UBS Axcera DT835A-6 User Manual

INSTRUCTION MANUAL

DT835A

DIGITAL

UHF TRANSMITTER

AXCERA, LLC

103 FREEDOM DRIVE P.O. BOX 525 LAWRENCE, PA 15055-0525 USA

(724) 873-8100 • FAX (724) 873-8105

www.axcera.com • info@axcera.com

Digital UHF Transmitter Table of Contents

TABLE OF CONTENTS

CHAPTER 1 INTRODUCTION Section Page

1.1 Manual Overview..................................................................................1-1

1.2 Safety.................................................................................................1-1

1.3 Maintenance ........................................................................................1-2

1.4 Material Return Procedure .....................................................................1-2

1.5 Limited One-Year Warranty for Axcera Products.......................................1-3

CHAPTER 2 SYSTEM DESCRIPTION AND CUSTOMER REMOTE CONNECTIONS

2.1 System Overview .................................................................................2-1

2.1.1 Single UHF Exciter Assembly ........................................................2-1

2.1.2 (Optional) 10 MHz Reference Distribution Amplifier Tray..................2-2

2.1.3 DM8-R Modulator Tray.................................................................2-2

2.1.4 Amplifier Array Assemblies...........................................................2-2

2.1.5 Transmitter Output Assemblies.....................................................2-3

2.1.6 Control and Status ......................................................................2-3

2.1.7 Metering Panel............................................................................2-4

2.1.8 UHF Exciter Tray .........................................................................2-5

2.1.9 Variable Gain/Phase Tray .............................................................2-6

2.1.10 UHF Amplifier Tray .....................................................................2-6

2.1.11 Modulator front panel menus and indicators ..................................2-7

2.1.12 Main AC Input............................................................................2-8

2.1.13 Customer Remote Interface Connections.............................. 2-8

CHAPTER 3 INSTALLATION AND SETUP PROCEDURES

3.1 Site Considerations................................................................................3-1

3.2 Unpacking the Cabinets and Trays...........................................................3-4

3.3 Installing the Cabinets and Trays ............................................................3-4

3.3.1 DM8-R Modulator Installation ........................................................3-5

3.4 Main AC Inputs......................................................................................3-6

3.5 Output Connections...............................................................................3-6

3.6 Setup and Operation Procedures.............................................................3-7

3.6.1 DM8-R Modulator Setup Procedures ...............................................3-8

CHAPTER 4 CIRCUIT DESCRIPTIONS

4.1 UHF Exciter Assembly ............................................................................4-1

4.1.1 Control and Status .......................................................................4-1

4.1.2 Digital Input and Remote Connections............................................4-1

4.1.3 AC Input .....................................................................................4-2

4.2 DM8-R Modulator Tray...........................................................................4-2

4.2.1 DM8 Digital Modulator Board .........................................................4-2

4.2.2 DM8-R Front Panel Board..............................................................4-3

4.3 UHF Exciter Tray ..................................................................................4-3

4.3.1 UHF Filter...................................................................................4-3

4.3.2 UHF Generator Board...................................................................4-4

4.3.3 (Optional) 10-MHz Reference Oscillator Board ................................4-4

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Digital UHF Transmitter Table of Contents

TABLE OF CONTENTS

CHAPTER 4 CIRCUIT DESCRIPTIONS - Continued Section Page

4.3.4 PLL Board...................................................................................4-5

4.3.5 Power Entry Module.....................................................................4-7

4.3.6 IF Phase Corrector Board .............................................................4-7

4.3.7 ALC Board ..................................................................................4-9

4.3.8 Visual/Aural Metering Board .......................................................4-15

4.3.9 UHF Upconverter Board..............................................................4-16

4.3.10 Transmitter Control Board .........................................................4-17

4.3.11 +12V(4A)/-12V(1A) Power Supply Board....................................4-22

4.3.12 5-Section Delay Equalizer Board ................................................4-23

4.4 Variable Phase/Gain Tray ....................................................................4-23

4.4.1 Variable Gain/Phase Board ..........................................................4-23

4.4.2 Metering Board ..........................................................................4-24

4.4.3 Power Entry Module....................................................................4-24

4.4.4 +15V/-12V Power Supply Board ..................................................4-24

4.5 Metering Panel ...................................................................................4-24

4.5.1 Splitter Board ............................................................................4-25

4.5.2 Visual/Aural Metering Board ........................................................4-25

4.5.3 Dual Peak Detectors ...................................................................4-25

4.5.4 Detector Threshold Board............................................................4-26

4.5.5 Power Entry Module....................................................................4-26

4.5.6 +/-12V Power Supply Board........................................................4-26

4.6 AC Distribution Assembly, UHF Exciter..................................................4-27

4.7 2-3kW Amplifier Array.........................................................................4-27

4.8 UHF Amplifier Trays............................................................................4-29

4.8.1 UHF Filter.................................................................................4-29

4.8.2 1-Watt Amplifier Board Assembly................................................4-29

4.8.3 1-Watt Amplifier Board ..............................................................4-30

4.8.4 Single Stage Amplifier Assembly.................................................4-30

4.8.5 Coupler Board...........................................................................4-34

4.8.6 Dual Peak Detector Enclosure.....................................................4-34

4.8.7 Dual Peak Detector Board ..........................................................4-34

4.8.8 4-Way Splitter Assembly............................................................4-35

4.8.9 4-Way Splitter Board .................................................................4-35

4.8.10 Dual Stage Amplifier Assembly...................................................4-35

4.8.11 Amplifier Protection Board .........................................................4-39

4.8.12 Amplifier Control Board.............................................................4-40

4.8.13 Variable Gain/Phase Enclosure...................................................4-42

4.8.14 Variable Gain/Phase Board ........................................................4-42

4.8.15 4-Way Combiner Assembly........................................................4-43

4.9 AC Distribution Assembly, Single Phase Amplifier Array..........................4-44

4.10 AC Distribution Assembly, Three Phase Amplifier Array..........................4-45

4.11 Combiner Reject Load Assembly..........................................................4-45

4.11.1 Combiner Reject Load Board......................................................4-46

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Digital UHF Transmitter Table of Contents

TABLE OF CONTENTS - (continued)

Section Page

CHAPTER 5 DETAILED ALIGNMENT PROCEDURES

5.1 DM8-R Modulator ..................................................................................5-1

5.1.1 DM8-R Modulator Board Configuration .........................................5-1

5.2 UHF Exciter Tray ...................................................................................5-2

5.2.1 Delay Equalization Adjustment......................................................5-3

5.2.2 IF Phase Corrector Adjustment .....................................................5-3

5.2.3 UHF Generator Board...................................................................5-3

5.2.4 10-MHz Reference Generator Board ..............................................5-4

5.2.5 PLL Board...................................................................................5-4

5.3 UHF Amplifier Trays...............................................................................5-4

5.3.1 Variable Gain/Phase Board ...........................................................5-4

5.3.2 1-Watt UHF Amplifier Board .........................................................5-4

5.3.3 UHF Filter...................................................................................5-4

5.3.4 Single Stage Amplifier Assembly...................................................5-4

5.3.5 Coupler Board.............................................................................5-4

5.3.6 Dual Stage Amplifier Assembly .....................................................5-5

5.3.7 4-Way Splitter Assembly..............................................................5-5

5.3.8 Dual Stage Amplifier Assembly .....................................................5-5

5.3.9 4-Way Combiner Assembly...........................................................5-6

5.3.10 Circulator...................................................................................5-6

5.3.11 Dual Peak Detector Board............................................................5-6

5.3.12 Amplifier Protection Board ...........................................................5-6

5.3.13 Amplifier Control Board...............................................................5-6

5.3.14 Switching Power Supply ..............................................................5-6

5.3.15 Calibration of Output and Reflected Power and VSWR Cutback ........5-6

5.4 Phase and Gain Adjustment of the UHF Amplifier Trays in each Array..........5-7

5.5 Calibration of the Side A and Side B Arrays Forward Output Power .............5-7

5.6 Calibration of the Side A and Side B Arrays Reflected Output Power............5-7

5.7 Phase and Gain Adjustment for the entire Amplifier Array..........................5-8

5.8 Calibration of the Forward Output Power Level of the Transmitter...............5-8

5.9 Calibration of the Reflected Output Power Level of the Transmitter .............5-8

5.10 Calibration of the Reject Output Power Level of the Transmitter................5-9

APPENDICES APPENDIX A SAMPLE LOG REPORT SHEET APPENDIX B TYPICAL OPERATIONAL READINGS APPENDIX C ASSEMBLY DRAWINGS AND PARTS LISTS APPENDIX D SUBASSEMBLY DRAWINGS AND PARTS LISTS APPENDIX E DT835A SYSTEM SPECIFICATIONS

