrum Analyzer’s intrinsic intermodulation products depends on the RF level of the useful signals at the input mixer. When the RF attenuation is added, the mixer level is reduced and the intermodulation distance is increased. With an additional RF attenuation of 10 dB, the levels of the intermodulation products are reduced by 20 dB. The noise level is, however, increased by 10 dB.

6. Increasing RF attenuation to 10 dB to reduce intermodulation products.

➢ Press the AMPT key. ➢ Press the RF ATTEN MANUAL softkey and enter 10 dB.

The R&S FSP’s intrinsic intermodulation products disappear below the noise floor.

order

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R&S FSP Measuring the Spectra of Complex Signals

Fig. 2-4 If the RF attenuation is increased, the R&S FSP’s intrinsic intermodulation products

disappear below the noise floor.

Calculation method:

The method used by the R&S FSP to calculate the intercept point takes the average useful signal level P

in dBm and calculates the intermodulation d3 in dB as a function of the average value of the levels of

the two intermodulation products. The third order intercept (TOI) is then calculated as follows:

TOI/dBm = ½ d

+ Pu

Intermodulation- free dynamic range

The Intermodulation – free dynamic range, i.e. the level range in which no internal intermodulation products are generated if two-tone signals are measured, is determined by the 3

order intercept point, the phase noise and the thermal noise of the Spectrum Analyzer. At high signal levels, the range is determined by intermodulation products. At low signal levels, intermodulation products disappear below the noise floor, i.e. the noise floor and the phase noise of the Spectrum Analyzer determine the range. The noise floor and the phase noise depend on the resolution bandwidth that has been selected. At the smallest resolution bandwidth, the noise floor and phase noise are at a minimum and so the maximum range is obtained. However, a large increase in sweep time is required for small resolution bandwidths. It is, therefore, best to select the largest resolution bandwidth possible to obtain the range that is required. Since phase noise decreases as the carrier-offset increases, its influence decreases with increasing frequency offset from the useful signals.

The following diagrams illustrate the intermodulation-free dynamic range as a function of the selected bandwidth and of the level at the input mixer (= signal level – set RF attenuation) at different useful signal offsets.

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Measuring the Spectra of Complex Signals R&S FSP

Distortion free Dynamic Range

-40

-50

-60

-70

-80

-90

-100

-110

-120

-60 -50 -40 -30 -20 -1

RBW = 10

kHz

RBW = 1

kHz

RBW = 100

RBW = 10

(1 MHz carrier offset

Fig. 2-5 Intermodulation-free range of the FSP3 as a function of level at the input mixer and the set

resolution bandwidth (useful signal offset = 1 MHz, DANL = -155 dBm /Hz, TOI = 12 dBm; typ. values at 2 GHz)

)

T.O.I.

Thermal Noise

Mixer level /dBm

The optimum mixer level, i.e. the level at which the intermodulation distance is at its maximum, depends on the bandwidth. At a resolution bandwidth of 10 Hz, it is approx. –42 dBm and at 10 kHz increases to approx. -32 dBm.

Phase noise has a considerable influence on the intermodulation-free range at carrier offsets between 10 and 100 kHz (Fig. 2-6). At greater bandwidths, the influence of the phase noise is greater than it would be with small bandwidths. The optimum mixer level at the bandwidths under consideration becomes almost independent of bandwidth and is approx. –40 dBm.

Distortion free Dynamic Range

-40

-50

-60

-70

-80

-90

-100

-110

-120

RBW = 10

kHz

RBW = 1

kHz

RBW = 100

RBW = 10

-60 -50 -40 -30 -20 -1

(10 to 100 kHz carrier offset

)

Mixer level /dBm

Fig. 2-6 Intermodulation-free dynamic range of the FSP3 as a function of level at the input mixer and

of the selected resolution bandwidth (useful signal offset = 10 to 100 kHz, DANL = -155 dBm /Hz, TOI = 12 dBm; typ. values at 2 GHz).

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R&S FSP Measuring the Spectra of Complex Signals

Hint

If the intermodulation products of a DUT with a very high dynamic range are to be measured and the resolution bandwidth to be used is therefore very small, it is best to measure the levels of the useful signals and those of the intermodulation products separately using a small span. The measurement time will be reduced– in particular if the offset of the useful signals is large. To find signals reliably when frequency span is small, it is best to synchronize the signal sources and the R&S FSP.

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Measuring Signals in the Vicinity of Noise R&S FSP

Measuring Signals in the Vicinity of Noise

The minimum signal level a Spectrum Analyzer can measure is limited by its intrinsic noise. Small signals can be swamped by noise and therefore cannot be measured. For signals that are just above the intrinsic noise, the accuracy of the level measurement is influenced by the intrinsic noise of the Spectrum Analyzer.

The displayed noise level of a Spectrum Analyzer depends on its noise figure, the selected RF attenuation, the selected reference level, the selected resolution and video bandwidth and the detector. The effect of the different parameters is explained in the following.

Impact of the RF attenuation setting

The sensitivity of a Spectrum Analyzer is directly influenced by the selected RF attenuation. The highest sensitivity is obtained at a RF attenuation of 0 dB. The R&S FSP’s RF attenuation can be set in 10 dB steps up to 70 dB (5 dB steps up to 75 dB with option Electronic Attenuator R&S FSP-B25). Each additional 10 dB step reduces the R&S FSP’s sensitivity by 10 dB, i.e. the displayed noise is increased by 10 dB.

Impact of the reference level setting

If the reference level is changed, the R&S FSP changes the gain on the last IF so that the voltage at the logarithmic amplifier and the A/D converter is always the same for signal levels corresponding to the reference level. This ensures that the dynamic range of the log amp or the A/D converter is fully utilized. Therefore, the total gain of the signal path is low at high reference levels and the noise figure of the IF amplifier makes a substantial contribution to the total noise figure of the R&S FSP. The figure below shows the change in the displayed noise depending on the set reference level at 10 kHz and 300 kHz resolution bandwidth. With digital bandwidths (≤100 kHz) the noise increases sharply at high reference levels because of the dynamic range of the A/D converter.

rel. noise level /dB

-2

-70 -60 -50 -40 -30 -20 -10

RBW = 10 kHz

RBW = 300 kH

Reference level /dBm

Fig. 2-7 Change in displayed noise as a function of the selected reference level at bandwidths of

10 kHz and 300 kHz (-30 dBm reference level)

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R&S FSP Measuring Signals in the Vicinity of Noise

Impact of the resolution bandwidth

The sensitivity of a Spectrum Analyzer also directly depends on the selected bandwidth. The highest sensitivity is obtained at the smallest bandwidth (for the R&S FSP: 10 Hz, for FFT filtering: 1 Hz). If the bandwidth is increased, the reduction in sensitivity is proportional to the change in bandwidth. The R&S FSP has bandwidth settings in 3 and 10 sequence. Increasing the bandwidth by a factor of 3 increases the displayed noise by approx. 5 dB (4.77 dB precisely). If the bandwidth is increased by a factor of 10, the displayed noise increases by a factor of 10, i.e. 10 dB. Because of the way the resolution filters are designed, the sensitivity of Spectrum Analyzers often depends on the selected resolution bandwidth. In data sheets, the displayed average noise level is often indicated for the smallest available bandwidth (for the R&S FSP: 10 Hz). The extra sensitivity obtained if the bandwidth is reduced may therefore deviate from the values indicated above. The following table illustrates typical deviations from the noise figure for a resolution bandwidth of 10 kHz which is used as a reference value (= 0 dB).

Noise figure

offset /dB

digital RBW analog RBW

-1 0,01 0,1 1 10 100 1000 10000

RBW /kHz

Fig. 2-8 Change in R&S FSP noise figure at various bandwidths. The reference bandwidth is 10 kHz

Impact of the video bandwidth

The displayed noise of a Spectrum Analyzer is also influenced by the selected video bandwidth. If the video bandwidth is considerably smaller than the resolution bandwidth, noise spikes are suppressed, i.e. the trace becomes much smoother. The level of a sinewave signal is not influenced by the video bandwidth. A sinewave signal can therefore be freed from noise by using a video bandwidth that is small compared with the resolution bandwidth, and thus be measured more accurately.

Impact of the detector

Noise is evaluated differently by the different detectors. The noise display is therefore influenced by the choice of detector. Sinewave signals are weighted in the same way by all detectors, i.e. the level display for a sinewave RF signal does not depend on the selected detector, provided that the signal-to-noise ratio is high enough. The measurement accuracy for signals in the vicinity of intrinsic Spectrum Analyzer noise is also influenced by the detector which has been selected. The R&S FSP has the following detectors:

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Measuring Signals in the Vicinity of Noise R&S FSP

Maximum peak detector

If the max. peak detector s selected, the largest noise display is obtained, since the Spectrum Analyzer displays the highest value of the IF envelope in the frequency range assigned to a pixel at each pixel in the trace. With longer sweep times, the trace indicates higher noise levels since the probability of obtaining a high noise amplitude increases with the dwell time on a pixel. For short sweep times, the display approaches that of the sample detector since the dwell time on a pixel is only sufficient to obtain an instantaneous value.

Minimum peak detector

The min. peak detector indicates the minimum voltage of the IF envelope in the frequency range assigned to a pixel at each pixel in the trace. The noise is strongly suppressed by the minimum peak detector since the lowest noise amplitude that occurs is displayed for each test point. If the signal-to-noise ratio is low, the minimum of the noise overlaying the signal is displayed too low.

At longer sweep times, the trace shows smaller noise levels since the probability of obtaining a low noise amplitude increases with the dwell time on a pixel. For short sweep times, the display approaches that of the sample detector since the dwell time on a pixel is only sufficient to obtain an instantaneous value.

Autopeak detector

The Autopeak detector displays the maximum and minimum peak value at the same time. Both values are measured and their levels are displayed on the screen joint by a vertical line.

Sample detector

The sample detector samples the logarithm of the IF envelope for each pixel of the trace only once and displays the resulting value. If the frequency span of the Spectrum Analyzer is considerably higher than the resolution bandwidth (span/RBW >500), there is no guarantee that useful signals will be detected. They are lost due to undersampling. This does not happen with noise because in this case it is not the instantaneous amplitude that is relevant but only the probability distribution.

RMS detector

For each pixel of the trace, the RMS detector outputs the RMS value of the IF envelope for the frequency range assigned to each test point. It therefore measures noise power. The display for small signals is, however, the sum of signal power and noise power. For short sweep times, i.e. if only one uncorrelated sample value contributes to the RMS value measurement, the RMS detector is equivalent to the sample detector. If the sweep time is longer, more and more uncorrelated RMS values contribute to the RMS value measurement. The trace is, therefore, smoothed. The level of sinewave signals is only displayed correctly if the selected resolution bandwidth (RBW) is at least as wide as the frequency range which corresponds to a pixel in the trace. At a resolution bandwidth of 1 MHz, this means that the maximum frequency display range is 501 MHz.

Average detector

For each pixel of the trace, the average detector outputs the average value of the linear IF envelope for the frequency range assigned to each test point. It therefore measures the linear average noise. The level of sinewave signals is only displayed correctly if the selected resolution bandwidth (RBW) is at least as wide as the frequency range which corresponds to a pixel in the trace. At a resolution bandwidth of 1 MHz, this means the maximum frequency display range is 501 MHz.

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R&S FSP Measuring Signals in the Vicinity of Noise

Quasi peak detector

The quasi peak detector is a peak detector for EMI measurements with defined charge and discharge times. These times are defined in CISPR 16, the standard for equipment used to measure EMI emissions.

Measurement example – Measuring the level of the internal reference generator at low S/N ratios

The example shows the different factors influencing the S/N ratio.

1. Set the Spectrum Analyzer to its default state.

➢ Press the PRESET key.

The R&S FSP is in its default state.

2. Switch on the internal reference generator

➢ Press the SETUP key. ➢ Press the softkeys SERVICE - INPUT CAL.

The internal 128 MHz reference generator is on. The R&S FSP’s RF input is off.

3. Set the center frequency to 128 MHz and the frequency span to 100 MHz.

➢ Press the FREQ key and enter 128 MHz. ➢ Press the SPAN key and enter 100 MHz.

4. Set the RF attenuation to 60 dB to attenuate the input signal or to increase the intrinsic noise.

➢ Press the AMPT key. ➢ Press the RF ATTEN MANUAL softkey and enter 60 dB.

The RF attenuation indicator is marked with an asterisk (*Att 60 dB) to show that it is no longer coupled to the reference level. The high input attenuation reduces the reference signal which can no longer be detected in noise.

Fig. 2-9 Sinewave signal with low S/N ratio. The signal is measured with the autopeak detector

and is completely swamped by the intrinsic noise of the Spectrum Analyzer.

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Measuring Signals in the Vicinity of Noise R&S FSP

5. To suppress noise spikes the trace can be averaged.

➢ Press the TRACE key. ➢ Press the AVERAGE softkey.

The traces of consecutive sweeps are averaged. To perform averaging, the R&S FSP automatically switches on the sample detector. The RF signal, therefore, can be more clearly distinguished from noise.

Fig. 2-10 RF sinewave signal with low S/N ratio if the trace is averaged.

6. Instead of trace averaging, a video filter that is narrower than the resolution bandwidth can be selected.

➢ Press the CLEAR/WRITE softkey in the trace menu. ➢ Press the BW key. ➢ Press the VIDEO BW MANUAL softkey and enter 10 kHz.

The RF signal can be more clearly distinguished from noise.

Fig. 2-11 RF sinewave signal with low S/N ratio if a smaller video bandwidth is selected.

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R&S FSP Measuring Signals in the Vicinity of Noise

7. By reducing the resolution bandwidth by a factor of 10, the noise is reduced by 10 dB.

➢ Press the RES BW MANUAL softkey and enter 300 kHz.

The displayed noise is reduced by approx. 10 dB. The signal, therefore, emerges from noise by about 10 dB. Compared to the previous setting, the video bandwidth has remained the same, i.e. it has increased relative to the smaller resolution bandwidth. The averaging effect is, therefore, reduced by the video bandwidth. The trace will be noisier.

Fig. 2-12 Reference signal at a smaller resolution bandwidth

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Noise Measurements R&S FSP

Noise Measurements

Noise measurements play an important role in spectrum analysis. Noise e.g. affects the sensitivity of radio communication systems and their components.

Noise power is specified either as the total power in the transmission channel or as the power referred to a bandwidth of 1 Hz. The sources of noise are, for example, amplifier noise or noise generated by oscillators used for the frequency conversion of useful signals in receivers or transmitters. The noise at the output of an amplifier is determined by its noise figure and gain.

The noise of an oscillator is determined by phase noise near the oscillator frequency and by thermal noise of the active elements far from the oscillator frequency. Phase noise can mask weak signals near the oscillator frequency and make them impossible to detect.

