UBS Axcera DT830A Users Manual
INSTRUCTION MANUAL
DT830A
300-WATT 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
300-Watt Digital UHF Transmitter Table of Contents
TABLE OF CONTENTS
CHAPTER 1 INTRODUCTION
1.1 Manual Overview...................................................................................1-1
1.2 Assembly Designation Numbers ..............................................................1-1
1.3 Safety ..................................................................................................1-1
1.4 Maintenance .........................................................................................1-2
1.5 Material Return Procedure......................................................................1-2
1.6 Warranty for Axcera Products – Limited One-Year Warranty ......................1-3
CHAPTER 2 SYSTEM DESCRIPTION
2.1 System Overview .................................................................................2-1
2.1.1 8-VSB Modulator Tray...................................................................2-1
2.1.2 UHF Digital Exciter Tray ................................................................2-1
2.1.3 UHF Digital RF Output Components................................................2-2
2.1.4 Transmitter Power Requirements ...................................................2-2
2.2 Control and Status ................................................................................2-3
2.2.1 8-VSB Digital Modulator................................................................2-3
2.2.2 UHF Digital Exciter Tray ................................................................2-4
2.2.3 UHF Amplifier Trays......................................................................2-6
2.3 Remote Connections..............................................................................2-7
CHAPTER 3 INSTALLATION AND SETUP PROCEDURES
3.1 Site Considerations................................................................................3-1
3.2 Unpacking the Cabinets .........................................................................3-4
3.3 Installation of the Cabinets and Trays......................................................3-5
3.4 Setup and Operation Procedures.............................................................3-5
CHAPTER 4 CIRCUIT DESCRIPTIONS
4.1 UHF Exciter Tray ...................................................................................4-1
4.1.1 UHF Filter....................................................................................4-1
4.1.2 UHF Generator Board ...................................................................4-1
4.1.3 10-MHz Reference Generator Board ...............................................4-1
4.1.4 PLL Board....................................................................................4-2
4.1.5 Power Entry Module Assembly .......................................................4-4
4.1.6 IF Phase Corrector Board ..............................................................4-4
4.1.7 ALC Board ...................................................................................4-6
4.1.8 Visual/Aural Metering Board ........................................................4-12
4.1.9 UHF Upconverter Board .............................................................. 4-13
4.1.10 Transmitter Control Board ......................................................... 4-15
4.1.11 +12V(4A)/-12V(1A) Power Supply Board .................................... 4-19
4.1.12 5-Section Delay Equalizer Board, 44 MHz....................................4-20
DT830A, Rev. 1 i
300-Watt Digital UHF Transmitter Table of Contents
TABLE OF CONTENTS (continued)
4.2 8-VSB Digital Modulator.......................................................................4-20
4.2.1 Vector Modulator Board .............................................................. 4-20
4.2.2 Switch Board ............................................................................. 4-21
4.2.3 Local Oscillator Board .................................................................4-21
4.2.4 LED Board.................................................................................4-22
4.2.5 VSB Modulator Interface Board.................................................... 4-22
4.2.6 VSB Filter Board......................................................................... 4-22
4.2.7 DC Power Supply Board .............................................................. 4-23
4.2.8 VSB IF Filter Board..................................................................... 4-23
4.2.9 VSB Symbol Generator Board...................................................... 4-23
4.3 UHF Amplifier Trays............................................................................. 4-23
4.3.1 1-Watt Amplifier Board Assembly................................................. 4-23
4.3.2 1-Watt Amplifier Board ............................................................... 4-24
4.3.3 4-Way Splitter Assembly............................................................. 4-24
4.3.4 4-Way Splitter Board..................................................................4-24
4.3.5 Coupler Board Assembly ............................................................. 4-25
4.3.6 Dual Peak Detector Enclosure......................................................4-25
4.3.7 Dual Peak Detector Board, Single Supply...................................... 4-25
4.3.8 Dual Stage Amplifier Assembly, Mid Band, Class AB.......................4-26
4.3.9 Generic Dual Stage Amplifier Board, Class AB ............................... 4-27
4.3.10 Amplifier Protection Board......................................................... 4-27
4.3.11 Amplifier Control Board.............................................................4-28
4.3.12 Single Stage Amplifier Assembly, Mid Band, Class A..................... 4-30
4.3.13 Generic Single Stage Amplifier Board, Class A .............................4-31