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Digital UHF Transmitter Table of Contents

LIST OF FIGURES

2-1 Exciter Remote Interface Assembly ................................................2-10

2-2 Amplifier Array Remote Interface Panel ..........................................2-14

3-1 1 kW Minimum Ventilation Configuration...........................................3-4

3-2 Tray Installation Instructions...........................................................3-6

5-1 Typical Digital Spectrum ...............................................................5-12

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Digital UHF Transmitter Table of Contents

LIST OF TABLES

2-1 DT835A Major Assemblies ...............................................................2-1

2-2 Metering Panel Meters.....................................................................2-4

2-3 UHF Exciter Tray Meters..................................................................2-5

2-4 UHF Exciter Tray Switches...............................................................2-5

2-5 UHF Exciter Tray Fault Indicators .....................................................2-5

2-6 UHF Exciter Tray Samples ...............................................................2-6

2-7 Variable Phase/Gain Tray Meters......................................................2-6

2-8 Variable Phase/Gain Tray Sample.....................................................2-6

2-9 UHF Amplifier Tray Meters...............................................................2-6

2-10 UHF Amplifier Tray Status Indicators ................................................2-7

2-11 UHF Amplifier Tray Control Adjustments ...........................................2-7

2-12 UHF Amplifier Tray Sample..............................................................2-7

2-13 Modulator Front Panel LEDs.............................................................2-8

2-14 Customer Remote Control Interface Connections.................... 2-12

3-1 MPEG and 10 MHz Input Information................................................3-6

3-2 Jumper Positions in the Gain 1 and Gain 2 Circuits

For an Input Level of Between –6 and –26 dBm.................................3-8

4-1 Fuses, Idling Currents and Voltage Settings for Amplifier Devices......4-42

5-1 8-VSB Modulator Connections..........................................................5-1

5-2 Jumper Configurations for the Symbol Generator Board......................5-3

5-3 Jumper Configurations for the VSB Filter Board .................................5-5

5-4 DIP Switch Settings........................................................................5-6

5-5 Jumper Positions on the 6 dB Pad ..................................................5-10

5-6 Center Frequencies for the Delay Equalizer Sections.........................5-11

5-7 PLL Board Switch Positions............................................................5-13

5-8 Switch Positions for Channel Frequencies........................................5-14

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Digital UHF Transmitter Chapter 1, Introduction

Chapter 1

Introduction

This manual explains the installation, setup, alignment, and maintenance procedures for the DT835A Digital UHF Transmitter. It is important that you read all of the instructions, especially the safety information in this chapter, before you begin to install or operate the unit.

1.1 Manual Overview This instruction manual is divided into

four chapters and supporting appendices. Chapter 1, Introduction, contains information on safety, maintenance, return procedures, and warranties. The Chapter 2, System Description and Customer Remote Interface Connections, describes the transmitter and includes discussions of system control and status indicators and remote control connections. Chapter 3, Installation and Set up Procedures, explains how to unpack, install, setup, and operate the transmitter. Chapter 4, Circuit Descriptions, provides information on the boards and subassemblies that make up the DT835A. Chapter 5, Detailed Alignment Procedures, provides information on adjusting the system assemblies for optimal operation The appendices contain sample log sheets, typical operational readings, assembly and subassembly drawings and parts list, and system specifications.

1.2 Safety

The digital UHF transmitters manufactured by Axcera are designed for ease of use and repair while providing protection from electrical and mechanical hazards. Listed throughout the manual are notes, cautions, and warnings concerning possible safety hazards that may be encountered while operating or servicing the transmitter. Please review these warnings and familiarize yourself with the operation and servicing

procedures before working on the transmitter.

Read All Instructions – All of the operating and safety instructions should be read and understood before operating this equipment.

Retain Manuals – The manuals for the transmitter should be retained at the transmitter site for future reference. We provide two sets of manuals for this purpose; one set can be left at the office while one set can be kept at the site.

Heed Notes, Warnings, and Cautions – All of the notes, warnings,

and cautions listed in this safety section and throughout the manual must be followed.

Follow Instructions – All of the operating and use instructions for the transmitter should be followed.

Cleaning – Unplug or otherwise disconnect power from the equipment before cleaning. Do not use liquid or aerosol cleaners. Use a damp cloth for cleaning.

Ventilation – Openings in the cabinets and tray front panels are provided for ventilation. To ensure reliable operation, and to protect the unit from overheating, these openings must not be blocked.

Servicing – Do not attempt to service this product yourself until becoming familiar with the equipment. If in doubt, refer all servicing questions to qualified Axcera service personnel.

Replacement Parts – When replacement parts are used, be sure that the parts have the same functional and performance characteristics as the original part. Unauthorized substitutions may result in fire, electric shock, or other

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Digital UHF Transmitter Chapter 1, Introduction

hazards. Please contact the Axcera Technical Service Department if you have any questions regarding service or replacement parts.

1.3 Maintenance

The DT835A is designed with components that require little or no periodic maintenance except for the routine cleaning of the fans and the front panels of the trays.

The amount of time between cleanings depends on the conditions within the transmitter room. While the electronics have been designed to function even if covered with dust, a heavy buildup of dust, dirt, or insects will affect the cooling of the components. This could lead to a thermal shutdown or premature failure of the affected trays.

When the front panels of the trays become dust covered, the top covers should be removed and any accumulated foreign material removed. A vacuum cleaner, utilizing a small wand-type attachment, is an excellent way to suction out the dirt. Alcohol and other cleaning agents should not be used unless you are certain that the solvents will not damage components or the silkscreened markings on the trays and boards. Water-based cleaners can be used, but do not saturate the components. The fans and heatsinks should be cleaned of all dust or dirt to permit the free flow of air for cooling purposes.

It is recommended that the operating parameters of the transmitter be recorded from the meters on the trays and the system metering control panel at least once a month. It is suggested that this data be retained in a rugged folder or envelope. A sample format for a log sheet is provided in Appendix A. Photocopies of the log sheet should be made for continued data entries.

1.4 Material Return Procedure

To insure the efficient handling of equipment or components that have been returned for repair, Axcera requests that each returned item be accompanied by a Material Return Authorization Number (MRA#).

An MRA# can be obtained from any Axcera Field Service Engineer by calling the Axcera Field Service Department, at (724) 873-8100. This procedure applies to all items sent to the Field Service Department regardless of whether the item was originally manufactured by Axcera.

When equipment is sent to the field on loan, an MRA# is included with the unit. The MRA# is intended to be used for the return of the unit to Axcera. In addition, all shipping material should be retained for the return of the unit to Axcera. Replacement assemblies are also sent with an MRA# to allow for the proper routing of the exchanged hardware. Failure to close out this type of MRA# will normally result in invoicing for the value of the loaner item or the exchange assembly.

When shipping an item to Axcera, please include the MRA# on the packing list and on the shipping container. The packing slip should also include contact information and a brief description of why the unit is being returned.

Please forward all MRA items to:

Axcera 103 Freedom Drive P.O. Box 525 Lawrence, PA 15055-0525 USA

For more information concerning this procedure, call the Axcera Field Service Department, at (724) 873-8100 or by fax at (724) 873-8105.

Axcera can also be contacted through email at service@axcera.com and on the Web at www.axcera.com.

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Digital UHF Transmitter Chapter 1, Introduction

1.5 Limited One-Year Warranty for Axcera Products

Axcera warrants each new product that it has manufactured and sold against defects in material and workmanship under normal use and service for a period of one (1) year from the date of shipment from Axcera's plant, when operated in accordance with Axcera's operating instructions. This warranty shall not apply to tubes, fuses, batteries, or bulbs.