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R&S FSP Noise Measurements

Measuring noise power density

To measure noise power referred to a bandwidth of 1 Hz at a certain frequency, the R&S FSP has an easyto-use marker function. This marker function calculates the noise power density from the measured marker level.

Measurement example – Measuring the intrinsic noise power density of the R&S FSP at 1 GHz and calculating the R&S FSP’s noise figure

1. Set the Spectrum Analyzer to its default state.

➢ Press the PRESET key.

The R&S FSP is in its default state.

2. Set the center frequency to 1 GHz and the span to 1 MHz.

➢ Press the FREQ key and enter 1 GHz. ➢ Press the SPAN key and enter 1 MHz.

3. Switch on the marker and set the marker frequency to 1 GHz.

➢ Press the MKR key and enter 1 GHz.

4. Switch on the noise marker function.

➢ Press the MEAS key. ➢ Press the NOISE MARKER softkey.

The R&S FSP displays the noise power at 1 GHz in dBm (1Hz).

Since noise is random, a sufficiently long measurement time has to be selected to obtain stable measurement results. This can be achieved by averaging the trace or by selecting a very small video bandwidth relative to the resolution bandwidth.

5. The measurement result is stabilized by averaging the trace

➢ Press the TRACE key. ➢ Press the AVERAGE softkey.

The R&S FSP performs sliding averaging over 10 traces from consecutive sweeps. The measurement result becomes more stable.

Conversion to other reference bandwidths

The result of the noise measurement can be referred to other bandwidths by simple conversion. This is done by adding 10 · log (BW) to the measurement result, BW being the new reference bandwidth.

Example:

A noise power of –150 dBm (1 Hz) is to be referred to a bandwidth of 1 kHz. P

= -150 + 10 · log (1000) = -150 +30 = -120 dBm(1 kHz)

[1kHz]

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Noise Measurements R&S FSP

Calculation method:

The following method is used to calculate the noise power:

If the noise marker is switched on, the R&S FSP automatically activates the sample detector. The video bandwidth is set to 1/10 of the selected resolution bandwidth (RBW).

To calculate the noise, the R&S FSP takes an average over 17 adjacent pixels (the pixel on which the marker is positioned and 8 pixels to the left, 8 pixels to the right of the marker). The measurement result is stabilized by video filtering and averaging over 17 pixels.

Since both video filtering and averaging over 17 trace points is performed in the log display mode, the result would be 2.51 dB too low (difference between logarithmic noise average and noise power). The R&S FSP, therefore, corrects the noise figure by 2.51 dB.

To standardize the measurement result to a bandwidth of 1 Hz, the result is also corrected by –10 · log (RBW

Detector selection

The noise power density is measured in the default setting with the sample detector and using averaging. Other detectors that can be used to perform a measurement giving true results are the average detector or the RMS detector. If the average detector is used, the linear video voltage is averaged and displayed as a pixel. If the RMS detector is used, the squared video voltage is averaged and displayed as a pixel. The averaging time depends on the selected sweep time (=SWT/501). An increase in the sweep time gives a longer averaging time per pixel and thus stabilizes the measurement result. The R&S FSP automatically corrects the measurement result of the noise marker display depending on the selected detector (+1.05 dB for the average detector, 0 dΒ for the RMS detector). It is assumed that the video bandwidth is set to at least three times the resolution bandwidth. While the average or RMS detector is being switched on, the R&S FSP sets the video bandwidth to a suitable value.

), with RBW

noise

being the power bandwidth of the selected resolution filter (RBW).

noise

The Pos Peak, Neg Peak, Auto Peak and Quasi Peak detectors are not suitable for measuring noise power density.

Determining the noise figure:

The noise figure of amplifiers or of the R&S FSP alone can be obtained from the noise power display. Based on the known thermal noise power of a 50 Ω resistor at room temperature (-174 dBm (1Hz)) and the measured noise power P

NF = P

+ 174 – g,

noise

the noise figure (NF) is obtained as follows:

noise

where g = gain of DUT in dB

Example:

The measured internal noise power of the R&S FSP at an attenuation of 0 dB is found to be –153 dBm/1 Hz. The noise figure of the R&S FSP is obtained as follows

NF = -153 + 174 = 19 dB

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R&S FSP Noise Measurements

Co rrectio n factor in dB

Note

If noise power is measured at the output of an amplifier, for example, the sum of the internal noise power and the noise power at the output of the DUT is measured. The noise power of the DUT can be obtained by subtracting the internal noise power from the total power (subtraction of linear noise powers). By means of the following diagram, the noise level of the DUT can be estimated from the level difference between the total and the internal noise level.

-1

-2

-3

-4

-5

-6

-7

-8

-9

-10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Total

ower/intrinsic noise power in dB

Fig. 2-13 Correction factor for measured noise power as a function of the ratio of total power to the

intrinsic noise power of the Spectrum Analyzer.

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Noise Measurements R&S FSP

Measurement of Noise Power within a Transmission Channel

Noise in any bandwidth can be measured with the channel power measurement functions. Thus the noise power in a communication channel can be determined, for example. If the noise spectrum within the channel bandwidth is flat, the noise marker from the previous example can be used to determine the noise power in the channel by considering the channel bandwidth. If, however, phase noise and noise that normally increases towards the carrier is dominant in the channel to be measured, or if there are discrete spurious signals in the channel, the channel power measurement method must be used to obtain correct measurement results.

Measurement Example – Measuring the intrinsic noise of the R&S FSP at 1 GHz in a 1.23 MHz channel bandwidth with the channel power function

Test setup:

The RF input of the R&S FSP remains open-circuited or is terminated with 50 Ω.

Measurement with the R&S FSP:

1. Set the Spectrum Analyzer to its default state.

➢ Press the PRESET key.

The R&S FSP is in its default state.

2. Set the center frequency to 1 GHz and the span to 2 MHz.

➢ Press the FREQ key and enter 1 GHz. ➢ Press the SPAN key and enter 2 MHz.

3. To obtain maximum sensitivity, set RF attenuation on the R&S FSP to 0 dB.

➢ Press the AMPT key. ➢ Press the RF ATTEN MANUAL softkey and enter 0 dB.

4. Switch on and configure the channel power measurement.

➢ Press the MEAS key. ➢ Press the CHAN PWR ACP softkey.

The R&S FSP activates the channel or adjacent channel power measurement according to the currently set configuration.

➢ Press the CP/ACP CONFIG ! softkey.

The R&S FSP enters the submenu for configuring the channel.

➢ Press the CHANNEL BANDWIDTH softkey and enter 1.23 MHz.

The R&S FSP displays the 1.23 MHz channel as two vertical lines which are symmetrical to the center frequency.

➢ Press the PREV key.

The R&S FSP returns to the main menu for channel and adjacent channel power measurement.

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R&S FSP Noise Measurements

➢ Press the ADJUST SETTINGS softkey.

The settings for the frequency span, the bandwidth (RBW and VBW) and the detector are automatically set to the optimum values required for the measurement.

Fig. 2-14 Measurement of the R&S FSP’s intrinsic noise power in a 1.23 MHz channel

bandwidth.

5. Stabilizing the measurement result by increasing the sweep time

➢ Press the SWEEP TIME softkey and enter 1 s.

By increasing the sweep time to 1 s, the trace becomes much smoother thanks to the RMS detector and the channel power measurement display is much more stable.

6. Referring the measured channel power to a bandwidth of 1 Hz

➢ Press the CHAN PWR / Hz softkey.

The channel power is referred to a bandwidth of 1 Hz. The measurement is corrected by -10 · log (ChanBW), with ChanBW being the channel bandwidth that was selected.

Method of calculating the channel power

When measuring the channel power, the R&S FSP integrates the linear power which corresponds to the levels of the pixels within the selected channel. The Spectrum Analyzer uses a resolution bandwidth which is far smaller than the channel bandwidth. When sweeping over the channel, the channel filter is formed by the passband characteristics of the resolution bandwidth (see Fig. 2-15).

-3 dB

Resolution filter

Sweep

Channel bandwith

Fig. 2-15 Approximating the channel filter by sweeping with a small resolution bandwidth

The following steps are performed:

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Noise Measurements R&S FSP

• The linear power of all the trace pixels within the channel is calculated.

P where P L

• The powers of all trace pixels within the channel are summed up and the sum is divided by the number of trace pixels in the channel.

• The result is multiplied by the quotient of the selected channel bandwidth and the noise bandwidth of the resolution filter (RBW).

Since the power calculation is performed by integrating the trace within the channel bandwidth, this method is also called the IBW method (Integration Bandwidth method).

Bandwidth selection (RBW)

For channel power measurements, the resolution bandwidth (RBW) must be small compared to the channel bandwidth, so that the channel bandwidth can be defined precisely. If the resolution bandwidth which has been selected is too wide, this may have a negative effect on the selectivity of the simulated channel filter and result in the power in the adjacent channel being added to the power in the transmit channel. A resolution bandwidth equal to 1% to 3% of the channel bandwidth should, therefore, be selected. If the resolution bandwidth is too small, the required sweep time becomes too long and the measurement time increases considerably.

(Li/10)

= 10

= power of the trace pixel i

= displayed level of trace point i

Detector selection

Since the power of the trace is measured within the channel bandwidth, only the sample detector and RMS detector can be used. These detectors provide measured values that make it possible to calculate the real power. The peak detectors (Pos Peak, Neg Peak and Auto Peak) are not suitable for noise power measurements as no correlation can be established between the peak value of the video voltage and power.

With the sample detector, a value (sample) of the IF envelope voltage is displayed at each trace pixel. Since the frequency spans are very large compared with the resolution bandwidth (span/RBW >501), sinewave signals present in the noise might be lost, i.e. they are not displayed. This is not important for pure noise signals, however, since a single sample in itself is not important - it is the probability distribution of all measured values that counts. The number of samples for power calculation is limited to the number of trace pixels (501 for the R&S FSP).

Note

To increase the repeatability of measurements, averaging is often carried out over several traces (AVERAGE softkey in the TRACE menu). This gives spurious results for channel power measurements (max. –2.51 dB for ideal averaging). Trace averaging should, therefore, be avoided.

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R&S FSP Noise Measurements

With the RMS detector, the whole IF envelope is used to calculate the power for each trace pixel. The IF envelope is digitized using a sampling frequency which is at least five times the resolution bandwidth which has been selected. Based on the sample values, the power is calculated for each trace pixel using the following formula:

RMS

= linear digitized video voltage at the output of the A/D converter

----

N = number of A/D converter values per pixel of the trace P

= power represented by a trace pixel

RMS

When the power has been calculated, the power units are converted into decibels and the value is displayed as a trace pixel.

The number of A/D converter values, N, used to calculate the power, is defined by the sweep time. The time per trace pixel for power measurements is directly proportional to the selected sweep time. The RMS detector uses far more samples for power measurement than the sample detector, especially if the sweep time is increased. The measurement uncertainty can be reduced considerably. In the default setting, the R&S FSP therefore uses the RMS detector to measure the channel power.

For both detectors (sample and RMS), the video bandwidth (VBW) must at least be three times the resolution bandwidth, so that the peak values of the video voltage are not cut off by the video filter. At smaller video bandwidths, the video signal is averaged and the power readout will be too small.

×=

∑

i1=

Sweep time selection

If the sample detector is used, it is best to select the smallest sweep time possible for a given span and resolution bandwidth. The minimum time is obtained if the setting is coupled. This means that the time per measurement is minimal. Extending the measurement time does not have any advantages as the number of samples for calculating the power is defined by the number of trace pixels in the channel.

When using the RMS detector, the repeatability of the measurement results can be influenced by the selection of sweep times. Repeatability is increased at longer sweep times.

Repeatability can be estimated from the following diagram:

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Noise Measurements R&S FSP

max. error/dB

95 % Confidence

0.5

1.5

2.5

level

99 % Confidence

level

100

1000

10000

Number of samples

100000

Fig. 2-16 Repeatability of channel power measurements as a function of the number of samples used

for power calculation

The curves in Fig. 2-16 indicates the repeatability obtained with a probability of 95% and 99% depending on the number of samples used.

The repeatability with 600 samples is ± 0.5 dB. This means that – if the sample detector and a channel bandwidth over the whole diagram (channel bandwidth = span) is used – the measured value lies within ± 0.5 dB of the true value with a probability of 99%.

If the RMS detector is used, the number of samples can be estimated as follows:

Since only uncorrelated samples contribute to the RMS value, the number of samples can be calculated from the sweep time and the resolution bandwidth.

Samples can be assumed to be uncorrelated if sampling is performed at intervals of 1/RBW. The number of uncorrelated samples (N

= SWT × RBW

decorr

The number of uncorrelated samples per trace pixel is obtained by dividing N

) is calculated as follows:

decorr

by 501 (= pixels per

decorr

trace).

Example:

At a resolution bandwidth of 30 kHz and a sweep time of 100 ms, 3000 uncorrelated samples are obtained. If the channel bandwidth is equal to the frequency display range, i.e. all trace pixels are used for the channel power measurement, a repeatability of 0.2 dB with a confidence level of 99% is the estimate that can be derived from Fig. 2-16.

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R&S FSP Noise Measurements

Measuring Phase Noise

The R&S FSP has an easy-to-use marker function for phase noise measurements. This marker function indicates the phase noise of an RF oscillator at any carrier in dBc in a bandwidth of 1 Hz.

Measurement Example – Measuring the phase noise of a signal generator at a carrier offset of 10 kHz

Test setup:

Signal

generator

Settings on the signal generator (e.g. R&S SMIQ):

Frequency: 100 MHz

Level: 0 dBm

FSP

Measurement using R&S FSP:

1. Set the Spectrum Analyzer to its default state

➢ Press the PRESET key.

R&S FSP is in its default state.

2. Set the center frequency to 100 MHz and the span to 50 kHz

➢ Press the FREQ key and enter 100 MHz. ➢ Press the SPAN key and enter 50 kHz.

3. Set the R&S FSP’s reference level to 0 dBm (=signal generator level)

➢ Press the AMPT key and enter 0 dBm.

4. Enable phase noise measurement

➢ Press the MKR FCTN key. ➢ Press the PHASE NOISE ! softkey.

The R&S FSP activates phase noise measurement. Marker 1 (=main marker) and marker 2 (= delta marker) are positioned on the signal maximum. The position of the marker is the reference (level and frequency) for the phase noise measurement. A horizontal line represents the level of the reference point and a vertical line the frequency of the reference point. Data entry for the delta marker is activated so that the frequency offset at which the phase noise is to be measured can be entered directly.

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Noise Measurements R&S FSP

5. 10 kHz frequency offset for determining phase noise.

➢ Enter 10 kHz.

The R&S FSP displays the phase noise at a frequency offset of 10 kHz. The magnitude of the phase noise in dBc/Hz is displayed in the delta marker output field at the top right of the screen (delta 2 [T1 PHN]).