4.3.14 Variable Gain/Phase Board Enclosure.......................................... 4-31
4.3.15 Variable Gain/Phase Board ........................................................ 4-32
4.3.16 4-Way Combiner Assembly........................................................4-33
CHAPTER 5 DETAILED ALIGNMENT PROCEDURES
5.1 UHF Exciter Tray ...................................................................................5-1
5.1.1 Delay Equalization Adjustment ......................................................5-2
5.1.2 IF Phase Corrector Adjustment ......................................................5-3
5.1.3 UHF Generator Board ...................................................................5-4
5.1.4 10-MHz Reference Generator Board ...............................................5-4
5.1.5 PLL Board....................................................................................5-4
5.2 UHF Amplifier Trays ..............................................................................5-6
5.2.1 Phase and Gain Adjustment of the UHF Amplifier Trays ....................5-7
DT830A, Rev. 1 ii
300-Watt Digital UHF Transmitter Table of Contents
TABLE OF CONTENTS (continued)
5.3 8-VSB Modulator....................................................................................5-8
5.3.1 VSB Modulator Interface Board......................................................5-9
5.3.2 VSB Symbol Generator Board........................................................5-9
5.3.3 VSB Filter Board......................................................................... 5-11
5.3.4 Switch Board ............................................................................. 5-13
5.3.5 Local Oscillator Board .................................................................5-13
5.3.6 VSB Vector Modulator Board ....................................................... 5-14
5.3.7 DC Power Supply Board .............................................................. 5-14
5.3.8 VSB IF Filter Board..................................................................... 5-15
5.3.9 LED Board.................................................................................5-15
5.3.10 Offset Adjust............................................................................ 5-15
5.3.11 Local Oscillator Leak-Through Adjustment................................... 5-15
5.3.12 I and Q Baseband Frequency Response Adjustments....................5-16
5.3.13 Gain and Quadrature Adjustments ............................................. 5-16
5.3.14 Output Level Adjust.................................................................. 5-16
5.4 Output Power Level ............................................................................. 5-17
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 DT830A SYSTEM SPECIFICATIONS
DT830A, Rev. 1 iii November 1, 2002
300-Watt Digital UHF Transmitter Table of Contents
LIST OF FIGURES
2-1 Remote Interface Panel...................................................................2-8
3-1 1 kW Minimum Ventilation Configuration ..........................................3-4
5-1 Typical Digital Spectrum .................................................................5-3
DT830A, Rev. 1 iv
300-Watt Digital UHF Transmitter Table of Contents
LIST OF TABLES
2-1 DT830A Major Assemblies and Trays ................................................2-1
2-2 Digital Modulator Display ................................................................2-3
2-3 Digital Modulator Control Pushbuttons..............................................2-4
2-4 Digital Modulator Status Indicators...................................................2-4
2-5 Digital Modulator Sample ................................................................2-4
2-6 UHF Exciter Tray Meters..................................................................2-4
2-7 UHF Exciter Tray Controls ...............................................................2-5
2-8 UHF Exciter Tray Fault Indicators .....................................................2-5
2-9 UHF Exciter Tray Samples ...............................................................2-6
2-10 UHF Amplifier Tray Meters...............................................................2-6
2-11 UHF Amplifier Tray Status Indicators................................................2-7
2-12 UHF Amplifier Tray Controls ............................................................2-7
2-13 UHF Amplifier Tray Sample..............................................................2-7
2-14 UHF Exciter Remote Connections .....................................................2-9
2-15 UHF Amplifier Tray Remote Connections ......................................... 2-10
4-1 Fuses, Idling Currents, and Voltage Settings for the
Class AB Amplifier Devices ............................................................4-28
5-1 Jumper Positions on the 6-dB Pad ....................................................5-1
5-2 Center Frequencies for the Delay Equalizer Sections ..........................5-3
5-3 PLL Board Switch Positions..............................................................5-5
5-4 PLL Board Switch Positions for Channel Frequencies...........................5-5
5-5 8-VSB Modulator Connections..........................................................5-8
5-6 Jumper Configurations for the Symbol Generator Board ................... 5-10
5-7 Jumper Configurations for the VSB Filter Board ............................... 5-12
5-8 DIP Switch Settings...................................................................... 5-13
DT830A, Rev. 1 v
300-Watt UHF Digital Transmitter Chapter 1, Introduction
Chapter 1
Introduction
This manual explains the installation,
setup, alignment, and maintenance
procedures for the DT830A 300-watt
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
five chapters and supporting appendices.