Warranties are valid only when and if (a) Axcera receives prompt written notice of breach within the period of warranty, (b) the defective product is properly packed and returned by the buyer (transportation and insurance prepaid), and (c) Axcera determines, in its sole judgment, that the product is defective and not subject to any misuse, neglect, improper installation, negligence, accident, or (unless authorized in writing by Axcera) repair or alteration. Axcera’s exclusive liability for any personal and/or property

damage (including direct, consequential, or incidental) caused by the breach of any or all warranties, shall be limited to the following: (a) repairing or replacing (in Axcera’s sole discretion) any defective parts free of charge (F.O.B. Axcera’s plant) and/or (b) crediting (in Axcera’s sole discretion) all or a portion of the purchase price to the buyer.

Equipment furnished by Axcera, but not bearing its trade name, shall bear no warranties other than the special hoursof-use or other warranties extended by or enforceable against the manufacturer at the time of delivery to the buyer.

NO WARRANTIES, WHETHER STATUTORY, EXPRESSED, OR IMPLIED, AND NO WARRANTIES OF MERCHANTABILITY, FITNESS FOR ANY PARTICULAR PURPOSE, OR FREEDOM FROM INFRINGEMENT, OR THE LIKE, OTHER THAN AS SPECIFIED IN PATENT LIABILITY ARTICLES, AND IN THIS ARTICLE, SHALL APPLY TO THE EQUIPMENT FURNISHED HEREUNDER.

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Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections

Chapter 2

System Description and Customer Remote Connections

MAJOR ASSEMBLY NUMBER TRAY/ASSEMBLY NAME

A1 Single UHF exciter assembly

A2 and A3 two 2-3kW amplifier array assemblies

A4 Hybrid combiner assembly A7 Directional coupler assembly

Output coupler assembly DM8-R digital modulator tray

Table 2-1: DT835A Major Assemblies

2.1 System Overview

The DT835A is a complete UHF solidstate television transmitter that operates at an output power of 2000 watts to 3000 watts digital, depending on the digital application. The DT835A is made up of three cabinets: a UHF exciter cabinet and two amplifier array cabinets.

The DT835A is made up of the trays and assemblies shown in Table 2-1.

2.1.1 (A1) Single UHF Exciter Assembly

The single UHF exciter assembly contains (A1) a UHF exciter tray, a DM8R digital modulator tray, (A10) an (Optional) 10 MHz reference generator tray, (A3) a splitter, (A4 and A5) two variable phase/gain trays, (A6) a metering panel, (A8) an AC distribution assembly, and (A9) a remote interface assembly.

The DM8-R modulator tray can have an external 10 MHz reference connected to J3 on the rear panel or it will generate and internal 10 MHz reference if no external reference is supplied. The Digital input connects to J2 on the remote interface assembly that is cabled to J2 on the DM8-R modulator. The Output from the DM8-R modulator at J4 connects to J6 on the rear of the UHF exciter tray. The Digital IF is wired to J18 on the 5 section delay equalizer board, 44 MHz (1072090). The

processed digital IF signal is then cabled to the J32 on the ALC board (1265-

1305). The digital IF input must be selected as the input. This is accomplished by connecting the jumper W11 on J29 between pins 2 and 3 on the ALC board. The digital IF is wired through the K3 and K4 relays to the rest of the ALC board. The LED DS5, digital IF modulator enable, should be lit. The ALC board has the capability of switching between two different IF inputs, but in this case only the digital IF input is used.

The output of the ALC board (-10 dBm) connects to (A11) the UHF upconverter board (1265-1310) in the upconverter section of the UHF digital exciter. The upconverter takes the LO and heterodynes it with the IF; the signal is then filtered to produce the RF onchannel output.

The (A15-A1) UHF generator board (1565-1109) is mounted in the UHF Generator Enclosure (1519-1144) for EMI and RFI protection. The board contains a VCXO circuit and additional circuitry to multiply the VCXO frequency by eight. The output is split and provides an input to the x8 multiplier circuitry as well as a sample for the PLL board. The amplified eighth harmonic is then fed to the SMA output jack of the board at J3. Typical output level of the signal is +16 dBm nominal.

The (Optional) (A14-A1) 10-MHz reference generator board (1519-1126)

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Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections

is located in the (Optional) (A10) 10-MHz reference kit (1286-1108). The board contains a high-stability crystal oscillator that provides a 10-MHz output that is used as reference frequency for the transmitter. The board is mounted within an enclosed assembly that helps to maintain the operating temperature of the oscillator board.

The (A13) PLL board (1286-1104) is part of the phase lock loop (PLL) circuit, which provides the automatic frequency control (AFC) voltage, that connects to the VCXO assembly, on the UHF Generator board, and maintains the accurate output frequency of the VCXO. The AFC is generated by comparing a sample of the 10-MHz reference to a sample of the VCXO frequency. The PLL board uses an external 10-MHz signal as the reference unless it is missing, then an internally generated 10-MHz signal is used. A sample of the signal from the UHF generator board connects to SMA jack J9, the sample input on the board. The signal is amplified by U8 and coupled to U9, a divide by 20/21 IC. A sample of the signal at the output of U8 is connected to J10, the sample output jack on the board, which is typically connected to the front panel of the tray.

The selected 10-MHz reference connects to amplifier IC U1 whose output is split. A sample of the 10-MHz reference is cabled to jack J3, the 10-MHz output jack, which is connected to J5 on the rear of the tray.

If the 50 kHz from the 10-MHz reference and the 50-kHz from the UHF generator board become unlocked, the red Unlock LED, lights and the Lock LED, located on the LED display board, is extinguished.

The RF output of the UHF exciter at J15 is split two ways by the (A3) splitter. The RF output #1 connects to the input of (A4) one of the variable phase/gain trays and the RF output #2 connects to the input of (A5) the other variable phase/gain tray. The output of the (A4)

variable phase/gain tray connects to (A2) the side A amplifier array assembly. The output of the (A5) variable phase/gain tray connects to (A3) the side B amplifier array assembly.

2.1.2 (Optional) 10 MHz Reference Distribution Amplifier Tray

The (Optional) 10 MHz reference distribution amplifier tray provides a 10 MHz reference at a suitable output level for distribution.

The system is made up of an internal 10 MHz reference source, a reference distribution amplifier, and splitter kit(s) without precise offset IF to distribute the reference signal to each transmitter. The reference distribution amplifier tray utilizes an internal 10 MHz reference generator assembly to generate a 10 MHz reference signal. This signal is then divided into five equivalent signals and then amplified and delivered to the output of the tray.

2.1.3 DM8-R Digital Modulator Tray

The DM8-R modulator Tray is an ATSC compliant 8 VSB modulator that mounts in a standard 19” rack. The DM8-R modulator accepts a SMPTE-310 MPEG data stream and outputs a 6 MHz wide IF output centered at 44 MHz with a pilot carrier at 46.69 MHz. The DM8-R modulator provides linear and nonlinear correction capability for the transmission path as well as internal test sources that are used during initial transmitter installation. All of the functions of the DM8-R modulator are controlled from the LX Controller LCD display and pushbuttons.

2.1.4 Amplifier Array Assemblies

The amplifier array assemblies each contain (A9-A1) an 8-way splitter (ZFSC-8-43) with four to six connections used depending on the power level of the transmitter, four to six (A1, A2, A3,

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Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections

A4, A5 & A6) UHF amplifier trays, (A7) a 4 to 6-way combiner, (A8) an output coupler, (A10) an AC distribution assembly, and (A11) an interface panel.

The RF input from the variable phase/gain tray connects to J1 on (A11) the interface panel in the amplifier array assembly. The RF is connected to the COM input of the 8-way splitter, which splits it eight ways, with six of the outputs connected to J1, the RF input on each of the UHF amplifier trays and the other two outputs terminated with 50Ω. The UHF amplifier trays amplify the RF signals to the power needed to produce a maximum of 300 watts 64 QAM or 8VSB digital per tray.

The outputs of the four, five or six UHF amplifier trays are combined in the 4, 5 or 6-way combiner. This provides approximately half of the power needed to generate the full 8-VSB digital output of the transmitter. The RF output is connected to the output coupler assembly. The output coupler assembly supplies a forward and a reflected power sample of the output from the amplifier assembly to the metering panel in the single exciter assembly.