6. Stabilize the measurement result by activating trace averaging.

➢ Press the TRACE key. ➢ Press the AVERAGE softkey.

Fig. 2-17 Measuring phase noise with the phase-noise marker function

The frequency offset can be varied by moving the marker with the spinwheel or by entering a new frequency offset as a number.

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R&S FSP Measurements on Modulated Signals

Measurements on Modulated Signals

If RF signals are used to transmit information, an RF carrier is modulated. Analog modulation methods such as amplitude modulation, frequency modulation and phase modulation have a long history and digital modulation methods are now used for modern systems. Measuring the power and the spectrum of modulated signals is an important task to assure transmission quality and to ensure the integrity of other radio services. This task can be performed easily with a Spectrum Analyzer. Modern Spectrum Analyzers also provide the test routines that are essential to simplify complex measurements.

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Measurements on Modulated Signals R&S FSP

Measurements on AM signals

The Spectrum Analyzer detects the RF input signal and displays the magnitudes of its components as a spectrum. AM modulated signals are also demodulated by this process. The AF voltage can be displayed in the time domain if the modulation sidebands are within the resolution bandwidth. In the frequency domain, the AM sidebands can be resolved with a small bandwidth and can be measured separately. This means that the modulation depth of a carrier modulated with a sinewave signal can be measured. Since the dynamic range of a Spectrum Analyzer is very wide, even extremely small modulation depths can be measured accurately. The R&S FSP has a test routine which measures the modulation depth in %.

Measurement Example 1 – Displaying the AF of an AM signal in the time domain

Test setup:

Signal

generator

Settings on the signal generator (e.g. R&S SMIQ):

Frequency: 100 MHz

Level: 0 dBm

Modulation: 50 % AM, 1 kHz AF

FSP

Measurement with the R&S FSP:

1. Set the Spectrum Analyzer to its default state

➢ Press the PRESET key.

The R&S FSP is in its default state.

2. Set the center frequency to 100 MHz and the span to 0 kHz

➢ Press the FREQ key and enter 100 MHz. ➢ Press the SPAN key and enter 0 Hz.

3. Set the reference level to +6 dBm and the display range to linear

➢ Press the AMPT key and enter 6 dBm. ➢ Press the RANGE LINEAR softkey.

4. Use the video trigger to trigger on the AF signal in order to obtain a stationary display

➢ Press the TRIG key. ➢ Press the VIDEO softkey.

The video trigger level is set to 50% if the instrument is switched on for the first time. The trigger level is displayed as a horizontal line across the graph. The R&S FSP displays the 1 kHz AF signal stably in the time domain.

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R&S FSP Measurements on Modulated Signals

Fig. 2-18 Measuring the AF signal from a 1 kHz AM carrier

If the R&S FSP is equipped with the AM/FM Demodulator option (R&S FSP-B3), the AF can be monitored on the built-in loudspeaker.

5. Switch on the internal AM demodulator

➢ Press the MKR FCTN key. ➢ Press the MKR DEMOD softkey.

The R&S FSP switches the AM demodulator on automatically.

➢ Turn up volume control.

A 1 kHz tone is output by the built-in loudspeaker.

Measurement Example 2 – Measuring the modulation depth of an AM carrier in the frequency domain

Test setup:

Signal

generator

Settings on the signal generator (e.g. R&S SMIQ):

Frequency: 100 MHz

Level: -30 dBm

Modulation: 50 % AM, 1 kHz AF

FSP

Measurement with the R&S FSP:

1. Set the Spectrum Analyzer to its default state

➢ Press the PRESET key.

The R&S FSP is in its default state.

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Measurements on Modulated Signals R&S FSP

2. Set the center frequency to 100 MHz and the span to 0 kHz

➢ Press the FREQ key and enter 100 MHz. ➢ Press the SPAN key and enter 5 kHz.

3. Activate the marker function for AM depth measurement

➢ Press the MEAS key. ➢ Press the MODULATION DEPTH softkey.

The R&S FSP automatically positions a marker on the carrier signal in the middle of the graph and one delta marker on each of the lower and upper AM sidebands. The R&S FSP calculates the AM modulation depth from the ratios of the delta marker levels to the main marker level and outputs the numerical value in the marker info field

Fig. 2-19 Measurement of AM modulation depth. The modulation depth is indicated by

MDEPTH = 49.346 %. The frequency of the AF signal is indicated by the delta markers

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R&S FSP Measurements on Modulated Signals

Measurements on FM Signals

Since Spectrum Analyzers only display the magnitude of signals by means of the envelope detector, the modulation of FM signals cannot be directly measured as is the case with AM signals. With FM signals, the voltage at the output of the envelope detector is constant as long as the frequency deviation of the signal is within the flat part of the passband characteristic of the resolution filter which has been selected. Amplitude variations can only occur if the current frequency lies on the falling edge of the filter characteristic. This effect can be used to demodulate FM signals. The center frequency of the Spectrum Analyzer is set in a way that the nominal frequency of the test signal is on the filter edge (below or above the center frequency). The resolution bandwidth and the frequency offset are selected in a way that the current frequency is on the linear part of the filter slope. The frequency variation of the FM signal is then transformed into an amplitude variation which can be displayed in the time domain.

The R&S FSP's analog 4 linearity, if the frequency of the R&S FSP is set to 1.2 times the filter bandwidth below or above the frequency of the transmit signal. The useful range for FM demodulation is then almost equal to the resolution bandwidth.

Measurement Example – Displaying the AF of an FM carrier

Test setup:

order filters with frequencies from 300 kHz to 3 MHz have a good filter-slope

Signal

generator

Settings on the signal generator (e.g. R&S SMIQ):

Frequency: 100 MHz

Level: -30 dBm

Modulation: FM 0 kHz deviation (i.e., FM = off), 1 kHz AF

FSP

Measurement with the R&S FSP:

1. Set the Spectrum Analyzer to its default state

➢ Press the PRESET key.

The R&S FSP is in its default state.

2. Set the center frequency to 99.64 MHz and the span to 300 kHz.

➢ Press the FREQ key and enter 99.64 MHz. ➢ Press the SPAN key and enter 300 kHz.

3. Set a resolution bandwidth of 300 kHz.

➢ Press the BW key. ➢ Press the RES BW MANUAL softkey and enter 300 kHz.

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Measurements on Modulated Signals R&S FSP

4. Set a display range of 20 dB and shift the filter characteristics to the middle of the display.

➢ Press the AMPT key. ➢ Press the RANGE LOG MANUAL softkey and enter 20 dB. ➢ Press the NEXT key. ➢ Set the GRID softkey to REL. ➢ Press the PREV softkey. ➢ Using the spinwheel, shift the reference level so that the filter edge intersects the - 10 dB level line

at the center frequency.

The slope of the 300 kHz filter is displayed. This corresponds to the demodulator characteristics for FM signals with a slope of approx. 5 dB/100 kHz.

Fig. 2-20 Filter edge of a 300 kHz filter used as an FM-discriminator characteristic

5. Set an FM deviation of 100 kHz and an AF of 1 kHz on the signal generator

6. Set a frequency deviation of 0 Hz on the R&S FSP

➢ Press the SPAN key. ➢ Press the ZERO SPAN.

The demodulated FM signal is displayed. The signal moves across the screen.

7. Creating a stable display by video triggering

➢ Press the TRIG key. ➢ Press the VIDEO softkey.

A stationary display is obtained for the FM AF signal

Result: (-10 ± 5) dB; this means that a deviation of 100 kHz is obtained if the demodulator characteristic slope is 5 dB/100 kHz

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Fig. 2-21 Demodulated FM signal

Measuring Channel Power and Adjacent Channel Power

Measuring channel power and adjacent channel power is one of the most important tasks in the field of digital transmission for a Spectrum Analyzer with the necessary test routines. While, theoretically, channel power could be measured at highest accuracy with a power meter, its low selectivity means that it is not suitable for measuring adjacent channel power as an absolute value or relative to the transmit channel power. The power in the adjacent channels can only be measured with a selective power meter.

A Spectrum Analyzer cannot be classified as a true power meter, because it displays the IF envelope voltage. However, it is calibrated such as to correctly display the power of a pure sinewave signal irrespective of the selected detector. This calibration is not valid for non-sinusoidal signals. Assuming that the digitally modulated signal has a Gaussian amplitude distribution, the signal power within the selected resolution bandwidth can be obtained using correction factors. These correction factors are normally used by the Spectrum Analyzer's internal power measurement routines in order to determine the signal power from IF envelope measurements. These factors are valid if and only if the assumption of a Gaussian amplitude distribution is correct.

Apart from this common method, the R&S FSP also has a true power detector, i.e. an RMS detector. It correctly displays the power of the test signal within the selected resolution bandwidth irrespective of the amplitude distribution, without additional correction factors being required. With an absolute measurement uncertainty of < 0.5 dB and a relative measurement uncertainty of < 0.2 dB (each with a confidence level of 95%), the R&S FSP comes close to being a true power meter.

There are two possible methods for measuring channel and adjacent channel power with a Spectrum Analyzer:

The IBW method (Integration Bandwidth Method) in which the Spectrum Analyzer measures with a resolution bandwidth that is less than the channel bandwidth and integrates the level values of the trace versus the channel bandwidth. This method is described in the section on noise measurements.

Measurement using a channel filter.

In this case, the Spectrum Analyzer makes measurements in the time domain using an IF filter that corresponds to the channel bandwidth. The power is measured at the output of the IF filter. Until now, this method has not been used for Spectrum Analyzers, because channel filters were not available and the resolution bandwidths, optimized for the sweep, did not have a sufficient selectivity. The method was reserved for special receivers optimized for a particular transmission method.

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The R&S FSP has test routines for simple channel and adjacent channel power measurements. These routines give quick results without any complex or tedious setting procedures.

Measurement Example 1 – ACPR measurement on an IS95 CDMA Signal

Test setup:

Signal

generator

Settings on the signal generator (e.g. R&S SMIQ):

Frequency: 850 MHz

Level: 0 dBm

Modulation: CDMA IS 95

FSP

Measurement with the R&S FSP:

1. Set the Spectrum Analyzer to its default state.

➢ Press the PRESET key.

The R&S FSP is in its default state.

2. Set the center frequency to 850 MHz and frequency deviation to 4 MHz.

➢ Press the FREQ key and enter 850 MHz.

3. Set the reference level to +10 dBm.

➢ Press the AMPT key and enter 10 dBm.

4. Configuring the adjacent channel power for the CDMA IS95 reverse link.

➢ Press the MEAS key. ➢ Press the CHAN PWR ACP ! softkey. ➢ Press the CP/ACP STANDARD softkey.

From the list of standards, select CDMA IS95A REV using the spinwheel or the cursor down key below the spinwheel and press ENTER.

The R&S FSP sets the channel configuration according to the IS95 standard for mobile stations with 2 adjacent channels above and below the transmit channel. The spectrum is displayed in the upper part of the screen, the numeric values of the results and the channel configuration in the lower part of the screen. The various channels are represented by vertical lines on the graph. The frequency span, resolution bandwidth, video bandwidth and detector are selected automatically to give correct results. To obtain stable results - especially in the adjacent channels (30 kHz bandwidth) which are narrow in comparison with the transmission channel bandwidth (1.23 MHz) - the RMS detector is used.

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5. Set the optimal reference level and RF attenuation for the applied signal level.

➢ Press the ADJUST REF LVL softkey.

The R&S FSP sets the optimal RF attenuation and the reference level based on the transmission channel power to obtain the maximum dynamic range. The following figure shows the result of the measurement.

Fig. 2-22 Adjacent channel power measurement on a CDMA IS95 signal

The repeatability of the results, especially in the narrow adjacent channels, strongly depends on the measurement time since the dwell time within the 30 kHz channels is only a fraction of the complete sweep time. A longer sweep time may increase the probability that the measured value converges to the true value of the adjacent channel power, but this increases measurement time.

To avoid long measurement times, the R&S FSP measures the adjacent channel power in the time domain (FAST ACP). In the FAST ACP mode, the R&S FSP measures the power of each channel at the defined channel bandwidth, while being tuned to the center frequency of the channel in question. The digital implementation of the resolution bandwidths makes it possible to select a filter characteristics that is precisely tailored to the signal. In case of CDMA IS95, the power in the useful channel is measured with a bandwidth of 1.23 MHz and that of the adjacent channels with a bandwidth of 30 kHz. Therefore the R&S FSP jumps from one channel to the other and measures the power at a bandwidth of 1.23 MHz or 30 kHz using the RMS detector. The measurement time per channel is set with the sweep time. It is equal to the selected measurement time divided by the selected number of channels. The five channels from the above example and the sweep time of 100 ms give a measurement time per channel of 20 ms.

Compared to the measurement time per channel given by the span (= 5 MHz) and sweep time (= 100 ms, equal to 1.66 ms per 30 kHz channel) used in the example, this is a far longer dwell time on the adjacent channels (factor of 12). In terms of the number of uncorrelated samples this means 20000/33 µs = 606 samples per channel measurement compared to 1667/33µs = 50.5 samples per channel measurement.

Repeatability with a confidence level of 95% is increased from ± 1.4 dB to ± 0.38 dB as shown in

Fig. 2-16. For the same repeatability, the sweep time would have to be set to 1.2 s with the

integration method. The following figure shows the standard deviation of the results as a function of the sweep time.

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ACPR Repeatability IS95

IBW Method

1,4

1,2

0,8

0,6

Standard dev / dB

0,4

0,2

10 100 1000

Alternate channels

Fig. 2-23 Repeatability of adjacent channel power measurement on IS95-standard signals if the

integration bandwidth method is used

6. Switch to Fast ACP to increase the repeatability of results.

➢ Press the CP/ACP CONFIG ! softkey. ➢ Set the FAST ACP softkey to ON. ➢ Press the ADJUST REF LVL softkey.

The R&S FSP measures the power of each channel in the time domain. The trace represents power as a function of time for each channel (see Fig. 2-24). The numerical results over consecutive measurements become much more stable.

Adjacent channels

Tx cha nnel

Sweep time/ms

Fig. 2-24 Measuring the channel power and adjacent channel power ratio for IS95 signals in the

time domain (Fast ACP)

The following figure shows the repeatability of power measurements in the transmit channel and of relative power measurements in the adjacent channels as a function of sweep time. The standard deviation of measurement results is calculated from 100 consecutive measurements as shown in

Fig. 2-23. Take scaling into account if comparing power values.