Chapter 1, Introduction, contains
information on safety, the Axcera method
of assigning assembly designation
numbers, maintenance, return
procedures, and warranties. The second
chapter describes the transmitter and its
system control and status indicators and
remote control connections. Chapter 3
explains how to unpack, install, set up,
and operate the transmitter. Chapter 4,
Circuit Descriptions, describes the circuits
that make up the trays and assemblies in
the transmitter. 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 product information for vendorsupplied products used in the
transmitter.
1.2 Assembly Designation Numbers
Axcera has assigned assembly numbers,
such as Ax (x=1,2,3…), to all assemblies,
trays, and boards that are referenced in
the text of this manual and shown on the
block diagrams and interconnect
drawings provided in the appendices.
These supporting documents are
arranged in increasing numerical order in
the appendices. Section titles in the text
for assembly or tray descriptions or
alignment procedures also indicate the
associated part number(s) and the
relevant appendices. Sections describing
vendor-supplied items, such as meters
and power supplies, do not contain this
information.
1.3 Safety
The 300-watt UHF transmitters
manufactured by Axcera are designed to
be easy to 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.
DT830A, Rev. 1 1-1
300-Watt UHF Digital Transmitter Chapter 1, Introduction
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 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
hazards. Please contact the Axcera
Technical Service Department if you have
any questions regarding service or
replacement parts.
Caution: Because the capacitors
used in the high-voltage circuits
have the potential of recharging
themselves, care must be taken
when handling them. The capacitors
should first be shorted with a
grounding stick and then a piece of
wire should be connected across the
terminals until they can be put into
service. Remember to remove the
shorting wire before energizing the
high-voltage supply.
1.4 Maintenance
The DT830A 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 and time interval 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
hinder the effectiveness of the cooling of
the components. This could lead to a
thermal shutdown or the 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 should be removed. A
vacuum cleaner, utilizing a small, wandtype 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 for the life of the equipment.
A sample format for a log sheet is
provided in Appendix A. Photocopies of
the log sheet should be made for future
data entries.
1.5 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.
DT830A, Rev. 1 1-2
300-Watt UHF Digital Transmitter Chapter 1, Introduction
Note: To prevent damage to the
product during shipping, Axcera will
supply a shipping container to the
customer at no cost.
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 the customer being
invoiced 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 Axcera-provided 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 Axcera Field Service at
(724) 873-8100 or by fax at (724)
873-8105.
Axcera can also be contacted through email at info@axcera.com and on the Web
at www.axcera.com.
1.6 Warranty for Broadcast Products
– Limited One-Year Warranty
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.
DT830A, Rev. 1 1-3
300-Watt Digital UHF Transmitter Chapter 2, System Description
Chapter 2
System Description
The DT830A is a complete 300-watt
(average) UHF solid-state digital
television transmitter that operates at a
nominal average output power of 300
watts.
Table 2-1. DT830A Major Assemblies and Trays
MAJOR ASSEMBLY NUMBER TRAY/ASSEMBLY NAME
A4 UHF digital exciter tray
A6 and A7 UHF amplifier trays
A11 Coupler assembly
A2 AC distribution assembly
A19 8-VSB modulator tray
A12 Input and remote interface assembly
A8 UHF “tee”
2.1.1 (A19) 8-VSB Modulator Tray
(1075164; Appendix C)
The 8-VSB modulator accepts an MPEG2 transport stream input and outputs an
8 VSB IF signal centered at 44 MHz. To
operate the modulator, the MPEG is
connected to one of the three
connectors on the rear panel, depending
on the format of the MPEG data stream.