In each UHF amplifier tray, the forward power and reflected power samples from the 4-way combiner board are connected to the dual peak detector board, single supply, that provides peak detected samples to the amplifier control board. The amplifier control board then supplies DC voltages to the front panel meter of the UHF amplifier tray. Before exiting each UHF amplifier tray, the RF is fed through a circulator for the protection of the tray from high VSWR conditions.

2.1.5 Transmitter Output Assemblies

The outputs of the amplifier array assemblies connect through (A5 and A6) 1-5/8” to 3-1/8” adapters to (A4) a hybrid combiner (55223A) that

combines the output from the amplifier assemblies into a single output. The reject output of the hybrid combiner is connected to (A7) an output coupler that provides a reject sample from J3 to the metering panel in the single UHF exciter assembly for monitoring purposes. The output of the (A7) directional coupler connects to (A8) a 2500-watt reject load that dissipates any reject power produced during the combining process. A (A8-A1) thermal switch is mounted on the 2500-watt reject load that connects to the overtemperature fault circuit on the transmitter control board in the UHF exciter tray. This fault circuit shuts down the transmitter if an overtemperature fault occurs. The overtemperature is normally caused by a large reject power being dissipated by the reject load due to the malfunctioning of one of the amplifier arrays.

The output of the (A4) hybrid combiner at J3 is fed to (A11) the output coupler assembly. The filtered signal is connected to (A11) an output coupler assembly that provides combined forward and reflected power samples to the metering panel in the single UHF exciter assembly. The forward sample is processed to provide peak detected visual and aural power output samples to the front panel meter on the metering panel. The reflected power sample is also peak detected and wired to the front panel meter.

2.1.6 Control and Status

Information on the control and status of the transmitter is provided by the indicators on the metering panel and the variable phase/gain trays. There are also control, status, and LED indicators on the front panel of the UHF exciter tray. The functions of these control and status indicators are shown in the following tables. The switches and LED indicators, which are mounted so that the switches and LEDs can be operated or viewed from the front panel of the UHF exciter, are part of the transmitter control board.

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Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections

On the UHF exciter tray, switch (S1) is an Operate/Standby switch that provides the Operate command (Enable), when in Operate, to the each of the amplifier arrays. The Enable to each amplifier array is split four, five or six ways and then applied to the UHF amplifier trays. The Enable is needed to turn on the switching power supplies located in the UHF amplifier trays.

When the UHF exciter is in Operate, the green LED (DS2) is on and when the exciter is in Standby, the amber LED (DS1) is on.

NOTE: If the transmitter does not switch to Operate when S1 is switched to Operate, check that a dummy jumper

plug, with a jumper between pins 1 and 2, is connected to jack J7 on (A9) the remote interface assembly in the single UHF exciter assembly. This jumper provides the interlock needed for the operation of the transmitter. If the interlock is present, the green LED (DS5) on the transmitter control board should be lit.

The operation of the transmitter is controlled by the front panel switches on the UHF exciter tray. During normal operation of the transmitter, switch S2 should be in the Auto position. The front panel of the UHF exciter also has LEDs that indicate a Modulation Fault (Loss), red LED (DS9), and a VSWR Cutback, amber LED (DS7).

2.1.7 Metering Panel

Table 2-2: Metering Panel Meters

METER FUNCTION Combination meter (A13)

Displays power in terms of a percentage of the calibrated transmitter output level on the scale; a full-scale reading is 120%

Switch (S1), meter Selects the desired % Forward, % Reject, or % Reflected

reading. % Forward (0 - 120 %) Displays the output power level (≈100%) % Reject (0 - 120 %) Displays the % Reject Output Power (<5%) % Reflected (0 - 120 %) Displays the % Reflected Output Power (<5%)

Power meter side A (A15)

Displays power in terms of a percentage of the calibrated

amplifier array output level on the scale; a full-scale reading

is 120% Switch (S2), meter Selects the desired % Forward or % Reflected reading Forward (0 - 120 %) Displays the output level of the array (≈ 95%) % Reflected (0 - 120 %) Displays the % Reflected Output Power of the array (<5%)

Power meter side B (A16)

Displays power in terms of a percentage of the calibrated

amplifier array output level on the scale; a full-scale reading

is 120% Switch (S3), meter Selects the desired % Forward or % Reflected reading Forward (0 - 120 %) Displays the output level of the array (≈ 95%) % Reflected (0 - 120 %) Displays the % Reflected Output Power of the array (< 5%)

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2.1.8 UHF Exciter Tray

Table 2-3: UHF Exciter Tray Meters

METER FUNCTION

Meter (A18) Displays power in terms of a percentage of the calibrated

exciter output level on the upper scale. The voltage level is read on one of the two bottom scales. A full-scale reading on the top scale is 120%. 100% equals +10 dBm 8-VSB digital.

Also reads the ALC voltage level. Switch (S3), meter Selects the desired % Exciter or the ALC voltage reading ALC (0 - 1 V) Displays the ALC voltage level (≈0.85 VDC) % Exciter Displays the % Exciter Output Power. This is the level needed

to attain (0 -100) which is the desired output power of the

transmitter (≈ 30 %).

Table 2-4: UHF Exciter Tray Switches

SWITCH FUNCTION

Transmitter (S1) Operate/Standby

Mode Select (S2) Auto/Manual

FAULT INDICATOR FUNCTION Modulation loss (DS9 red) VSWR cutback (DS7 amber)

The momentary contact switch (S1) applies a ground to K1, a latching relay, on the transmitter control board. K1 will switch either to Operate or to Standby depending on which direction S1 is pushed. When switched to Operate, a low, Enable command, is applied to the UHF amplifier trays mounted in the amplifier arrays. These Enables will turn on the UHF amplifier trays. The opposite occurs when the transmitter is switched to Standby. The momentary contact switch (S2) applies a ground to K2, a latching relay, on the transmitter control board. K2 will switch the transmitter to Automatic or Manual depending on which direction S2 is pushed. In Automatic, the Modulation Fault command from the ALC board will control the operation of the transmitter. The transmitter will switch to Standby, after a slight delay, if the input modulation is lost and will quickly switch back to Operate when the modulation is restored. In Manual, the transmitter is controlled by the operator using the front panel Operate/Standby switch or by remote control.

Table 2-5: UHF Exciter Tray Fault Indicators

Indicates that the input has been lost to the transmitter. The fault is generated on the ALC board in the UHF exciter tray. Indicates that the reflected power level of the transmitter has increased above 20%. This will automatically cut back the output power level to 20%. The fault is generated on the transmitter control board in the UHF exciter tray.

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Table 2-6: UHF Exciter Tray Samples

SAMPLE DESCRIPTION f(s) A sample of the channel oscillator output taken from

the sample jack of the PLL board

Exciter O/P An output power sample of the exciter taken from the

UHF upconverter board

2.1.9 Variable Phase/Gain Trays

Table 2-7: Variable Phase/Gain Tray Meters

METER FUNCTION

Switch (S1), meter Selects the desired % Power or the ALC voltage

reading

% Output Power Displays the % Output Power of the amplifier array

(100%=+15 dBm 8- VSB digital ≈45%)

ALC Displays the ALC voltage from the UHF exciter that

connects to the amplifier trays in the amplifier array (.6 - 1 VDC typical)

Table 2-8: Variable Phase/Gain Tray Sample

SAMPLE DESCRIPTION

Output (J4), (0 dBm) A front panel sample of the RF output of the

phase/gain tray, which connects to the amplifier array, taken from the variable gain/phase board

2.1.10 UHF Amplifier Trays

Table 2-9: UHF Amplifier Tray Meters

METER FUNCTION

Meter (A9) Displays power in terms of a percent of the calibrated power

output value. A full-scale reading is 100%, which is equivalent to 300 watts 8-VSB digital. Also reads % Reflected Power, power

supply voltage levels, and AGC voltage levels. Switch (S2), meter % Output pwr Displays the % Output Power of the tray (100%=300 watts 8-VSB

% Refl (Reflected) Power supply Displays the power supply voltage, +26.5 VDC, on the middle

AGC voltage Displays the AGC voltage level, +1 - +2 VDC, on the bottom scale

Selects the desired % Power or the voltage reading

digital)

Displays the % Reflected Output Power of the tray (<5% with all

amplifier trays operating as measured on the top scale)

scale

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Table 2-10: UHF Amplifier Tray Status Indicators

INDICATOR FUNCTION

Enable (DS4 green) Indicates that an Enable, Operate command, is

applied to the UHF amplifier tray from the selected UHF exciter tray

Overdrive (DS2 red) Indicates that the level of the drive is too high. The

protection circuit will limit the drive to the set threshold. The fault is generated on the amplifier control board.