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ACPR IS95 Repeatability

0,35

0,3

0,25

0,2

0,15

Standard dev /dB

0,1

0,05

10 100 1000

Tx channel

Alternate channels

Fig. 2-25 Repeatability of adjacent channel power measurements on IS95 signals in the Fast

ACP mode

Adjacent channels

Sweep time/ms

Note on adjacent channel power measurements on IS95 base-station signals:

When measuring the adjacent channel power of IS95 base-station signals, the frequency spacing of the adjacent channel to the nominal transmit channel is specified as ±750 kHz. The adjacent channels are, therefore, so close to the transmit channel that the power of the transmit signal leaks across and is also measured in the adjacent channel if the usual method using the 30 kHz resolution bandwidth is applied. The reason is the low selectivity of the 30 kHz resolution filter. The resolution bandwidth, therefore, must be reduced considerably, e.g. to 3 kHz to avoid this. This causes very long measurement times (factor of 100 between a 30 kHz and 3 kHz resolution bandwidth).

This effect is avoided with the time domain method which uses steep IF filters. The 30 kHz channel filter implemented in the R&S FSP has a very high selectivity so that even with a ±750 kHz spacing to the transmit channel the power of the useful modulation spectrum is not measured.

The following figure shows the passband characteristics of the 30 kHz channel filter in the R&S FSP.

Fig. 2-26 Frequency response of the 30 kHz channel filter for measuring the power in the IS 95

adjacent channel

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Measurement Example 2 – Measuring the adjacent channel power of an IS136 TDMA signal

Test setup:

Signal

generator

Ext Ref Out

Settings on the signal generator (e.g. R&S SMIQ):

Frequency: 850 MHz

Level: -20 dBm

Modulation: IS136/NADC

RF Inp

Note

As the modulation spectrum of the IS136 signal leaks into the adjacent channel, it makes a contribution to the power in the adjacent channel. Exact tuning of the Spectrum Analyzer to the transmit frequency is therefore critical. If tuning is not precise, the adjacent channel power ratios in the lower and upper adjacent channels become asymmetrical. The R&S FSP’s frequency and the generator frequency are therefore synchronized.

FSP

Ext Ref IN

Measurement with the R&S FSP

1. Set the Spectrum Analyzer to its default state.

➢ Press the PRESET key.

The R&S FSP is in its default state.

2. Set up the R&S FSP for synchronization to an external reference frequency.

➢ Press the SETUP key. ➢ Set the REFERENCE softkey to EXT.

3. Set the center frequency to 850 MHz-

Press the FREQ key and enter 850 MHz.

4. Configure adjacent channel power measurement for IS136 signals.

➢ Press the MEAS key. ➢ Press the CHAN PWR ACP ! softkey. ➢ Press the CP/ACP STANDARD softkey.

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➢ Select NADC IS136 from the list of standards and press ENTER.

The R&S FSP performs the power measurement in 5 channels (in the useful channel and in the two upper and two lower adjacent channels).

5. Setting the optimum reference level and RF attenuation for the measurement

➢ Press the ADJUST REF LEVEL softkey.

The R&S FSP sets the optimum RF attenuation and the optimum reference level on the basis of the measured channel power.

Fig. 2-27 Measuring the relative adjacent channel power of an NADC signal in each of the two

adjacent channels below and above the transmit channel.

To increase repeatability – especially in the adjacent channels – the R&S FSP’s Fast ACP routine is recommended.

6. Switching on the Fast ACP routine.

➢ Press the CP/ACP CONFIG ! softkey ➢ Set the FAST ACP softkey to ON.

➢ Press the ADJUST REF LEVEL softkey.

The R&S FSP makes consecutive measurements on the 5 channels in the Zero Span mode using the receive filter specified in IS 136 to define the resolution bandwidth. The power in each channel is displayed on the graph as a function of time

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Fig. 2-28 Measuring adjacent channel power in time domain (Fast ACP)

As the resolution bandwidth is much wider than the one used for the integration method, the results are much more stable when compared at the same sweep time.

Repeatability can be influenced by the selected sweep time. The results become much more stable if long sweep times are selected. Since the amplitude distribution is different in different channels (part of the modulation spectrum falls within the first adjacent channel), the repeatability depends on the spacing of the measured channel from the transmit channel.

Fig. 2-29 below shows the standard deviation of results in the different channels as a function of

the selected sweep time. The standard deviation for the various sweep times was recorded using a signal generator as a source. With real DUTs the amplitude distributions in adjacent channels may be different so that the standard deviation could differ from that shown in Fig. 2-29. To evaluate the correct measuring time for time-critical measurements at a given standard deviation, the standard deviation of the ACP values at the output of the real DUT must be determined.

NADC Rep eatability

1.4

1.2

0.8

0.6

0.4

Standard Deviation / dB

0.2

10 100 1000

Alt1 Channels

Tx Channel

Adj Channels

Swe ep Ti me / ms

Fig. 2-29 Standard deviation of the results of Fast ACP measurement as a function of selected

sweep time evaluated from 100 measurements per sweep time

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Measurement Example 3 – Measuring the Modulation Spectrum in Burst Mode with the Gated Sweep Function

Since transmission systems compliant to IS136 use a TDMA method, the adjacent channel power must also be measured in burst mode. An IS136 TDMA frame is divided into 6 time slots. Two of these slots are assigned to a subscriber. This means that the ratio of transmit time to off-time for IS136 mobile phones is only 1:3 (e.g. time slots 1 and 4)

The R&S FSP supports the measurement of the adjacent channel power in the TDMA mode with the Gated Sweep function.

Test setup with the R&S Signal Generator SMIQ:

SMIQ-Z5

Par Data Output

Signal

generator

SMIQ

The R&S SMIQ has to be equipped with options R&S SMIQ-B10 or R&S SMIQ-B20 (modulation coder) and R&S SMIQ-B11 (data generator).

Option R&S SMIQ-Z5 is required to trigger the R&S FSP. This option is connected to the R&S SMIQ’s parallel output port. The BNC output Trigger 1 of the R&S SMIQ-Z5 provides a TTL trigger signal on the rising edge of the IS136 burst, which is used to start the R&S FSP sweep in the Gated Sweep mode.

Trigger1

Ext Gate/Trig IN

RF Inp

Note

The R&S FSP’s IF power trigger is not suitable for IS136. It triggers on every level edge of the input signal. Since the modulation of the IS136 signal causes level dips even during the transmit burst, there is no way of ensuring that the R&S FSP is only triggered on the burst edge.

FSP

Ext Ref INExt Ref Out

Settings on signal generator R&S SMIQ:

Switch the signal generator to the IS136 burst mode (time slots 1 and 4 are switched on, the other time slots are switched off).

The R&S SMIQ is set as follows to generate the signal:

➢ Press the PRESET key. ➢ Press the FREQ key and enter 850 MHz. ➢ Press the LEVEL key and enter -20 dBm. ➢ Press the RETURN key. ➢ Select DIGITAL STANDARD using the spinwheel and press the SELECT key. ➢ Select NADC using the spinwheel and press the SELECT key.

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➢ Press the SELECT key. ➢ Select ON using the spinwheel and press the SELECT key. ➢ Press the RETURN key. ➢ Keep turning the spinwheel until SAVE/RECALL FRAME appears in the list and select the menu item

SAVE/RECALL FRAME using the SELECT key.

➢ The cursor is set to GET PREDEFINED FRAME. ➢ Press the SELECT key. ➢ Select UP1TCH using the spinwheel and press the SELECT key.

In the following operating sequence for the R&S FSP, it is assumed that steps 1 to 6 of the previous example (“Measurement Example 2 – Measuring the adjacent channel power of an IS136 TDMA signal”) have already been performed.

1. Configuring the Gated Sweep function on the R&S FSP.

➢ Press the TRIG key. ➢ Press the GATED TRIGGER softkey. ➢ Press the EXTERN softkey. ➢ Press the GATE SETTINGS ! softkey.

The R&S FSP switches to time domain measurement so that the setting of the Gated Sweep parameters can be checked visually.

➢ Press the SWEEPTIME softkey and enter 10 ms.

Exactly one TDMA burst will be displayed.

➢ Press the GATE DELAY softkey and enter 2 ms or set the Gate Delay using the spinwheel so that

the burst is reliably detected.

➢ Press the GATE LENGTH softkey and enter 5 ms or set the vertical line for the gate length using

the spinwheel so that the burst is reliably detected.

Fig. 2-30 Setting the parameters Gate Delay and Gate Length in time domain. The time interval

required to measure the spectrum is indicated by two vertical lines.

➢ Press the PREV key.

The R&S FSP now performs the ACP measurement only during the switch-on phase of the TDMA burst. The measurement is stopped during the switch-off phase.

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Note

The selected sweep time is the net sweep time, i.e. the time during which the R&S FSP is actually measuring. The complete frame of an IS136 signal takes 40 ms. In the above example, measurement only takes place for 2x5 ms within a frame. The R&S FSP is therefore only measuring for 25% of the frame duration. The total measuring time is therefore four times that for the CW mode.

Measurement Example 4 – Measuring the Transient Spectrum in Burst Mode with the Fast ACP function

In addition to the modulation spectrum or adjacent channel power from the modulation of the RF carrier, the spectrum or adjacent channel power generated by burst edges is also to be measured in TDMA systems. The spectrum is a pulse spectrum and must be measured with the peak detector. With the usual IBW method, only the power of the continuously modulated signal can be measured properly. Even if the modulation spectrum is transmitted in the TDMA mode, the measurement of the modulation spectrum will work because the burst edges are blanked out for the measurement by means of the Gated Sweep function. The Spectrum Analyzer performs measurements only if the modulation spectrum is continuous when the burst is on.

However, the IBW method fails for the spectrum created by the burst edges. As the measurement is carried out with resolution bandwidths that are very small compared to the signal bandwidth, a spurious amplitude distribution is obtained in the defined measurement channel because of the resolution bandwidth. The small resolution bandwidth cannot settle to the peak amplitudes of the test signal. This problem is avoided in the R&S FSP by performing time domain measurements with the root raised cosine filter specified in the IS136 standard.

If the peak detector is used instead of the default RMS detector (which is selected when the standard is selected), the true adjacent channel power generated by the burst edges can also be measured.

Test setup:

The test setup for this example and the settings for R&S SMIQ are identical to those in the previous example.

Measurement with the R&S FSP:

1. Set the Spectrum Analyzer to its default state.

➢ Press the PRESET key.

The R&S FSP is in its default state.

2. Synchronize the R&S FSP to an external reference frequency.

➢ Press the SETUP key. ➢ Set the REFERENCE softkey to EXT.

3. Set the center frequency to 850 MHz

➢ Press the FREQ key and enter 850 MHz.

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4. Configure the adjacent channel power measurement for IS136 signals in Fast ACP mode.

➢ Press the MEAS key. ➢ Press the CHAN PWR ACP ! softkey. ➢ Press the CP/ACP STANDARD softkey. ➢ Select NADC IS136 from the list of standards and press ENTER. ➢ Press the CP/ACP CONFIG ! softkey. ➢ Set the FAST ACP softkey to ON.

The R&S FSP performs the power measurement in 5 channels (in the useful channel and in the two upper and lower adjacent channels).

5. Set the optimum reference level and RF attenuation for the measurement.

➢ Press the ADJUST REF LEVEL softkey.

The R&S FSP sets the optimum RF attenuation and the optimum reference level on the basis of the measured channel power.

6. Select the peak detector and increase the sweep time to 10 s.

➢ Press the TRACE key. ➢ Press the DETECTOR softkey. ➢ Press the DETECTOR MAX PEAK softkey. ➢ Press the SWEEP key. ➢ Press the SWEEP TIME softkey and enter 10 s.

The R&S FSP measures the adjacent channel power generated by the burst edges and the modulation.

Fig. 2-31 Adjacent channel power due to modulation spectrum and transient spectrum

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R&S FSP Measurements on Modulated Signals

Note

The peak power display depends on the selected sweep time. The longer the sweep time, the higher the probability of measuring the highest peak amplitude of the signal. With shorter sweep times, level dips can be seen in the time domain traces. These level dips come from the burst characteristics of the signal. The numerical results, however, indicate the peak amplitudes during the measurement in the corresponding channel.

Measurement Example 5 – Measuring adjacent channel power of a WCDMA uplink signal

Test setup:

Signal

generator

FSP

Settings on the signal generator (e.g. R&S SMIQ):

Frequency: 1950 MHz

Level: 4 dBm

Modulation: 3 GPP W-CDMA Reverse Link

Measurement with the R&S FSP:

1. Set the Spectrum Analyzer to its default state.

➢ Press the PRESET key.

The R&S FSP is in its default state.

2. Set the center frequency to 1950 MHz.

➢ Press the FREQ key and enter 1950 MHz.

3. Switch on the ACP measurement for W-CDMA.

➢ Press the MEAS key. ➢ Press the CHAN PWR ACP ! softkey. ➢ Press the CP/ACP STANDARD softkey.

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➢ From the list of standards, select W-CDMA 3GPP REV using the spinwheel or the cursor down key

below the spinwheel and press ENTER. The R&S FSP sets the channel configuration to the 3GPP W-CDMA standard for mobiles with two adjacent channels above and below the transmit channel. The frequency span, the resolution and video bandwidth and the detector are automatically set to the correct values. The spectrum is displayed in the upper part of the screen and the channel power, the level ratios of the adjacent channel powers and the channel configuration in the lower part of the screen. The individual channels are displayed as vertical lines on the graph.

4. Set the optimum reference level and the RF attenuation for the applied signal level.

➢ Press the ADJUST REF LEVEL softkey.

The R&S FSP sets the optimum RF attenuation and the reference level for the power in the transmission channel to obtain the maximum dynamic range. The following figure shows the result of the measurement:

Fig. 2-32 Measuring the relative adjacent channel power on a W-CDMA uplink signal

5. Measuring adjacent channel power with the Fast ACP method.

➢ Press the CP/ACP CONFIG ! softkey. ➢ Set FAST ACP softkey to ON. ➢ Press the ADJUST REF LVL softkey.

The R&S FSP measures the power of the individual channels in the time domain. A root raised cosine filter with the parameters α = 0.22 and chip rate 3.84 Mcps (= receive filter for 3GPP WCDMA) is used as the channel filter.

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Fig. 2-33 Measuring the adjacent channel power of a W-CDMA signal with the Fast ACP

method

Optimum Level Setting for ACP Measurements on W-CDMA Signals

The dynamic range for ACPR measurements is limited by the thermal noise floor, the phase noise and the intermodulation (spectral regrowth) of the Spectrum Analyzer. The power values produced by the R&S FSP due to these factors accumulate linearly. They depend on the applied level at the input mixer. The three factors are shown in the figure below for the adjacent channel (5 MHz carrier offset)

Note

With W-CDMA, the R&S FSP’s dynamic range for adjacent channel measurements is limited by the 12-bit A/D converter. The greatest dynamic range is, therefore, obtained with the IBW method.