The formats presently available are
SMPTE 310M, Differential Serial TTL, and
ECL. In addition, the modulator has an
internal test source that can generate an
MPEG data stream for test purposes.
This signal is then modulated to a 44
MHz IF and fed to the output at J1.
2.1.2 (A4) UHF Digital Exciter Tray
(1294-1111; Appendix C)
The output from the modulator connects
to J6 on the rear of the UHF exciter tray,
which is wired to J18 on the IF delay
equalizer board, 44 MHz (1072090) and
exits the board at J10. The processed
digital IF signal is then wired to the ALC
board (1265-1305) at J32. With digital IF
input selected, the jumper W11 on J29 is
connected 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
2.1 System Overview
The DT830A consists of the assemblies
and trays listed in Table 2-1.
ALC board. The LED DS5, digital IF
modulator enable, should be lit. The ALC
board has the capability to switch
between two different IF inputs; in this
case, only the digital IF input is used.
The output of the ALC board (0 dBm
peak) 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.
DT830A, Rev. 1 2-1
300-Watt Digital UHF Transmitter Chapter 2, System Description
The (A14-A1) 10-MHz reference
generator board (1519-1126) is located
in (A10) the 10-MHz reference kit (1286-
1108). The board contains a highstability 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, 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.
2.1.3 UHF Digital RF Output
Components
The RF output of the UHF exciter is fed to
an (A5) splitter and then to two UHF
amplifier trays that amplify the RF signal
to approximately 300 watts. A forward
power sample from the 4-way combiner
board inside each tray is connected to
the dual peak detector board that
provides a peak-detected forward sample
to the amplifier control board. This board
supplies the sample to the front panel
meter of the UHF amplifier tray.
Before exiting the UHF amplifier tray, the
RF is fed through a circulator to protect
the tray from high VSWR conditions. The
reject port of the circulator provides a
reject sample to the 4-way combiner
board that supplies the reflected sample
to the dual peak detector board. The
reflected sample connects to the
amplifier control board that provides the
sample to the front panel meter of the
tray. The output of (A6 and A7) the UHF
amplifier trays are combined in a tee and
then provide approximately 550 watts
average power. The output is connected
to a bandpass filter and then to the
output coupler assembly. There is a
coupler on the output of the bandpass
filter that provides –40 dB forward and
reflected samples to the system control
panel. The bandpass filter is tuned to
provide high out-of-band rejection of
unwanted products. The 7/8" coupler
assembly provides two forward power
samples and one reflected power sample.
The forward and reflected samples are
cabled to the visual/aural metering
boards in the UHF exciter. The forward
and reflected samples are processed to
provide detected power output samples
to the transmitter control board. The
transmitter control board connects the
forward and reflected power output
samples to the front panel meter for
monitoring.
2.1.5 Transmitter Power
Requirements
The transmitter needs an AC input of 220
VAC at 40 amps, or 80 amps for the
upgradeable version, connected to it in
order to operate. The 220 VAC input
connects to terminal block (TB1) in the
upper right rear of the cabinet and is part
DT830A, Rev. 1 2-2
300-Watt Digital UHF Transmitter Chapter 2, System Description
of the (A2) AC distribution panel. The AC
distribution panel contains four circuit
breakers, six in the upgradeable version,
which supply the AC to the rest of the
transmitter.
The input AC from TB1 is connected to
(CB1) the main AC circuit breaker (40
amps for DT830A and 80 amps for the
upgradeable version) which distributes
the 220 VAC to the terminal block (TB2).
TB2 has three MOVs mounted to the
terminal block: one is connected from
each leg of the input AC to ground and
the other one is connected across the
two legs.