VSWR cutback (DS1 red) Indicates that the reflected power level of the tray has

increased above 50%. This will automatically cut back the output power level to 50%. The fault is generated on the amplifier control board.

Overtemp (DS3 red) Indicates that the temperature of (A5-A6- A3 and A5-

A6-A4), one or both of two thermal switches mounted on the heatsink assembly for the output amplifiers, is above 175° F. When this fault occurs, the Enable to the switching power supply in the affected amplifier tray is immediately removed and it will shut down.

Input fault (DS5 red) Indicates that the input RF level to the amplifier trays

dropped below the 0 dBm range

Table 2-11: UHF Amplifier Tray Control Adjustments

ADJUSTMENT FUNCTION

Phase (A10-R5) Adjusts the phase of the RF output by approximately

70°

Gain (A11-R6) Adjusts the gain of the RF output when the amplifier

control board is in the AGC mode

Table 2-12: UHF Amplifier Tray Sample

SAMPLE DESCRIPTION

Module O/P (0 dBm) A sample of the combined output of the four dual-

stage amplifier boards taken from the dual-peak detector board

2.1.11 DM8-R Modulator Front Panel LED Indicators

The front panel LEDs are described in Table 2-13.

Table 2-13: Modulator Front Panel LEDs

LED Indicator Function

PWR Indicates that the DC power supply is operating

MPEG

LED

PLL A

LED

PLL B

LED

Indicates the presence of a valid MPEG stream at the J1-2B input Indicates that the DM8 symbol clock is locked to the frequency of the 10 MHz reference. Indicates that the pilot frequency is locked to the incoming 10 MHz reference.

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2.1.12 Main AC Input

The transmitter needs an AC input of 208/240 VAC at 100 amps for each amplifier array assembly and at 20 amps for the exciter assembly.

The 208/240 VAC input to each amplifier assembly connects to (A10) the AC distribution assembly, amplifier array (1278-1200), on the right, center of each cabinet. The assembly contains the terminal block (TB1) that connects to the 208/240 VAC. Line 1 is connected to TB1-1A, line 2 to TB1-3A, and safety ground to TB1-4A.

The distribution assembly contains nine circuit breakers that supply the AC to the rest of the amplifier assembly. The input AC from TB1 is connected to (CB1) the main AC circuit breaker (100 amps) that distributes the 208/240 VAC to the other eight circuit breakers. The output of CB1 has three MOVs, VR3, VR4, and VR6, mounted to it: VR4 is connected from line 1 to ground, VR6 is connected from line 2 to ground and VR3 is mounted across the two lines. The switched input AC is wired through the six circuit breakers, CB2-CB7, to the six UHF amplifier trays in the amplifier cabinets. CB2 is a 20-amp circuit breaker that supplies the AC voltage to the (A1) UHF amplifier tray. CB3 is a 20amp circuit breaker that supplies the AC voltage to the (A2) UHF amplifier tray. CB4 is a 20-amp circuit breaker that supplies the AC voltage to the (A3) UHF amplifier tray. CB5 is a 20-amp circuit breaker that supplies the AC voltage to the (A4) UHF amplifier tray. CB6 is a 20amp circuit breaker that supplies the AC voltage to the (A5) UHF amplifier tray. CB7 is a 20-amp circuit breaker that supplies the AC voltage to the (A6) UHF amplifier tray. The circuit breakers CB8 and CB9 control the AC to the A12-A3 and A12-A5 fans mounted on the (optional) (A12) reject load assembly

that only used as part of the 2.5 and 3 kW amplifier array assemblies.

The 208/240 VAC input to the single UHF exciter assembly connects to (A8) the AC distribution assembly, single UHF exciter assembly (1245-1500), in the right, center rear of the cabinet. The assembly contains the terminal block (TB1) that connects to the 208/240 VAC. Line 1 is connected to TB1-1A, line 2 to TB1-3A, and ground to TB1-2A. The AC distribution panel contains (CB1) the main circuit breaker (20 amps) that supplies the AC to the rest of the single exciter assembly. The output of CB1 has three MOVs, VR1, VR2, and VR3, connected to it: VR1 from line 1 to ground, VR3 from Line 2 to ground and VR2 across the two lines. The AC output of CB1 connects to A1 and A2, the IEC outlet strips, into which the external trays connect. The (A1) UHF exciter tray and the (A4) variable phase/gain tray plug into the (A1) IEC outlet strip. The (A5) variable phase/gain tray, the (A6) metering panel, the (optional) (A7) receiver tray, the 8 VSB modulator tray or other optional trays plug into the (A2) IEC outlet strip. When the circuit breaker CB1 on the single UHF exciter assembly is switched on, +12 VDC from the UHF exciter tray is supplied to each of the amplifier array cabinets. The +12 VDC is split six ways in the amplifier array and connected to each of the UHF amplifier trays to operate the LED status indicators in the tray. Also +12V is connected to the (Optional) external exhaust kit, if present.

2.1.13 Customer Remote Interface Connections

The remote monitoring and operation of the transmitter is provided through the jacks (J8, J9, and J10) on (A9) the remote interface assembly mounted on the rear of the single UHF exciter assembly (see Figure 2-1).

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Figure 2-1: Exciter Remote Interface Assembly

Jack (J7) should have a dummy plug connected to it, with a jumper connected between pins 1 and 2, to provide the interlock to the exciter needed to operate the transmitter. If the jumper is missing, the transmitter will not switch to Operate. If remote connections are made to the

through the plugs provided in the installation material for the transmitter and wired as indicated on the interconnect drawing for the single UHF exciter assembly (11056919). The remote control interface connections for this transmitter are shown in Table 2-14.

transmitter, they should be made

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Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections

Table 2-14: Remote Control Interface Connections

FUNCTION

Exciter Enable Interlock J7-1 Exciter Enable Interlock Rtn J7-2

Transmitter Remote Metering

Combined Output Power J10-7 Combined Output Power Rtn J10-8

Combined Reflected Power J10-9 Combined Reflected Power Rtn

Exciter Output J9-26 Exciter Output Rtn J9-27

Exciter Remote Control Commands

Exciter Operate (Enable) J8-3 Contact closure Exciter Standby/Operate Rtn J8-2 Exciter Standby (Disable) J8-1 Contact closure

Exciter Auto J8-6 Contact closure Exciter Auto/Manual Rtn J8-5 Exciter Manual J8-4 Contact closure

Power Raise (optional) J9-6 Contact closure Raise/Lower Rtn (optional) J9-5 Power Lower (optional) J9-4 Contact closure

Exc Modulator Select (optional) Exc Modulator Select Rtn (optional)

Exciter Remote Status Indications

Exciter Auto Mode Indicator J9-30 50 mA max current sink Auto/Manual Mode Ind Rtn J9-31 Exciter Manual Mode Indicator

Operate Indicator J9-1 50 mA max current sink Operate/Standby Ind Rtn J9-2 Standby Indicator J9-3 50 mA max current sink

REMOTE JACK/PIN

NUMBER

J10-10

J8-10 Contact closure

J8-11

J9-32 50 mA max current sink

INTERFACE TYPE

J7-1 and 2 must be jumpered together for normal operation.

1V full scale at 1kΩ source resistance

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Digital UHF Transmitter Chapter 2, System Description and Customer Remote Connections

FUNCTION

Exciter VSWR Cutback Indicator

Video Loss Indicator J9-7 50 mA max current sink Video Loss Indicator Rtn J9-8

Exc Receiver Fault Ind (optional)

Side A Driver Remote Metering

Side A Driver Output Power J10-1 Side A Driver Output Power Rtn

Side B Driver Remote Metering

Side B Driver Output Power J10-3 Side B Driver Output Power Rtn

Side A Forward Power J10-14 Side A Forward Power Rtn J10-15

Side A Reflected Power J10-16 Side A Reflected Power Rtn J10-17

Side B Forward Power J10-20 Side B Forward Power Rtn J10-21

Side B Reflected Power J10-18 Side B Reflected Power Rtn J10-19

Side A + B Remote Metering

Reject Power J10-11 Reject Power Rtn J10-12 The above connections are made to jack (J9), the 37-position “D” connector; to jack (J10), the 25-position “D” connector; to jack (J8), the 25-position “D” connector; or to jack (J7), the 9-position “D” connector on (A9) the remote interface assembly mounted at the top, rear of the single UHF exciter cabinet.