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ACLR / dBc

-30

-35

-40

-45

-50

-55

-60

-65

-70

-75

-80

-40-35-30-25-20-15-10

Phase Noise

Thermal Noise

optimum 10-dB range

Fig. 2-34 The R&S FSP’s dynamic range for adjacent channel power measurements on W-CDMA

uplink signals is a function of the mixer level.

The level of the W-CDMA signal at the input mixer is shown on the horizontal axis, i.e. the measured signal level minus the selected RF attenuation. The individual components which contribute to the power in the adjacent channel and the resulting relative level (total ACPR) in the adjacent channel are displayed on the vertical axis. The optimum mixer level is –21 dBm. The relative adjacent channel power (ACPR) at an optimum mixer level is –65 dBc. Since, at a given signal level, the mixer level is set in 10 dB steps with the 10 dB RF attenuator, the optimum 10 dB range is shown in the figure: it spreads from -16 dBm to -26 dBm. The obtainable dynamic range in this range is 62 dB.

Total ACLR

S.R.I.

Mixer Level / dBm

To set the attenuation parameter manually, the following method is recommended:

• Set the RF attenuation so that the mixer level (= measured channel power – RF attenuation) is between -16 dBm and -26 dBm.

• Set the reference level to the largest possible value where no overload (IFOVLD) is indicated.

This method is automated with the R&S FSP’s ADJUST REF LEVEL function. Especially in remote control mode, e.g. in production environments, it is best to correctly set the attenuation parameters prior to the measurement, as the time required for automatic setting can be saved.

1164.4556.12 2.48 E-2

Note

To measure the R&S FSP’s intrinsic dynamic range for W-CDMA adjacent channel power measurements, a filter which suppresses the adjacent channel power is required at the output of the transmitter. A SAW filter with a bandwidth of 4 MHz, for example, can be used.

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R&S FSP Measurements on Modulated Signals

Amplitude distribution measurements

If modulation types that do not have a constant envelope in the time domain are used, the transmitter has to handle peak amplitudes that are greater than the average power. This includes all modulation types that involve amplitude modulation, QPSK for example. CDMA transmission modes in particular may have power peaks that are large compared to the average power.

For signals of this kind, the transmitter must provide large reserves for the peak power to prevent signal compression and thus an increase of the bit error rate at the receiver.

The peak power, or the crest factor of a signal is therefore an important transmitter design criterion. The crest factor is defined as the peak power / mean power ratio or, logarithmically, as the peak level minus the average level of the signal.

To reduce power consumption and cut costs, transmitters are not designed for the largest power that could ever occur, but for a power that has a specified probability of being exceeded (e.g. 0.01%).

To measure the amplitude distribution, the R&S FSP has simple measurement functions to determine both the APD = Amplitude Probability Distribution and CCDF = Complementary Cumulative Distribution Function.

In the APD display mode, the probability of occurrence of a certain level is plotted against the level.

In the CCDF display mode, the probability that the mean signal power will be exceeded is shown in percent.

Note

In the literature, APD is also used for the probability of amplitude violation. This is the complimentary function to the APD function of R&S FSP. The term PDF (=Probability Density Function) which is frequently used in the literature corresponds to the APD function of R&S FSP.

Measurement Example – Measuring the APD and CCDF of white noise generated by the R&S FSP

1. Set the Spectrum Analyzer to its default state.

➢ Press the PRESET key.

The R&S FSP is in its default state.

2. Configure the R&S FSP for APD measurement

➢ Press the AMPT key and enter -60 dBm.

The R&S FSP’s intrinsic noise is displayed at the top of the screen.

➢ Press the MEAS key. ➢ Press the SIGNAL STATISTIC ! softkey. ➢ Set the APD softkey to ON.

The R&S FSP sets the frequency span to 0 Hz and measures the amplitude probability distribution (APD). The number of uncorrelated level measurements used for the measurement is 100000. The mean power and the peak power are displayed in dBm. The crest factor (peak power – mean power) is output as well (see Fig. 2-35).

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Fig. 2-35 Amplitude probability distribution of white noise

3. Switch to the CCDF display mode.

➢ Set the CCDF softkey to ON

The APD measurement is switched off and the CCDF display mode is switched on.

Fig. 2-36 The CCDF of white noise

The CCDF trace indicates the probability that a level will exceed the mean power. The level above the mean power is plotted along the X axis of the graph.The origin of the axis corresponds to the mean power level. The probability that a level will be exceeded is plotted along the Y axis.

4. Bandwidth selection

If the amplitude distribution is measured, the resolution bandwidth must be set in a way that the complete spectrum of the signal to be measured falls within the bandwidth. This is the only way of ensuring that all the amplitudes will pass through the IF filter without being distorted. If the selected resolution bandwidth is too small for a digitally modulated signal, the amplitude distribution at the output of the IF filter becomes a Gaussian distribution according to the central limit theorem and so corresponds to a white noise signal. The true amplitude distribution of the signal therefore cannot be determined.

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A video bandwidth which is large in comparison to the resolution bandwidth (≥ 3 x RBW) must be selected. This ensures that the amplitude peaks of the signal are not smoothed by the lowpass effect of the video filter. The video bandwidth is set automatically during statistics measurements.

Since the video bandwidth of the R&S FSP is limited to 10 MHz, lowpass filtering occurs during measurements with a resolution bandwidth of 10 MHz. Additional band-limiting occurs at a resolution bandwidth of 10 MHz due to the lowpass filtering at the output of the log amplifier. The latter limits the video signal to a bandwidth of 8 MHz in order to obtain sufficient suppression of the 20.4 MHz IF. The level range of the signal amplitudes, e.g. during APD white-noise measurements, is smaller. For broadband-modulated signals such as W-CDMA signals, the effect depends on the bandwidth occupied by the signal. At a signal bandwidth of 4 MHz, the amplitude distribution can be measured correctly with the effective video bandwidth.

5. Selecting the number of samples

For statistics measurements with the R&S FSP, the number of samples N

Samples

is entered for statistical evaluation instead of the sweep time. Since only statistically independent samples contribute to statistics, the measurement or sweep time is calculated automatically. It is indicated on the R&S FSP display. The samples are statistically independent if the time difference is at least 1/RBW. The sweep time SWT is, therefore, expressed as follows:

SWT = N

Samples

/RBW

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Measurements on Modulated Signals R&S FSP

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Page 63

R&S FSP Manual Control

3 Manual Control

For details refer to the Quick Start Guide, chapter 4, "Basic Operation".

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Manual Control R&S FSP

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R&S FSP Instrument Functions

4 Instrument Functions

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5

R&S FSP Initial Configuration – PRESET Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6

Mode Selection – Hotkey Bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8

Return to Manual Control – LOCAL Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9

Analyzer Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10

Frequency and Span Selection – FREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11

Setting the Frequency Span – SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.15

Level Display Setting and RF Input Configuration – AMPT . . . . . . . . . . . . . . . . . . . . . . . . 4.17

Electronic Attenuator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.21

Setting the Bandwidths and Sweep Time – BW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.23

Filter Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.29

List of Available Channel Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.30

Sweep Settings – SWEEP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.33

Triggering the Sweep – TRIG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.36

Option R&S FSP-B6 – TV and RF Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.43

Selection and Setting of Traces – TRACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.47

Selection of Trace Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.47

Selection of Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.55

Mathematical Functions for Traces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.60

Recording the Correction Data – CAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.62

Markers and Delta Markers – MKR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.65

Frequency Measurement with the Frequency Counter . . . . . . . . . . . . . . . . . . . . . . 4.68

Marker Functions – MKR FCTN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.73

Activating the Markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.73

Measurement of Noise Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.74

Phase Noise Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.75

Measurement of the Filter or Signal Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.78

Measurement of a Peak List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.79

AF Demodulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.81

Selecting the Trace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.82

Change of Settings via Markers – MKR-> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.84

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Instrument Functions R&S FSP

Power Measurements – MEAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.92

Power Measurement in Time Domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.93

Channel and Adjacent-Channel Power Measurements . . . . . . . . . . . . . . . . . . . . . . 4.99

Setting the Channel Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.108

Measurement of Signal Amplitude Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.122

Measurement of Carrier/Noise Ratio C/N and C/N

Measurement of the AM Modulation Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.131

Measurement of the Third Order Intercept (TOI) . . . . . . . . . . . . . . . . . . . . . . . . . . 4.132

Harmonic Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.135

Measuring Spurious Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.137

Basic Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.145

Setup of Limit Lines and Display Lines – LINES Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.145

Selection of Limit Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.146

Entry and Editing of Limit Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.149

Display Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.154

Configuration of Screen Display – DISP Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.158

Instrument Setup and Interface Configuration – SETUP Key . . . . . . . . . . . . . . . . . . . . . . 4.164

External Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.165

External Noise Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.166

RF Preamplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.166

Transducer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.166

Programming the Interface Configuration and Time Setup . . . . . . . . . . . . . . . . . . 4.172

System Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.182

Service Menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.185

Firmware Update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.188

. . . . . . . . . . . . . . . . . . . . . . . . 4.128

Saving and Recalling Data Sets – FILE Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.190

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.190

Storing a Device Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.191

Loading a Data Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.192

Automatic Loading of a Data Set during Booting . . . . . . . . . . . . . . . . . . . . . . . . . . 4.193

Copying Data Sets to Disk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.194

Description of the Individual Softkeys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.194

Operating Concept of File Managers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.200

Measurement Documentation – HCOPY Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.207

Selecting Printer, Clipboard and File Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.210

File Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.211

Clipboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.211

Printer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.211

Selecting Alternative Printer Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.213

Selecting Printer Colors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.213

Tracking Generator – Option R&S FSP-B9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.216

Tracking Generator Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.217

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R&S FSP Instrument Functions

Transmission Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.220

Calibration of Transmission Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.220

Normalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.221

Reflection Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.226

Calibration of Reflection Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.226

Calibration Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.228

Frequency-Converting Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.230

External Modulation of the Tracking Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.231

Power Offset of the Tracking Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.234

External Generator Control – Option R&S FSP-B10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.235

External Generator Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.237

Transmission Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.239

Calibration of Transmission Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.239

Normalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.241

Reflection Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.245

Calibration of Reflection Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.245

Calibration Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.246

Frequency-Converting Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.248

Configuration of an External Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.249

List of Generator Types Supported by the R&S FSP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.253

LAN Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.258

NOVELL Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.258

MICROSOFT Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.258

Remote Data Transfer with TCP/IP Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.259

RSIB Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.261

Remote Control via RSIB Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.262

Windows Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.262

UNIX Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.262

RSIB Interface Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.264

Overview of Interface Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.264

Variables ibsta, iberr, ibcntl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.264

Description of Interface Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.265

Programming via the RSIB Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.273

Visual Basic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.273

Visual Basic for Applications (Winword and Excel) . . . . . . . . . . . . . . . . . . . . . . . . 4.276

C / C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.277

LO/IF ports for external mixers - Option R&S FSP-B21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.280

Connecting an External Mixer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.280

Manual Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.282

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Instrument Functions R&S FSP

Conversion Loss Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.288

Editing a Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.291

Signal Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.295

Remarks Concerning Signal Identification with AUTO ID . . . . . . . . . . . . . . . . . . . . 4.296

Introductory Example of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.302

Trigger Port – Option R&S FSP-B28 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.307

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R&S FSP Instrument Functions

Introduction

All functions of the Spectrum Analyzer and their application are explained in detail in this chapter. The sequence of the described menu groups depends on the procedure selected for the configuration and start of a measurement:

1. Resetting the instrument - PRESET key

2. Setting the mode – hotkey bar and LOCAL key

3. Setting the measurement parameters - keys FREQ, SPAN, AMPT, BW, SWEEP, TRIG, TRACE, CAL

4. Selecting and configuring the measurement function - keys MKR, MKR->, MKR FCTN, MEAS, LINES

The instrument functions for general settings, printout and data management are described at the end of this chapter – keys DISP, SETUP, FILE and HCOPY.

The operating concept is described in the Quick Start Guide, chapter 4, “Basic Operation”.

The IEC/IEEE-bus commands (if any) are indicated for each softkey. For a fast overview a list of softkeys with the associated IEC/IEEE-bus commands is given at the end of chapter “Remote Control – Description of Commands”.

An index at the end of the manual serves as further help for the user.

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Page 70

Initial configuration – PRESET Key R&S FSP

R&S FSP Initial Configuration – PRESET Key

PRESET

Using the PRESET key, the R&S FSP can be set to a predefined initial state.

Pressing the PRESET key causes the R&S FSP to enter its initial state according to the following table:

Table 4-1 Initial State of R&S FSP

Parameter Settings

Notes

The settings are selected in a way that the RF input is always protected against overload, provided that the applied signal levels are in the allowed range for the instrument.

The initial instrument state set by the PRESET key can be adapted to arbitrary applications using the STARTUP RECALL function. With this function the STARTUP RECALL data set is loaded upon pressing the PRESET key. For further information refer to section “Saving and

Recalling Data Sets – FILE Key” on page 4.190.

Mode Spectrum

Center frequency) 1,5 GHz / 3,5 GHz / 6,8 GHz / 15 GHz / 20

GHz (R&S FSP-3/-7/-13/-30/-40)

Center frequency step size 0.1 * center frequency

Span 3 GHz / 7 GHz / 13.6 GHz / 30 GHz / 40

GHz (R&S FSP-3/-7/-13/-30/-40)

RF attenuation auto (10 dB)

Reference level -20 dBm

Level range 100 dB log

Level unit dBm

Sweep time auto

Resolution bandwidth auto (3 MHz)

Video bandwidth auto (10 MHz)

FFT filters off

Span / RBW 50

RBW / VBW 0.33

Sweep cont

Trigger free run

Trace 1 clr write

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R&S FSP Initial configuration – PRESET Key

Parameter Settings

Trace 2/3 blank

Detector auto peak

Trace math off

Frequency offset 0 Hz

Reference level offset 0 dB

Reference level position 100 %

Grid abs

Cal correction on

Noise source off

Input RF

Display Full screen, active screen A

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Mode Selection – HOTKEY Bar R&S FSP

Mode Selection – Hotkey Bar

For fast mode selection the R&S FSP has keys located under the measurement screen, the so-called hotkeys. These hotkeys are displayed depending on the options installed on the instrument. According to the selected mode, the corresponding softkey menus are displayed (on the right side of the measurement screen).

Two keys are reserved for the basic model:

SPECTRUM

SCREEN A / SCREEN B

SCREEN B

The SPECTRUM hotkey sets R&S FSP to analyzer mode.

The analyzer mode is the basic setting of R&S FSP.

Remote command: INST:SEL SAN

With the SCREEN A / SCREEN B hotkey two different settings can be selected on the R&S FSP in the FULL SCREEN mode.

In the SPLIT SCREEN mode the key switches between active diagram A and B.

The key designation indicates the diagram which has been activated by means of the key.

The currently active window is marked by or on the right of the diagram.

Remote command: DISP:WIND<1|2>:SEL A

The other keys are described with the corresponding options.

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R&S FSP Return to Manual Control – LOCAL Menu

Return to Manual Control – LOCAL Menu

The LOCAL menu is displayed on switching the instrument to remote control mode.

At the same time, the hotkey bar is blanked out and all keys are disabled except the PRESET key. The diagram, traces and display fields are then blanked out (they can be activated using the remote control command SYSTem:DISPlay: UPDate ON).

The menu contains only one softkey, the LOCAL key. The LOCAL key switches the instrument from remote to manual control, with the assumption that the remote controller has not previously set the LOCAL LOCKOUT function.

A change in the control mode consists of:

– Enabling the Front Panel Keys

Returning to manual mode enables all inactive keys and turns on the hotkey bar. The softkey menu which is displayed is the main menu of the current mode.

Inserting the measurement diagrams

LOCAL

The blanked diagrams, traces and display fields are inserted.

– Generating the message OPERATION COMPLETE

If, at the time of pressing the LOCAL softkey, the synchronization mechanism via *OPC, *OPC? or *WAI is active, the currently running measurement procedure is aborted and synchronization is achieved by setting the corresponding bits in the registers of the status reporting system.

– Setting Bit 6 (User Request) of the Event Status Register

With a corresponding configuration of the status reporting system, this bit immediately causes the generation of a service request (SRQ) which is used to inform the control software that the user wishes to return to front-panel control. This information can be used, e.g., to interrupt the control program so that the user can make necessary manual corrections to instrument settings. This bit is set each time the LOCAL softkey is pressed.

Note

If the LOCAL LOCKOUT function is active in the remote control mode, the front-panel PRESET key is also disabled. The LOCAL LOCKOUT state is left as soon as the process controller de-activates the REN line or the IEC/IEEE-bus cable is disconnected from the instrument.

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Spectrum Analysis – SPECTRUM Hotkey R&S FSP

Analyzer Mode

The analyzer mode is activated by pressing the SPECTRUM hotkey (see also section “Mode Selection – Hotkey Bar” on page 4.8)

SPECTRUM

The SPECTRUM hotkey selects the analyzer mode.

This mode is the default setting of the R&S FSP.

The functions provided correspond to those of a conventional spectrum analyzer. The Spectrum Analyzer measures the frequency spectrum of the test signal over the selected frequency range with the selected resolution and sweep time, or, for a fixed frequency, displays the waveform of the video signal.

Note

If two displays (screen A and screen B) are opened after switch-on of signal analysis, the analyzer mode is only set for the display activated for entry (marked at the top right corner of diagram). For the other display, the previous settings remain valid.

Data acquisition and display of measured values is sequential: first in the upper and then in the lower display.

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R&S FSP Spectrum Analysis – FREQ Key

Frequency and Span Selection – FREQ

The FREQ key is used to specify the frequency axis of the active display window. The frequency axis can be defined either by the start and stop frequency or by the center frequency and the span (SPAN key). With two windows (SPLIT SCREEN) displayed at the same time, the input data always refer to the window selected in the SYSTEM-DISPLAY menu.

After pressing one of the CENTER, START or STOP softkeys, the value of the corresponding parameter can be defined in an input window.

CENTER

CF STEPSIZE

START

STOP

FREQUENCY OFFSET

SIGNAL TRACK

EXTERNAL MIXER

(option B21)

! Span <> 0 Span = 0

! TRACK ON/OFF

0.1 * SPAN 0.1 * RBW

0.5 * SPAN 0.5 * RBW

X * SPAN X * RBW

= CENTER = CENTER

= MARKER = MARKER

MANUAL MANUAL

TRACK BW

TRACK THRESHOLD

SELECT TRACE

CENTER

The CENTER softkey opens the window for manually entering the center frequency.

The allowed range of values for the center frequency is:

• for the frequency domain (span >0): minspan / 2 ≤ f

center

≤ f

max

– minspan / 2

• and for the time domain (span = 0): 0 Hz ≤ f

center frequency

center

minspan smallest selectable span > 0 Hz (10 Hz)

max. frequency

max

center

≤ f

max

Remote command: FREQ:CENT 100MHz

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Spectrum Analysis – FREQ Key R&S FSP

CF STEPSIZE

0.1 * SPAN The 0.1 * SPAN softkey sets the step size for the center frequency entry to 10%

0.5 * SPAN The 0.5 * SPAN softkey sets the step size for the center frequency entry to 50%

X * SPAN The X * SPAN softkey allows the factor defining the center frequency step size

The CF STEPSIZE softkey opens a submenu for setting the step size of the center frequency. The step size can be coupled to the span (frequency domain) or the resolution bandwidth (time domain) or it can be manually set to a fixed value. The softkeys are mutually exclusive selection keys.

The softkeys are presented according to the selected domain (frequency or time).

Softkeys in frequency domain:

of the span.

Remote command: FREQ:CENT:STEP:LINK SPAN

FREQ:CENT:STEP:LINK:FACT 10PCT

of the span.

Remote command: FREQ:CENT:STEP:LINK SPAN

FREQ:CENT:STEP:LINK:FACT 50PCT

to be entered as % of the span.

Remote command: FREQ:CENT:STEP:LINK SPAN

FREQ:CENT:STEP:LINK:FACT 20PCT

= CENTER The = CENTER softkey sets the step size coupling to MANUAL and the step

size to the value of the center frequency. This function is especially useful during measurements of the signal harmonic content because by entering the center frequency each stroke of the STEP key selects the center frequency of another harmonic.

Remote command: --

= MARKER The = MARKER softkey sets the step size coupling to MANUAL and the step

size to the value of the marker. This function is especially useful during measurements of the signal harmonic content at the marker position because by entering the center frequency each stroke of the STEP key selects the center frequency of another harmonic.

Remote command: --

MANUAL The MANUAL softkey activates the window for entering a fixed step size.

Remote command: FREQ:CENT:STEP 120MHz

Softkeys in time domain:

0.1 * RBW The 0.1 * RBW softkey sets the step size for the center frequency entry to 10% of the resolution bandwidth.

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R&S FSP Spectrum Analysis – FREQ Key

AUTO 0.1 * RBW corresponds to the default setting.

Remote command: FREQ:CENT:STEP:LINK RBW

FREQ:CENT:STEP:LINK:FACT 10PCT

0.5 * RBW The 0.5 * RBW softkey sets the step size for the center frequency entry to 50% of the resolution bandwidth.

Remote command: FREQ:CENT:STEP:LINK RBW

FREQ:CENT:STEP:LINK:FACT 50PCT

X * RBW The X * RBW softkey allows the factor defining the center frequency step size

to be entered as % of the resolution bandwidth.

Values between 1 and 100% in steps of 1% are allowed. The default setting is 10%.

Remote command: FREQ:CENT:STEP:LINK RBW

FREQ:CENT:STEP:LINK:FACT 20PCT

= CENTER The = CENTER softkey sets the step size coupling to MANUAL and the step

START

Remote command: --

= MARKER The = MARKER softkey sets the step size coupling to MANUAL and the step

Remote command: --

MANUAL The MANUAL softkey activates the window for entering a fixed step size.

Remote command: FREQ:CENT:STEP 120MHz

The START softkey activates the window for manually entering the start frequency.

The allowed range of values for the start frequency is: 0 Hz ≤ f

start frequency

start

minspan smallest selectable span (10 Hz)

max. frequency

max

start

≤ f

- minspan

max

Remote command: FREQ:STAR 20MHz

STOP

The STOP softkey activates the window for entering the stop frequency.

The allowed range of values for the stop frequency is:

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Spectrum Analysis – FREQ Key R&S FSP

FREQUENCY OFFSET

SIGNAL TRACK

minspan ≤ f

stop frequency

stop

minspan smallest selectable span (10 Hz)

max. frequency

max

stop

≤ f

max

Remote command: FREQ:STOP 2000MHz

The FREQUENCY OFFSET softkey activates the window for entering an arithmetical frequency offset which is added to the frequency axis labelling. The allowed range of values for the offset is -100 GHz to 100 GHz. The default setting is 0 Hz.

Remote command: FREQ:OFFS 10 MHz

The SIGNAL TRACK softkey switches on the tracking of a signal near the center frequency. The signal is tracked as long it is in the search bandwidth around the center frequency defined with TRACK BW and above the level threshold defined with TRACK THRESHOLD.

For that purpose, the maximum signal is searched (PEAK SEARCH) on the screen and the center frequency set to this signal (MARKER ->CENTER) after each frequency sweep within the search bandwidth.

If the signal falls below the level threshold or jumps out of the search bandwidth around the center frequency, the center frequency is not varied until a signal is in the search bandwidth above the level threshold. This can be achieved by manually modifying the center frequency, for example.

On switching on, the softkey is highlighted and the search bandwidth and the threshold value are marked on the diagram by two vertical lines and one horizontal line. All these lines are allocated the designation TRK.

At the same time a submenu is opened in which the search bandwidth, the threshold value and the trace can be modified for the maximum search.

The softkey is only available in the frequency domain (span >0).

Remote command: CALC:MARK:FUNC:STR OFF

TRACK ON/OFF The TRACK ON/OFF softkey switches on and off signal tracking.

Remote command: CALC:MARK:FUNC:STR OFF

TRACK BW The TRACK BW softkey defines the search bandwidth for signal tracking. The

frequency range is symmetrical with respect to the center frequency.

Remote command: CALC:MARK:FUNC:STR:BAND 10KHZ

TRACK THRESHOLD The TRACK THRESHOLD softkey defines the threshold value for signal

detection. The value is always entered as an absolute level value.

Remote command: CALC:MARK:FUNC:STR:THR -70DBM

SELECT TRACE The SELECT TRACE softkey selects the trace on which signal tracking is to be

performed.

Remote command: CALC:MARK:FUNC:STR:TRAC 1

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R&S FSP Spectrum Analysis – SPAN Key

Setting the Frequency Span – SPAN

The SPAN key opens a menu which offers various options for setting the span.

The entry of the span (SPAN MANUAL softkey) is automatically active for span > 0 Hz.

For span = 0 Hz the entry for sweep time (SWEEPTIME MANUAL) is automatically active.

With two windows (SPLIT SCREEN) displayed at the same time, the input data always refer to the window selected with the SCREEN A/B hotkey.

SPAN MANUAL

SPAN

MANUAL

SWEEPTIME

MANUAL

FULL SPAN

ZERO SPAN

LAST SPAN

FREQ AXIS LIN LOG

. . .

The SPAN MANUAL softkey activates the window for manually entering the frequency span. The center frequency is kept constant.

The allowed range of span values is

• for the time domain (span = 0): 0 Hz

• and for the frequency domain (span >0): minspan ≤ f

frequency span

span

minspan smallest selectable span (10 Hz)

max. frequency

max

span

≤ f

max

Remote command: FREQ:SPAN 2GHz

SWEEPTIME MANUAL

The SWEEPTIME MANUAL softkey activates the window for entering the sweep time manually with Span = 0 Hz. The softkey is not available for Span > 0 Hz.

Remote command: SWE:TIME 10s

FULL SPAN

The FULL SPAN softkey sets the span to the full frequency range of R&S FSP.

Remote command: FREQ:SPAN:FULL

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Spectrum Analysis – SPAN Key R&S FSP

ZERO SPAN

LAST SPAN

FREQ AXIS LIN/ LOG

The ZERO SPAN softkey sets the span to 0 Hz. The x axis becomes the time axis with the grid lines corresponding to 1/10 of the current sweep time (SWT).

Remote command: FREQ:SPAN 0Hz

After changing the span setting the LAST SPAN softkey activates the previous setting. With this function a fast change between overview measurement (FULL SPAN) and detailed measurement (manually set center frequency and span) is possible.

Remote command: --

The FREQ AXIS LIN/LOG softkey switches between linear and logarithmic scaling of the frequency axis. Switch over is only possible if the stop/start frequency ratio is ≥10.

The default state is LIN.

Note

Only values > 0 Hz are restored, i.e. a transition between time and frequency domain is not possible.

The logarithmic frequency axis is only available in analyzer mode and it is not available in zero span mode, in external mixer mode, with frequency offset or if the ratio stop frequency / start frequency is below 1.4.

Remote command: DISP:WIND<1|2>:TRAC:X:SPAC LIN

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R&S FSP Spectrum Analysis – AMPT Key

Level Display Setting and RF Input Configuration – AMPT

The AMPT key is used to set the reference level, the maximum level and the display range of the active window as well as the input impedance and the input attenuation of the RF input.

The AMPT key opens a menu for setting the reference level and the input attenuation of the active window. The data entry for the reference level (REF LEVEL softkey) is opened automatically.

Further settings regarding level display and attenuation can be made in this menu.

REF LEVEL

RANGE LOG 100 dB

RANGE LOG MANUAL

RANGE LINEAR

UNIT

! dBm

RF ATTEN MANUAL

RF ATTEN AUTO

MIXER

! MIXER LOW NOISE

Side menu

REF LEVEL POSITION

REF LEVEL OFFSET

GRID ABS/REL

! RANGE LINEAR %

RANGE LINEAR dB

dBmV

dBµV

dBµΑ

dBµW

VOLT

AMPERE

WATT

EL ATTEN AUTO (option B25)

EL ATTEN MANUAL (option B25)

EL ATTEN OFF (option B25)

RF INPUT 50 W / 75 W

REF LEVEL

The REF LEVEL softkey allows the reference level to be input in the currently active unit (dBm, dBµV, etc.)

Remote command: DISP:WIND:TRAC:Y:RLEV -60dBm

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Spectrum Analysis – AMPT Key R&S FSP

RANGE LOG 100 dB

RANGE LOG MANUAL

RANGE LINEAR

RANGE LINEAR % The RANGE LINEAR % softkey selects linear scaling in % for the level display

The RANGE LOG 100 dB softkey sets the level display range to 100 dB.

Remote command: DISP:WIND:TRAC:Y:SPAC LOG

DISP:WIND:TRAC:Y 100DB

The RANGE LOG MANUAL softkey activates the manual entry of the level display range. Display ranges from 1 to 200 dB are allowed in 10 dB steps. Inputs which are not allowed are rounded to the next valid value.

The default setting is 100 dB.

Remote command: DISP:WIND:TRAC:Y:SPAC LOG

DISP:WIND:TRAC:Y 120DB

The RANGE LINEAR softkey selects linear scaling for the level display range of the Spectrum Analyzerr. In addition, it opens a submenu for selecting % or dB for the scaling.

When linear scaling is selected, the % scaling is first activated (see also RANGE LINEAR dB softkey).

Remote command: DISP:WIND:TRAC:Y:SPAC LIN

range, i.e. the horizontal lines are labelled in %. The grid is divided in decadic steps. Markers are displayed in the selected unit; delta markers are displayed in % referenced to the voltage value at the position of marker 1.