REMOTE JACK/PIN

NUMBER

J8-7 50 mA max current sink

J8-9 50 mA max current sink

J10-2

J10-4

Side A Remote Metering

Side B Remote Metering

INTERFACE TYPE

1V full scale at 1kΩ source resistance

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Figure 2-2: Amplifier Array Remote Interface Panel

Amplifier Array Assembly Remote Metering

(A1) UHF Amp Tray Refl Pwr J5-2 (A1) Reflected Power Rtn J5-1

(A1) UHF Amp Tray Fwrd Pwr J5-4 (A1) Forward Power Rtn J5-3

(A2) UHF Amp Tray Refl Pwr J5-6 (A2) Reflected Power Rtn J5-5

(A2) UHF Amp Tray Fwrd Pwr J5-8 (A2) Forward Power Rtn J5-7

(A3) UHF Amp Tray Refl Pwr J5-9 (A3) Reflected Power Rtn J5-10

(A3) UHF Amp Tray Fwrd Pwr J5-11 (A3) Forward Power Rtn J5-12

(A4) UHF Amp Tray Fwrd Pwr J5-13 (A4) Forward Power Rtn J5-14

(A4) UHF Amp Tray Refl Pwr J5-15 (A4) Reflected Power Rtn J5-16

(A5) UHF Amp Tray Fwrd Pwr J5-18 (A5) Forward Power Rtn J5-17

(A5) UHF Amp Tray Refl Pwr J5-21 (A5) Reflected Power Rtn J5-20

The above connections are made to jack (J5), the 37-position “D” connector on (A11) the remote interface panel (Figure 2-2) mounted at the top, rear of each of the amplifier array cabinets.

1V full scale at 1kΩ source resistance

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Digital UHF Transmitter Chapter 3, Installation and Setup Procedures

Chapter 3

Installation and Setup Procedures

There are special considerations that need to be taken into account before the DT835A can be installed. For example, if the installation is completed during cool weather, a heat-related problem may not surface for many months, suddenly appearing during the heat of summer. This section provides planning information for the installation and set up of the transmitter.

3.1 Site Considerations

The transmitter requires an AC input line of 220 VAC with a rating of 20 amps for the exciter cabinet and 100 amps for each amplifier cabinet. Make sure that the proposed site for the transmitter has the voltage requirements that are needed.

The DT835A is designed and built to provide long life with a minimum of maintenance. The environment in which it is placed is important and certain precautions must be taken. The three greatest dangers to the transmitter are heat, dirt, and moisture. Heat is usually the greatest problem, followed by dirt, and then moisture. Over-temperature can cause heat-related problems such as thermal runaway and component failure. Each amplifier tray in the transmitter contains a thermal interlock protection circuit that will shut down that tray until the temperature drops to an acceptable level.

A suitable environment for the transmitter can enhance the overall performance and reliability of the transmitter and maximize revenues by minimizing down time. A properly designed facility will have an adequate supply of cool, clean air, free of airborne particulates of any kind, and no excessive humidity. An ideal environment will require temperature in the range of 40° F to 70° F throughout the year,

reasonably low humidity, and a dust-free room. It should be noted that this is rarely if ever attainable in the real world. However, the closer the environment is to this design, the greater the operating capacity of the transmitter.

The fans and blowers designed and built into the transmitter will remove the heat from within the trays, but additional means are required for removing this heat from the building. To achieve this, a few considerations should be taken into account. The first step is to determine the amount of heat to be removed. There are generally three sources of heat that must be considered. The first and most obvious is the heat from the transmitter itself. This can be determined by subtracting the average power to the antenna (1500 watts) from the AC input power (15,000 watts). This number in watts (13,500) is then multiplied by

3.41, which gives 46,035, the BTUs to be removed every hour. 12,000 BTUs per hour equals one ton, so a 4-ton air conditioner will cool a 1.5 kW digital transmitter.

The second source of heat is other equipment in the same room. This number is calculated in the same way as the equation for BTUs. The third source of heat is equally obvious but not as simple to calculate. This is the heat coming through the walls, roof, and windows on a hot summer day. Unless the underside is exposed, the floor is usually not a problem. Determining this number is usually best left up to a qualified HVAC technician. There are far too many variables to even estimate this number without detailed drawings of the site showing all construction details. The sum of these three sources is the total amount of heat that must be removed. There may be other sources of heat, such as personnel, and all should be taken into account.

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Now that the amount of heat that must be removed is known, the next step is to determine how to accomplish this. The options are air conditioning, ventilation, or a combination of the two. Air conditioning is always the preferred method and is the only way to create anything close to an ideal environment.

Ventilation will work quite well if the ambient air temperature is below 100° F, or about 38° C, and the humidity is be kept at a reasonable level. In addition, the air stream must be adequately filtered to ensure that no airborne particulate of any kind will be carried into the transmitter. The combination of air conditioning for summer and ventilation during the cooler months is acceptable when the proper cooling cannot be obtained through the use of ventilation alone and using air conditioning throughout the year is not feasible.

Caution: The operation of air conditioning and ventilation simultaneously is not recommended. This can cause condensation in transmitters. For tube type transmitters, this can be especially serious if the condensation forms in the tube cavity and creates damaging arcs.

The following precautions should be observed regarding air conditioning systems:

1. Air conditioners have an ARI

nominal cooling capacity rating. In selecting an air conditioner, do not assume that this number can be equated to the requirements of the site. Make certain that the contractor uses the actual conditions that are to be maintained at the site in determining the size of the air conditioning unit. With the desired conditioned room temperature under 80° F, the unit must be derated, possibly by a substantial amount.

2. Do not have the air conditioner blowing directly onto the transmitter. Condensation may occur on, or worse in, the transmitter under certain conditions.

3. Do not isolate the front of the transmitter from the back with the thought of air conditioning only the front of the unit. Cooling air is drawn in at the front of all transmitters and in the front and back of others. Any attempt to isolate the front from the rear will adversely affect the cooling air flow.

4. Interlocking the transmitter with the air conditioner is recommended to keep the transmitter from operating without the necessary cooling.

5. The periodic cleaning of all filters is a must.

When using ventilation alone, the following general statements apply:

1. The blower, with attendant filters, should be on the inlet, thereby pressurizing the room and preventing dirt from entering the transmitter.

2. The inlet and outlet vents should be on the same side of the building, preferably the leeward side. As a result, the pressure differential created by wind will be minimized. Only the outlet vent may be released through the roof.

3. The inlet and outlet vents should be screened with 1/8" hardware cloth (preferred) or galvanized hardware cloth (acceptable).

4. Cooling air should enter the room as low as practical but in no case higher than four feet above the floor. The inlet must be located

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where dirt, leaves or snow will not be carried in with the cooling air.

5. The exhaust should be located as high as possible. Some ducting is usually required to insure the complete flushing of heated air with no stagnant areas.

6. The filter area must be adequate to insure a maximum air velocity of 300 feet per minute through the filter. This is not a conservative number but a never-exceed number. In a dusty or remote location, this number should be reduced to 150 CFM.

7. The inlet and outlet(s) must have automatic dampers that close any time the ventilation blower is off.

8. In those cases in which transmitters are regularly off for a portion of each day, a temperature-differential sensor that controls a small heater must be installed. This sensor will monitor inside and outside temperatures simultaneously. If the inside temperature falls to within 5° F of the outside temperature, the heater will come on. This will prevent condensation when the ventilation blower comes on and applies even in the summer.

9. A controlled-air bypass system must be installed to prevent the temperature in the room from falling below 40° F during transmitter operation.

10. The blower should have two speeds, which are thermostatically controlled, and interlocked with the transmitter.

11. The blower on high speed must be capable of moving the required volume of air into a half inch of water pressure at the required

elevation. The free air delivery method must not be used.