Remote command: DISP:WIND:TRAC:Y:SPAC LIN

RANGE LINEAR dB The RANGE LINEAR dB softkey selects linear scaling in dB for the level display

range, i.e. the horizontal lines are labelled in dB.

Markers are displayed in the selected unit; delta markers are displayed in dB referenced to the power value at the position of marker 1.

Remote command: DISP:WIND:TRAC:Y:SPAC LDB

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R&S FSP Spectrum Analysis – AMPT Key

UNIT

The UNIT softkey opens a submenu allowing to select the unit for the level axis.

RF ATTEN MANUAL

The default setting is dBm.

In general, the Spectrum Analyzer measures the signal voltage at the RF input. The level display is calibrated in rms values of an unmodulated sinewave signal. In the default state, the level is displayed at a power of 1 mW (= dBm). Via the known input resistance of 50 Ω or 75W, conversion to other units is possible. The units dBm, dBmV, dBµV, dBµA, dBpW, V, A and W are directly convertible.

Remote command: CALC:UNIT:POW DBM

The RF ATTEN MANUAL softkey allows the attenuation to be entered irrespective of the reference level.

The attenuation can be set in 10 dB steps between 0 and 70 dB (in 5 dB steps between 0 and 75 dB if option B25, Electronic Attenuator, is fitted).

Other entries will be rounded to the next lower integer value.

If the defined reference level cannot be set for the given RF attenuation, the reference level will be adjusted accordingly and the warning "Limit reached" will be output.

Note

The 0 dB value can be entered only via the numeric keypad in order to protect the input mixer against overload.

Remote command: INP:ATT 40 DB

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Spectrum Analysis – AMPT Key R&S FSP

RF ATTEN AUTO

MIXER LEVEL

MIXER

MIXER LOW NOISE The MIXER LOW NOISE softkey changes the operating point of the input mixer

The RF ATTEN AUTO softkey sets the RF attenuation automatically as a function of the selected reference level.

This ensures that the optimum RF attenuation desired by the user is always used.

RF ATTEN AUTO is the default setting.

Remote command: INP:ATT:AUTO ON

The MIXER LEVEL softkey opens the submenu for changing the mixer level at the input mixer.

The MIXER softkey opens a submenu for defining the maximum mixer level attainable for the selected reference level.

so that (with the RF attenuation remaining the same) the inherent noise of the Spectrum Analyzer is reduced compared to the default setup. If the softkey is enabled, the Spectrum Analyzer has an improved dynamic range above 3 GHz.

Notes

• The function is available for models 13, 30 and 40.

REF LEVEL POSITION

REF LEVEL OFFSET

• The modified operating point of the input mixer will be effective only if the start frequency of the Spectrum Analyzer is ≥3 GHz.

• In the default setting, the function is switched off.

Remote command: INP:ATT:AUTO:MODE LNO

The REF LEVEL POSITION softkey allows the reference level position to be entered.

The setting range is from -200 to +200%, 0% corresponding to the lower and 100% to the upper limit of the diagram.

Remote command: DISP:WIND:TRAC:RPOS 100PCT

The REF LEVEL OFFSET softkey allows the arithmetic level offset to be entered. This offset is added to the measured level irrespective of the selected unit. The scaling of the Y axis is changed accordingly.

The setting range is ±200 dB in 0.1 dB steps.

Remote command: DISP:WIND:TRAC:RLEV:OFFS -10dB

GRID ABS/REL

1164.4556.12 4.20 E-2

The GRID ABS/REL softkey switches between absolute and relative scaling of the level axis.

GRID ABS is the default setting.

ABS The labelling of the level lines refers to the absolute value of the

reference level.

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R&S FSP Spectrum Analysis – AMPT Key

REL The upper line of the grid is always at 0 dB.

The scaling is in dB whereas the reference level is always in the set unit (dBm, dBmV,..).

For setting RANGE LINEAR (linear scaling, labelling of axes in %) the softkey is not displayed since the unit % itself implies a relative scale.

Remote command: DISP:WIND:TRAC:Y:MODE ABS

RF INPUT 50 Ω / 75 Ω

EL ATTEN MANUAL

The RF INPUT 50Ω / 75Ω softkey switches the input impedance of the instrument between 50 Ω (= default setting) and 75 Ω.

The setting 75 Ω should be used if the input impedance (50 Ω) is transformed to 75 Ω using the corresponding adapter unit of type RAZ (= 25 Ω in series to the input impedance of the Spectrum Analyzer). The correction value used for the adoption is 1.76 dB = 10 log (75Ω / 50Ω).

All levels specified in this operating manual refer to the default setting of the instrument (50 Ω).

Remote command: INP:IMP 50OHM

Electronic Attenuator

Besides the mechanical attenuator at the RF input, the R&S FSP also offers an electronic attenuation setting (option ELECTRONIC ATTENUATOR B25). The attenuation range is 0 to 30 dB, with the default attenuation being preset by the mechanical attenuator.

The EL ATTEN MANUAL softkey switches the electronic attenuator on and allows the attenuation of the electronic attenuator to be set.

The attenuation can be varied in 5 dB steps from 0 to 30 dB. Other entries are rounded to the next lower integer value.

If the defined reference level cannot be set for the given RF attenuation, the reference level will be adjusted accordingly and the warning "Limit reached" will be output.

Remote command: INP:EATT:AUTO OFF

INP:EATT 10 DB

This function is only available with option ELECTRONIC ATTENUATOR B25.

EL ATTEN AUTO

1164.4556.12 4.21 E-2

The EL ATTEN AUTO softkey switches the electronic attenuator on and automatically sets its attenuation to 0 dB.

The allowed setting range of the reference level ranges from the current reference level on switching on the electronic attenuator to over 30 dB. If a reference level is set outside the allowed 30-dB range, setting is performed by means of the mechanical attenuator. From this new reference level to over 30 dB the setting is again performed with the electronic attenuator.

Remote command: INP:EATT:AUTO ON

This function is only available with option ELECTRONIC ATTENUATOR B25.

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Spectrum Analysis – AMPT Key R&S FSP

EL ATTEN OFF

The EL ATTEN OFF softkey switches the electronic attenuator off.

Remote command: INP:EATT:STAT OFF

This function is only available with option ELECTRONIC ATTENUATOR B25.

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Page 87

R&S FSP Spectrum Analysis – BW Key

Setting the Bandwidths and Sweep Time – BW

The BW key calls a menu for setting the resolution bandwidth (RBW), video bandwidth (VBW) and sweep time (SWT) for the frequency sweep. The parameters may be coupled dependent on the span (stop minus start frequency) or freely set by the user. When working with a split screen display, the settings always refer to the active window.

The R&S FSP offers resolution bandwidths from 10 Hz to 10 MHz in 1, 3, 10 steps:

Resolution bandwidths up to 100 kHz are realized using digital bandpasses with Gaussian characteristics. As far as the attenuation characteristic is concerned they behave like analog filters but have a much higher measurement speed than comparable analog filters. This is due to the fact that the transient response can be compensated as a result of an accurately defined filter behavior.

Bandwidths above 100 kHz are realized using decoupled 4-circuit LC filters.

As an alternative to the analog filters, FFT filters are available for the bandwidths between 1 Hz and 30 kHz. When working with bandwidths up to 30 kHz, the FFT algorithm offers considerably higher measurement speeds with all the other settings remaining the same. The reason is that with analog filters the sweep time required for a particular span is proportional to (Span/RBW using the FFT algorithm, however, the sweep time is proportional to (Span/ RBW).

). When

The video bandwidths are available in 1, 3, 10 steps between 1 Hz and 10 MHz. They can be set in accordance with the resolution bandwidth.

The video filters serve for smoothing the displayed trace. Video bandwidths that are small compared to the resolution bandwidth average out noise peaks and pulsed signals, so that only the signal average is displayed. If pulsed signals are to be measured, it is recommended to use a video bandwidth that is large compared to the resolution bandwidth (VBW ≥ 10 × RBW) for the amplitudes of pulses to be measured correctly.

Note

For analog and digital filters, the R&S FSP has overload reserves of different magnitude above the reference level. Due to the LO breakthrough the overload display OVLD responds with digital filters with RBW < 100 kHz, as soon as the start frequency is selected <6 * resolution bandwidth, for RBW = 100 kHz, as soon as the start frequency is below 3 MHz.

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Page 88

Spectrum Analysis – BW Key R&S FSP

MEAS

SWEEP

TRIG

RES BW MANUAL

VIDEO BW

MANUAL

SWEEPTIME

MANUAL

RES BW

AUTO

VIDEO BW

AUTO

SWEEPTIME

AUTO

COUPLING

RATIO

DEFAULT

COUPLING

FILTER

TYPE

VBW MODE

LIN LOG

RBW / VBW

SINE [1/3]

RBW / VBW

PULSE[0.1]

RBW / VBW

NOISE [10]

RBW / VBW

MANUAL

SPAN /RBW AUTO [50]

SPAN /RBW

MANUAL

RES BW MANUAL

The BW key opens a menu for setting the resolution bandwidth, the video bandwidth, the sweep time and their couplings.

The …BW AUTO softkeys are used to couple the functions. The coupling ratios are selected by means of the COUPLING RATIO softkey.

The …BW MANUAL softkeys allow a parameter to be entered. This parameter is not coupled to the other parameters.

The RES BW MANUAL softkey activates the manual data entry for the resolution bandwidth.

The resolution bandwidth can be selected in 1/3/10 steps in the range between 10 Hz and 10 MHz. The nominal resolution bandwidth is the 3 dB bandwidth.

Note

With the …BW AUTO softkeys the resolution bandwidth, the video bandwidth and the sweep time can be entered separately for the frequency domain (span > 0 Hz) and the time domain (span = 0 Hz).

But with …BW MANUAL softkeys the selected values apply to both the frequency and time domain.

When FFT filters are used, the lower limit of the bandwidth is 1 Hz. FFT filters may be used with bandwidths up to 30 kHz.

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R&S FSP Spectrum Analysis – BW Key

For numeric inputs, the values are always rounded to the nearest possible bandwidth. For rotary knob or UP/DOWN key inputs, the bandwidth is adjusted in steps either upwards or downwards.

For filter type CHANNEL or RRC the bandwidth is selected from the list of available channel filters given at the end of this section. For data entry, the cursor keys Uu and Ud scroll through this list.

The manual input mode of the resolution bandwidth is indicated by a green asterisk (*) on the display.

Remote command: BAND:AUTO OFF;

BAND 1MHz

VIDEO BW MANUAL

SWEEP TIME MANUAL

The VIDEO BW MANUAL softkey activates the manual data entry for the video bandwidth.

The video bandwidth can be selected in 1/3/10 steps in the range between 1 Hz and 10 MHz.

For numeric inputs, the values are always rounded to the nearest possible allowed bandwidth. For rotary knob or UP/DOWN key inputs, the bandwidth is adjusted in steps either downwards or upwards.

The manual input mode of the video bandwidth is indicated by a green asterisk (*) on the display.

Remote command: BAND:VID:AUTO OFF;

BAND:VID 10 kHz

The SWEEPTIME MANUAL softkey activates the manual data entry for the sweep time. At the same time, the coupling of the sweep time is cancelled. Other couplings (VIDEO BW, RES BW) remain effective.

In the frequency domain (span > 0 Hz) and for resolution bandwidths above 1 kHz, the allowed sweep times for spans > 3.2 kHz range from 2.5 ms through to 16000 s. With spans below 3.2 kHz, the maximum allowed sweep time is reduced to 5 s * span/Hz.

If FFT filters are used, the sweep time is fixed by the span and the bandwidth and therefore cannot be set.

In time domain (span = 0 Hz), the range of sweep times is 1 µs to 16000 s is selectable in steps of max. 5% of the sweep time. For numeric inputs, rounding is made to the nearest possible sweep time. For rotary knob or UP/DOWN key inputs, the sweep time is adjusted in steps either downwards or upwards.

The manual input mode of the sweep time is indicated by a green asterisk (*) on the display. If the selected sweep time is too short for the selected bandwidth and span, level measurement errors will occur. This happens because the available settling time for the resolution or video filters is too short. In this case, the R&S FSP outputs UNCAL on the display and marks the indicated sweep time with a red asterisk (*).

Remote command: SWE:TIME:AUTO OFF;

SWE:TIME 10s

RES BW AUTO

1164.4556.12 4.25 E-2

The RES BW AUTO softkey couples the resolution bandwidth to the selected span. Changing the span causes automatic adjustment of the resolution bandwidth.

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Spectrum Analysis – BW Key R&S FSP

Automatic coupling of resolution bandwidth to span is always recommended when a favorable setting of the resolution bandwidth in relation to the selected span is desired for the measurement under request.

The coupling ratio is set in the COUPLING RATIO submenu.

The RES BW AUTO softkey is only available in the frequency domain (span > 0 Hz). The softkey is blanked in the time domain.

Remote command: BAND:AUTO ON

VIDEO BW AUTO

SWEEPTIME AUTO

The VIDEO BW AUTO softkey couples the video bandwidth to the resolution bandwidth. If the resolution bandwidth is changed, the video bandwidth is automatically adjusted.

The coupling of the video bandwidth is always recommended when the minimum sweep time is required for a selected resolution bandwidth. Narrower video bandwidths require longer sweep times due to the longer settling time. Wider bandwidths reduce the signal/noise ratio.

The coupling ratio is set in the COUPLING RATIO submenu.

The coupling of the video bandwidth to the resolution filter is also permitted for the time domain display (span = 0).

Remote command: BAND:VID:AUTO ON

The SWEEPTIME AUTO softkey couples the sweep time to the span, video bandwidth (VBW) and resolution bandwidth (RBW). The sweep time is automatically adjusted on any change in span, resolution bandwidth or video bandwidth.

The softkey is only available in the frequency domain (span >0 Hz). It is blanked in the time domain.

The R&S FSP always selects the shortest sweep time possible without falsifying the signal. The maximum level error compared to using a longer sweep time is < 0.1 dB. If additional bandwidth and level errors are to be avoided, the sweep time is to be set to three times the time offered in coupled mode.

Remote command: SWE:TIME:AUTO ON

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R&S FSP Spectrum Analysis – BW Key

COUPLING RATIO

The COUPLING RATIO softkey opens a submenu for selection of the coupling ratios.

When the default setting is active, i.e. the COUPLING RATIO softkey is deactivated (not highlighted), the ratio span/resolution bandwidth (SPAN/RBW) is 50 (this corresponds to SPAN / RBW AUTO [50]) and the ratio resolution bandwidth/video bandwidth (RBW/VBW) is 0.33 (this corresponds to RBW / VBW SINE [1/3]).

If the ratio RBW/VBW or SPAN/RBW is different from the default setting, the COUPLING RATIO softkey is highlighted.

The softkeys RBW/VBW... are selection keys. Only one softkey can be enabled at any one time. The softkeys are only effective for the VBW AUTO selection in the main menu.