12. Regular maintenance of any filters can not be overemphasized.

13. Tube transmitters should not rely on the internal blower to exhaust cooling air at elevations above 4000 feet. For external venting, the air vent on the cabinet top must be increased to an 8" diameter for a 1 kW transmitter and to 10" for 5 kW and 10 kW transmitters. An equivalent rectangular duct may be used but, in all cases, the outlet must be increased in area by 50% through the outlet screen.

14. It is recommended that a site plan be submitted to Axcera for comments before installation commences.

In calculating the blower requirements, filter size, and exhaust size, if the total load is known in watts, 2000 CFM into 1/2" of water will be required for each 5000 watts. If the load is known in BTUs, 2000 CFM into 1/2" of water will be required for each 17,000 BTUs. The inlet filter must be a minimum of seven square feet, larger for dusty and remote locations, for each 5000 watts or 17,000 BTUs. The exhaust must be at least four square feet at the exhaust screen for each 5000 watts or 17,000 BTUs.

The information presented in this section is intended to serve only as a general guide and may need to be modified for unusually severe conditions. A combination of air conditioning and ventilation should not be difficult to design (see Figure 3-1). System interlocking and thermostat settings should be reviewed with Axcera. As with any equipment installation, it is always good practice to consult the manufacturer when questions arise. Axcera can be contacted at (724) 873-8100.

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Figure 3-1. 1 kW Minimum Ventilation Configuration

3.2 Unpacking the Cabinets and Trays

Note: Air conditioning and any related heat exhaust ducts should be in place before continuing with the installation of the transmitter.

Thoroughly inspect the cabinets and all other materials upon their arrival. Axcera certifies that upon leaving our facility the equipment was undamaged and in proper working order. The shipping containers should be inspected for obvious damage that indicates rough handling. Check for dents and scratches or broken switches, meters, or connectors. Any claims against in-transit damage should be directed to the carrier. Inform Axcera as to the extent of any damage as soon as possible.

Remove the cabinets, trays, hybrid combiner, bandpass filter, trap filter, and output couplers, along with any installation material, from the crates and boxes. Remove the straps that hold the cabinets to the shipping skids and slide the cabinets from the skids. Remove the plastic wrap and foam protection from

around the cabinets. Do not remove any labeling or tags from any cables or connectors. These are identification markers that make reassembly of the transmitter much easier.

3.3 Installing the Cabinets and Trays

There are three cabinets: (A1) the single UHF exciter assembly, (A2) the side A amplifier array assembly, and (A3) the side B amplifier array assembly. With the operator facing the cabinets, they should be arranged from left to right with the single UHF exciter cabinet on the left, the side A amplifier cabinet in the center, and the side B amplifier cabinet on the right.

The cabinets should be positioned with consideration given to adequate air intake and exhaust, the opening of the rear door, access to the trays (including sliding them out for testing), the AC hookup, and the installation of the output transmission line. The cabinets should be grounded using copper strapping material and should also be permanently mounted to the floor of the site using the holes in the bottom of the cabinets.

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If trays are pre-mounted in the exciter cabinet, remove the two L-brackets, mounted on the front panel rails of the single exciter cabinet, which hold the trays in place during shipment. The UHF amplifier trays are shipped separately from the amplifier array cabinets because of the weight of each tray. The trays are mounted in the cabinet using Chassis Trak cabinet slides. The tray slides are on the top and bottom of the UHF amplifier trays and on the sides of the UHF exciter tray and the variable phase/gain trays. Inspect the trays for any loose hardware or connectors, tightening where needed. Open the rear door; the key to unlock the door, if the door has the optional lock, is found in a tan envelope taped to the door. Inspect the interior for packing material and carefully remove any packing material that is found. Slowly slide each tray in and out to verify that they do not rub against each other and have no restrictions to free movement.

Note: The UHF amplifier trays must be placed into the cabinets in the proper location, and according to the labeling on each tray, or the gain and the phasing will not be maximized.

The UHF amplifier trays are labeled to indicate where they are positioned in the side A or the side B amplifier cabinets. They are mounted in each cabinet from bottom left to top right, with A1 the bottom, left tray and A6 (if used) the top, right tray. Locate the tray labeled A1 and slide it into the side A cabinet in the bottom, left position. Locate the tray labeled A2 and slide it into the side A cabinet in the bottom, right position. Locate the tray labeled A3 and slide it into the side A cabinet in the middle, left position. Locate the tray labeled A4 and slide it into the side A cabinet in the middle, right position. Locate the tray labeled A5 and slide it into the side A cabinet in the top, left position.

Locate the UHF amplifier tray labeled B1 and slide it into the side B cabinet in the bottom, left position. Locate the tray

labeled B2 and slide it into the side B cabinet in the bottom, right position. Locate the tray labeled B3 and slide it into the side B cabinet in the middle, left position. Locate the tray labeled B4 and slide it into the side B cabinet in the middle, right position. Locate the tray labeled B5 and slide it into the side B cabinet in the top, left position. All of the amplifier trays should now be installed. Slowly slide each tray in and out to verify that they do not rub against each other and have no restrictions to free movement.

Caution: Each UHF amplifier tray has a hard-line coaxial cable connected to the rear panel. The tray will not slide out without first removing this connection.

In order to pull out the tray for test purposes or other reasons, use the test cable included in the installation material kit for connections from the tray to the output cable.

It may be necessary to make adjustments to the positions of the trays. This can be accomplished by loosening the cabinet slide mounting bolts that hold the front of the slide to the mounting frame of the cabinet and moving the tray up or down or left or right, as needed, to correct for any misalignment.

3.3.1 DM8-R Modulator Installation

1. If not pre-mounted, remove the

modulator tray from the shipping box and inspect it for any damage that may have occurred during shipment. Remove all packing material used to protect the unit during shipment.

2. The tray mounts using four clearance

holes into a standard 19" rack or cabinet. Mount the tray into the cabinet and adjust or align the tray so that it does not interfere with cabling or other trays.

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3. Verify that the circuit breaker (CB1), located on the rear of the tray, and the main circuit breaker for the system are off.

4. Connect the AC power cord, provided in the installation kit, to J1, the AC input jack on the rear of the tray.

5. Connect the MPEG input to J2, the IF output from J4, and the 10 MHz reference input, if supplied, to J3 on the rear of the tray.

6. Connect the IF output at J4 to the digital IF input to the upconverter of the system.

This completes the installation procedure for the DM8-R modulator.

3.4 Main AC Inputs

Once the cabinets are in place, and the trays have been checked for damage and alignment, the main AC hookup is ready to be made.

Caution: Before connecting the 208/240 VAC, make certain that all of the circuit breakers associated with the transmitter are switched off.

There are three AC input circuits to the DT835A transmitter: one is 20 amps and the two others are 100 amps single phase. The input AC to the exciter cabinet should be a 20 amp, 208/240 VAC line. The input AC to each amplifier cabinet should be a single-phase, 100 amp, 208/240 VAC line.

The 20-amp, 208/240 VAC input connections are made to the terminal block A1-TB1, part of the AC distribution

assembly, exciter cabinet (1245-1500), near the center, right-hand side, rear portion of cabinet #1. Connect terminal 1 to line 1, terminal 3 to line 2 (208/240 VAC), and terminal 2 to the chassis ground.

For single phase - Connect one of the 100-amp, 208/240 VAC inputs to the terminal block A3-TB1, part of the AC distribution assembly, amplifier assembly (1278-1100), near the center, right-hand side, rear portion of cabinet #2. Connect line 1 to TB1-1A, line 2 to TB1-3A and the safety ground to TB14A. Follow the same procedure for cabinet #3.

3.5 Output Connections

The RF output of the (A2) amplifier assembly connects through (A5) a 1-5/8" to 3-1/8" adapter to J1 on (A4) the hybrid combiner. The RF output of the (A3) amplifier assembly connects through (A6) a 1-5/8" to 3-1/8" adapter to J2 on (A4) the hybrid combiner. The reject output of the combiner at J4 connects through (A12) a 1-5/8” to 31/8” adapter to (A7) a directional coupler (1016-1043) and then to (A8) the 2500watt reject load. The combined RF output of the combiner at J3 connects through (A9) the bandpass filter to (A10) the output trap filter assembly. The filtered output connects through (A11) the output coupler assembly (1020-1002) to the transmission line that is connected to the antenna.