The softkeys SPAN/RBW... are also selection keys. They are only effective for the RBW AUTO selection in the main menu.

RBW/VBW SINE [1/3] The RBW/VBW SINE [1/3] softkey sets the following coupling ratio:

video bandwidth = 3 × resolution bandwidth.

This is the default setting for the coupling ratio resolution bandwidth/video bandwidth.

This is the coupling ratio recommended if sinusoidal signals are to be measured.

Remote command: BAND:VID:RAT 3

This setting is only effective for the VBW AUTO selection in the main menu.

RBW/VBW

PULSE [.1]

1164.4556.12 4.27 E-2

The RBW/VBW PULSE [.1] softkey sets the following coupling ratio: video bandwidth = 10 × resolution bandwidth or

video bandwidth = 10 MHz (= max. VBW).

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Spectrum Analysis – BW Key R&S FSP

This coupling ratio is recommended whenever the amplitudes of pulsed signals are to be measured correctly. The IF filter is exclusively responsible for pulse shaping. No additional evaluation is performed by the video filter.

Remote command: BAND:VID:RAT 10

This setting is only effective for the VBW AUTO selection in the main menu.

RBW/VBW

NOISE [10]

RBW/VBW MANUAL The RBW/VBW MANUAL softkey activates the manual input of the coupling

SPAN/RBW

AUTO [50]

The RBW/VBW NOISE [10] softkey sets the following coupling ratio: video bandwidth = resolution bandwidth/10

At this coupling ratio, noise and pulsed signals are suppressed in the video domain. For noise signals, the average value is displayed.

Remote command: BAND:VID:RAT 0.1

This setting is only effective for the VBW AUTO selection in the main menu.

ratio.

The resolution bandwidth/video bandwidth ratio can be set in the range 0.001 to 1000.

Remote command: BAND:VID:RAT 10

This setting is only effective for the VBW AUTO selection in the main menu.

The SPAN/RBW AUTO [50] softkey sets the following coupling ratio: resolution bandwidth = span/50

This coupling ratio is the default setting of the R&S FSP

Remote command: BAND:RAT 0.02

This setting is only effective for the RBW AUTO selection in the main menu.

SPAN/RBW MANUAL The SPAN/RBW MANUAL softkey activates the manual input of the coupling

ratio.

The span / resolution bandwidth ratio can be set in the range 1 to 10000.

Remote command: BAND:RAT 0.1

This setting is only effective for the RBW AUTO selection in the main menu.

DEFAULT COUPLING

The DEFAULT COUPLING softkey sets all coupled functions to the default state (AUTO). In addition, the ratio RBW/VBW is set to SINE [1/3] and the ratio SPAN/

RBW to 50 in the COUPLING RATIO submenu (default setting, COUPLING RATIO softkey not highlighted).

Remote command: BAND:AUTO ON

BAND:VID:AUTO ON SWE:TIME:AUTO ON

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R&S FSP Spectrum Analysis – BW Key

FILTER TYPE

The FILTER TYPE softkey opens the selection list for different filter types. In the range up to 30 kHz digital band filters with Gaussian characteristic and filtering with FFT algorithm can be selected.

FILTER TYPE

NORMAL

FFT CHANNEL RRC

Filter Types

• NORMAL (3dB): The resolution bandwidths are implemented by Gaussian filters with the set 3 dB bandwidth and correspond approximately to the noise bandwidth. For bandwidths up to 100 kHz, digital bandpass filters are used.

• FFT: An FFT is performed. For that purpose, the filtered IF signal is digitized and then transformed into the spectral domain via FFT. The transformation range depends on the selected filter bandwidths and can be set between 4 kHz to 50 kHz. If the span is larger than the transformation range, several transformations are performed and the results are appended to each other in the spectral domain.

If the span is smaller than the transformation range, the measurement results are interpolated when the number of measurement points provided by the FFT is smaller than the number of display points in x-direction (501). A flattop window serves as a window in the time domain so that high amplitude precision with good selection is achieved.

Compared to bandpasses, FFT filters lead to significantly reduced sweep times. For a span of 50 kHz and a bandwidth of 100 Hz, for instance, the sweep time is reduced from 5 s to 40 ms. FFT filters are particularly suitable for stationary signals (sinusoidal signals or signals that are continuously modulated in time). For burst signals (TDMA) or pulsed signals, normal filters are preferable.

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Spectrum Analysis – BW Key R&S FSP

Additionally, a number of especially steep-edged channel filters are available for power measurement since firmware version 1.10.

A distinction is made between the following filter types:

• CHANNEL = general, steep-edged channel filters

Note

As soon as the FFT filters are active (RBW ≤ 30 kHz) the sweep time display field (SWT) is replaced by the acquisition time (AQT) display field.

FFT is a block transformation so the result depends on the time relation between the data set to be transformed and the burst or pulsed signal. A gated sweep measurement for TDMA signals is therefore not provided if FFT filters are used.

When the tracking generator (option R&S FSP-B9) is used as signal source for the DUT, filtering with the FFT algorithm is not useful. The selection FFT is thus not available if the tracking generator is switched on.

• RRC = filters with root-raised cosine characteristic (RRC = Root Raised Cosine)

When selecting these filter types, the automatic coupling of the resolution bandwidth to the span is not available. The filters are selected via the RES BW softkey.

A list of all available channel filters with their associated applications can be found at the end of this section.

Remote command: SENS:BAND:RES:TYPE NORM | FFT | CFIL

| RRC

List of Available Channel Filters

The channel filters included in the following table can be activated via the

FILTER TYPE softkey and are then available as resolution filters (softkey RES BW)

They are available for firmware version 1.10 or higher.

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R&S FSP Spectrum Analysis – BW Key

Note

For filters of type RRC (Root Raised Cosine), the filter bandwidth indicated describes the sampling rate of the filter.

For all other filters (CFILter) the filter bandwidth is the 3 dB bandwidth.

Filter Bandwidth Filter Type Application

100 Hz

200 Hz

300 Hz

500 Hz

1 kHz

1.5 kHz

2 kHz

2.4 kHz

2.7 kHz

3 kHz

3.4 kHz

4 kHz

4.5 kHz

5 kHz

6 kHz

8.5 kHz

9 kHz

CFILter

SSB

DAB, Satellite

ETS300 113 (12.5 kHz channels)

AM Radio

10 kHz

12.5 kHz

14 kHz

15 kHz

16 kHz 18 kHz, α=0.35

20 kHz

21 kHz

24.3 kHz, α=0.35

25 kHz

30 kHz

50 kHz

CFILter

RRC

CFILter

RRC

CFILter

CDMAone

ETS300 113 (20 kHz channels)

ETS300 113 (25 kHz channels)

TETRA

PDC

IS 136

CDPD, CDMAone

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Spectrum Analysis – BW Key R&S FSP

Filter Bandwidth Filter Type Application

VBW MODE LIN/ LOG

100 kHz

150 kHz

192 kHz

200 kHz

300 kHz

500 kHz

1.0 MHz

1.2288 MHz

1.5 MHz

2.0 MHz *)

3.0 MHz *)

3.84 MHz, a=0.22 *)

4.096 MHz, a=0.22 *)

5.0 MHz *)

5.6 MHz

6 MHz

6.4 MHz

*) This filter is avaible with modification index > 2 of the IF filter module (see softkey SETUP - SYSTEM INFO - HARDWARE INFO).

CFILter

RRC

CFILter

FM Radio

PHS

J.83 (8-VSB DVB, USA)

CDMAone

DAB

W-CDMA 3GPP

W-CDMA NTT DOCoMo

DVB-T (Japan)

J.83 (8VSB DVB, USA)

DVB-T

The VBW MODE LIN/LOG softkey determines the position of the video filter in the signal path for resolution bandwidths ≤ 100 kHz:

• If LINear is selected, the video filter will be in front of the logarithmic amplifier (default).

• If LOGarithmic is selected, the video filter will be behind the logarithmic amplifier.

The essential difference between the two operating modes relates to the settling in the case of falling signal edges:

With LINear, the falling signal edge will be "flatter" than with LOGarithmic.

This is due to the conversion from linear power to logarithmic level units: a reduction of the linear power by 50% reduces the logarithmic signal level by only 3 dB.

Remote command: BAND:VID:TYPE LIN

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R&S FSP Spectrum Analysis – SWEEP Key

Sweep Settings – SWEEP

The SWEEP key serves for configuring the sweep mode.

The SWEEP key calls a menu in which the sweep mode is defined. In splitscreen mode, the entries made are valid for the active window only.

The CONTINUOUS SWEEP, SINGLE SWEEP and SGL SWEEP DISP OFF softkeys are mutually exclusive selection keys.

CONTINUOUS SWEEP

MEAS

SWEEP

TRIG

CONTINUOUS

SWEEP

SINGLE

SWEEP

CONTINUE

SGL SWEEP

SWEEPTIME

MANUAL

SWEEPTIME

AUTO

SWEEP COUNT

SWEEP

POINTS

SGL SWEEP

DISP OFF

The CONTINUOUS SWEEP softkey activates the continuous sweep mode, which means that the sweep takes place continuously according to the trigger mode set.

When working in the split-screen mode and with different settings in the two windows, screen A is swept first, followed by screen B. When the softkey is pressed, the sweep is restarted.

CONTINUOUS SWEEP is the default setting of R&S FSP.

Remote command: INIT:CONT ON

SINGLE SWEEP

The SINGLE SWEEP softkey starts n sweeps after triggering. The number of sweeps is determined by the SWEEP COUNT softkey.

When working in the split-screen mode, the frequency ranges of the two windows are swept one after the other.

If a trace is swept using TRACE AVERAGE or MAXHOLD, the value set via the SWEEP COUNT softkey determines the number of sweeps. If 0 has been entered, one sweep is performed.

Remote command: INIT:CONT OFF

CONTINUE SGL SWEEP

The CONTINUE SGL SWEEP softkey repeats the number of sweeps set under SWEEP COUNT, however without first deleting the trace.

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Spectrum Analysis – SWEEP Key R&S FSP

This is particularly of interest when using the functions TRACE AVERAGE and MAXHOLD, if previously recorded measurement results are to be taken into

consideration for averaging / maximum search.

If SGL SWEEP DISP OFF is active, the screen is switched off also during repeated sweeps.

Remote command: INIT:CONM

SWEEPTIME MANUAL

SWEEPTIME AUTO

SWEEP COUNT

The SWEEPTIME MANUAL softkey activates the window for entering the sweep time manually (see also BW menu).

Remote command: SWE:TIME 10s

The SWEEPTIME AUTO softkey activates the automatic selection of the sweep time as a function of the bandwidth of the resolution and video filters (see also BW menu).

Remote command: SWE:TIME:AUTO ON

The SWEEP COUNT softkey activates the window for the entry of the number of sweeps to be performed by R&S FSP after a single sweep has been started. If Trace Average, Max Hold or Min Hold is activated, this also determines the number of averaging or maximum search procedures.

Example

[TRACE1: MAX HOLD] [SWEEP: SWEEP COUNT: {10} ENTER] [SINGLE SWEEP]

R&S FSP performs the Max Hold function over 10 sweeps.

The permissible range for the sweep count is 0 to 32767. For sweep count = 0 or 1, one sweep is performed. For trace averaging in the continuous-sweep mode, R&S FSP performs running averaging over 10 sweeps if sweep count = 0; if sweep count = 1, no averaging is performed.

The sweep count is valid for all the traces in a diagram.

Remote command: SWE:COUN 64

SWEEP POINTS

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The SWEEP POINTS softkey selects the number of measurement samples acquired during a sweep.

Note

The number of sweeps set in the TRACE menu is the same as that in the SWEEP menu.

If SINGLE SWEEP is selected, the measurement stops after the selected number of sweeps has been performed.

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R&S FSP Spectrum Analysis – SWEEP Key

The following numbers of points per sweep are available: 125, 251, 501 (default), 1001, 2001, 4001, 8001, 16001, 32001

SGL SWEEP DISP OFF

Remote command: SWE:POIN 501

The SGL SWEEP DISP OFF softkey deactivates the display while a single sweep is being performed. Once the sweep has been completed, the trace is shown.

Remote command: INIT:DISP OFF;:INIT

Note

The autopeak detector will be disabled while the number of points per sweep is ≠ 501.

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Spectrum Analysis – TRIG Key R&S FSP

Triggering the Sweep – TRIG

The TRIG key opens a menu for selection of the various trigger sources, trigger polarity and external gate function. The active trigger mode is indicated by highlighting the corresponding softkey.

For video trigger, a trigger threshold can be entered, which is represented in the diagram as a horizontal line.

To indicate that a trigger mode other than FREE RUN has been set, the enhancement label TRG is displayed on the screen. If two windows are displayed, TRG appears next to the appropriate window.

The option TV and RF Trigger (R&S FSP-B6) adds a number of trigger functions for the analysis of TV signals to this menu (see section “Option

R&S FSP-B6 – TV and RF Trigger” on page 4.43).

Option FSP-B6

TRIG

Option FSP-B6

FREE RUN

VIDEO

EXTERN

IF POWER

RF POWER

TRIGGER

OFFSET

POLARITY

POS NEG

GATED

TRIGGER

GATE

SETTINGS

TV TRIG

SETTINGS

DELAY COMP

ON OFF

TV TRIGGER

ON OFF

VERT SYNC

VERT SYNC ODD FIELD

VERT SYNC

EVEN FIELD

HOR SYNC

VIDEO POL POS NEG

LINES

625 525

CCVS

INT EXT

GATE MODE

LEVEL EDGE

POLARITY

POS NEG

GATE

DELAY

GATE

LENGTH

SWEEPTIME

FREE RUN

The FREE RUN softkey activates the free-run sweep mode, i.e. start of a sweep is not triggered. Once a measurement is completed, another is started immediately.

FREE RUN is the default setting of R&S FSP.

Remote command: TRIG:SOUR IMM

VIDEO

The VIDEO softkey activates triggering through the displayed voltage.

For the video triggering mode, a horizontal trigger line is shown in the diagram. It may be used to set the trigger threshold between 0% and 100% of the overall diagram height.

Remote command: TRIG:SOUR VID

TRIG:LEV:VID 50 PCT

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Rohde and Schwarz FSP40 Operating Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Tabbed Divider Overview

Documentation Overview

1 Putting into Operation

2 Getting Started

Introduction

Measuring the Spectra of Complex Signals

Intermodulation Measurements

Measuring Signals in the Vicinity of Noise

Noise Measurements

Measuring noise power density

Measurement of Noise Power within a Transmission Channel

Measuring Phase Noise

Measurements on Modulated Signals

Measurements on AM signals

Measurements on FM Signals

Measuring Channel Power and Adjacent Channel Power

Amplitude distribution measurements

3 Manual Control

4 Instrument Functions

Introduction

Analyzer Mode