This completes the unpacking and installation procedures for the DT835A transmitter. Refer to the setup and operation procedures that follow before applying power to the transmitter.

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Digital UHF Transmitter Chapter 3, Installation and Setup Procedures

Table 3-2: Jumper Positions in the Gain 1 and Gain 2 Circuits for an

Input Level of Between –6 and –26 dBm

IF Input Range W3 on J4 and W4 on J5 W5 on J6 and W6 on J7

-11 to -6 dBm Low Low

-16 to -11 dBm Low High

-21 to -16 dBm High Low

-26 to -21 dBm High High

3.6 Setup and Operation Procedures

The transmitter should initially be turned on with the RF output at J2 of the (A11) output coupler assembly terminated into a dummy load. If a load is not available, check that the output of the coupler assembly at J2 is connected to the antenna. Connect the digital IF input to J6 on the rear of the UHF exciter tray. On (A5) the 5 Section delay equalizer board, 44 MHz, set the input matching jumpers J2 and J3 to positions 1 and 2 for a 50Ω input, or to positions 2 and 3 for a 75Ω input, as needed. Depending on the input level, two gain circuits on the delay equalizer board, 44 MHz, are adjusted using jumpers, W3-W6, to set the gain through the board. Table 3-2 shows the jumper positions in the gain 1 and gain 2 circuits for an input level of between -6 to -26 dBm.

Switch on the main AC circuit breaker on the AC distribution assembly mounted toward the rear of the single UHF exciter assembly. Switch on the main AC circuit breakers on the AC distribution assemblies mounted toward the rear of the amplifier cabinets. Switch on the CB2-CB6 circuit breakers for the individual UHF amplifier trays on the AC distribution assemblies mounted in each amplifier array cabinet.

Switch the Operate/Standby switch on the UHF exciter to standby and the Auto/Manual switch, also on the UHF exciter, to Auto. Normal operation of the transmitter is with the switch in Automatic. Automatic operation of the exciter uses the digital input to the exciter as an Operate/Standby switch. In Auto, if the input is lost, the exciter will

automatically cause the transmitter to revert to Standby. When the input signal is restored, the exciter will automatically return the transmitter to Operate.

Move the Operate/Standby switch on the exciter to Operate. Observe the power supply readings on the front panel meters of the UHF amplifier trays in each amplifier cabinet assembly; the reading should be +26.5 VDC.

Note: If the transmitter does not switch to Operate when the Operate/Standby switch is switched to Operate, check that there is an external interlock plug connected to jack (J7) on the remote interface assembly mounted in the top, rear of the single UHF exciter cabinet. Make sure that the plug has a jumper from pins 1 to 2 to provide the interlock for the exciter. The interlock must be present for the transmitter to operate.

Observe the front panel meter on the metering panel with the switch in the Combined Visual Output Power position; it should read 100%. If needed, adjust the power adjust screwdriver pot on the front panel of the UHF exciter to attain a 100% reading on the front panel meter.

At the same time that the output power is being observed, check the meter readings on the metering panel and the combined meter, in the % Reflected Power position, for the side A and side B amplifier assemblies. If the % Reflected Power for any of the readings is very high, above 50%, a problem is present with the output coaxial lines in the side A amplifier assembly or in the output lines

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Digital UHF Transmitter Chapter 3, Installation and Setup Procedures

for the system and needs to be checked and corrected. A center bullet missing from the 1-5/8" or 3-1/8" rigid coax lines or loose bolts on the connections can cause this problem. Return the Operate/Standby switch to Standby.

Observe the % Exciter Power reading of the meter on the exciter; it should be the same as on the Test Data Sheet for the transmitter, typically 70%. Move the Operate/Standby switch on the exciter to Standby.

The gain and phase controls on the front panels of the individual UHF amplifier trays were adjusted at the factory to attain 100% output of the transmitter and should not need to be readjusted. The forward meter readings for side A and side B may not be the same, but should be the same as the values written on the Test Data Sheet. Side A and side B are combined to give the total output, which is 100% in the combined output power position.

The readings on each of the individual UHF amplifier trays may not be the same. Refer to the Test Data Sheet and compare the final readings from the factory with the readings on each of the trays after the setup. They should be

very similar. If a reading is way off, refer to the phasing and power adjustment procedures for the UHF amplifier trays in Chapter 5, Detailed Alignment Procedures, of this manual before trying to make any adjustments.

If a dummy load is connected to the transmitter, switch the transmitter to Standby and switch off the main AC circuit breakers found on the AC distribution panels in each cabinet. Remove the dummy load and make all of the connections needed to connect the transmitter to the antenna. Switch the main AC circuit breakers on and the Operate/Standby switch to Operate. Adjust the exciter power adjust pot to attain 100% combined visual output.

If the transmitter is already connected to the antenna, check that the combined power output is 100%. If necessary, adjust the power adjust pot located on the UHF exciter for 100%.

3.6.1 DM8-R Modulator Setup Procedures

NOTE: The modulator was setup at the factory to meet specifications for digital mask and corrections and should not need adjusted.

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Digital UHF Transmitter Chapter 4, Circuit Descriptions

Chapter 4

Circuit Descriptions

4.1 (A1) UHF Exciter Assembly

The (A1) UHF Exciter Assembly contains (A1) a UHF Exciter Tray (1142445), (A4 & A5) two Variable Gain/Phase Trays (1245-1200), (A6) a Metering Panel (1061456), (A8) an AC Distribution Assembly, Exciter (1245-

1500) and (A9) a Remote Interface

Assembly (1061198). The (A1) UHF Exciter Tray (1142445),

takes the Digital IF Input that is upconverted to the On Channel RF by mixing it with a L.O. signal generated by the Channel Oscillator Assembly. The RF Output of the UHF Exciter at J15 connects to (A3) a Splitter which splits the RF two ways with the RF Output #1 connected to the input of the (A5) Variable Gain/Phase Tray (1245-1200) and the RF Output #2 connected to the input of the (A4) Variable Gain/Phase Tray (1245-1200). The output of the (A4) Variable Gain/Phase Tray connects to (A2) the Side A Amplifier Assembly (1278-1300). The output of the (A5) Variable Gain/Phase Tray connects to (A3) the Side B Amplifier Assembly (1278-1300).

4.1.1 Control and Status

The Control and Status of the Transmitter are provided by the Meter indications on the Metering Panel and the Variable Gain Phase Trays. There are also Control, Status and LED Indications located on the front panel of the UHF Exciter Tray. The switches and LED indicators, which are mounted so that the switches and LEDs are operated or viewed from the front Panel of the UHF Exciter, are part of the Transmitter Control Board (1245-

1101). On the UHF Exciter Tray, switch

(S1) is an Operate/Standby Switch that provides the Operate Commands (Enables), when in Operate, to each of

the Amplifier Arrays. The Enable is needed to turn on the Switching Power Supplies located in each of the UHF Amplifier Trays. When the UHF Exciter is in Operate, the Green LED (DS2) is On and when in Standby the Amber LED (DS1) is On. NOTE: If the Transmitter does not switch to Operate, when S1 is switched to Operate, check that a Dummy Jumper Plug is connected to Jack J7, with a Jumper between Pins 1 & 2, located on (A9) the Remote Interface Assembly in the Single UHF Exciter Assembly. The Jumper provides the Interlock to the UHF Exciter needed for the operation of the Transmitter. If the Interlock is present, the Green LED (DS5), located on the Transmitter Control Board, should be lit.

Operation of the Transmitter is controlled by the front panel switches located on the UHF Exciter Tray. During Normal operation of the Transmitter, Switch S2 should be in the Auto position. The front panel of the UHF Exciter also has LEDs that indicate a Input Fault (Loss), Red LED (DS9) and a VSWR Cutback, Amber LED (DS7).

4.1.2 Digital Input and Remote Connections

The Digital Input to the Transmitter, connects to the (A9) Remote Interface Panel located on the rear of the Single UHF Exciter Assembly. The Digital Input connects to Jack J2 that is cabled to J2 on the DM8-R Modulator.

Remote Monitoring and Operation of the Transmitter is provided through the Jacks (J8, J9 & J10) located on (A9) the Remote Interface Assembly mounted toward the rear of the Single UHF Exciter Assembly. Jack (J7) should have a dummy plug connected to it,

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