The input AC is wired from TB2 through
three circuit breakers, CB2, CB3 and
CB4, CB5 and CB6 are used in the
upgradeable version, to the rest of the
transmitter. CB2 (10 amps) supplies the
AC voltage to the IEC outlet strip (A1)
into which the UHF exciter and any other
optional accessories are connected. CB3
(20 amps) supplies AC through J5 to (A6)
the UHF amplifier tray. CB4 (20 amps)
supplies AC through J6 to (A7) the UHF
amplifier tray. In the upgradeable
version, CB5 (20 amps) supplies AC
through J6 to (A8) the UHF amplifier tray
and CB6 (20 amps) supplies AC through
J6 to (A9) UHF amplifier tray. .When the
UHF exciter circuit breaker is switched
on, +12 VDC is supplied to the UHF
amplifier tray for the operation of the
LED status indicators in the tray.
2.2.1 (A19) 8-VSB Digital Modulator (1075164; Appendix C)
Table 2-2. Digital Modulator Display
DISPLAY FUNCTION
LCD
The front panel has three pushbuttons for the control of the external and internal
functions.
2.2 Control and Status
Control and status indications of the
transmitter are provided by the meters
and LED indicators on the front panel of
the UHF exciter. The switches and LED
indicators are part of the transmitter
control board (1265-1311) which is
mounted so that the switches and the
LEDs can be operated or viewed from the
front panel of the UHF exciter. Switch S1
is an Operate/Standby switch that
controls the output of the transmitter by
providing the Enables, when in Operate,
needed to turn on the switching power
supplies in the two or four UHF amplifier
trays. In Operate, the green LED DS2 is
on and in Standby the amber LED DS1 is
on.
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 23 and 24, is
connected to jack J11 on the rear of the
UHF exciter tray or with a jumper
between pins 21 and 22 on jack J9 on
(A17) the (optional) input and remote
interface panel. This jumper provides the
interlock needed for the transmitter to
operate. If the interlock is present, the
green LED DS5 on the transmitter control
board should be lit. The front panel of the
UHF exciter also has an LED for VSWR
cutback (amber LED DS7).
Provides a three-line readout of the internal
functions, external inputs, and status. See
Chapter 4, Detailed Alignment Procedures,
for a listing of display parameters.
DT830A, Rev. 1 2-3
300-Watt Digital UHF Transmitter Chapter 2, System Description
Table 2-3. Digital Modulator Control Pushbuttons
PUSHBUTTON FUNCTION
Menu
Up Arrow (↑)
Down Arrow (↓)
Controls which menu is displayed on the
LCD readout
Moves the active line up one position on the
LCD display
Moves the active line down one position on
the LCD display
There are four front panel status indicator LEDs.
Table 2-4. Digital Modulator Status Indicators
LED FUNCTION
Indicates the presence of an MPEG-2 signal;
MPEG (Green)
can be internal or external depending on
menu selection
REF (Green)
PLL Locked (Green)
Power (Green)
Indicates the presence of an external 10
MHz reference source
Indicates that the phase-locked loop circuit
is functioning and locked
Indicates that the DC power supply is
functioning
Table 2-5. Digital Modulator Sample
SAMPLE DESCRIPTION
Front panel sample Sample of the 44 MHz IF output
2.2.2 (A4) UHF Digital Exciter Tray (1294-1111; Appendix C)
Table 2-6. UHF Exciter Tray Meters
METER FUNCTION
Reads power in terms of a percentage of
the calibrated output power level on the
upper scale. The voltage level is read on
one of the bottom two scales. A full scale
Meter (A4-A18)
reading on the top scale is 0-120%, which
is equivalent to the full-rated 300 watts or
1000 watts in the upgradeable version,
average power. Also reads % Exciter
Power, % Reflected Power, and ALC
reading.
Selects the desired ALC voltage reading, %
Switch (S3), meter
Exciter Power, % Output Power, and %
Reflected Power
ALC
(0-1 V)
Reads the ALC voltage level, .8 VDC, on
the 0-10 scale
DT830A, Rev. 1 2-4
300-Watt Digital UHF Transmitter Chapter 2, System Description
METER FUNCTION
% Exciter
(0-120)
% Output power
(0-120)
% Reflected
(0-120)
Reads the % Exciter Output Power level
needed to attain 100% output of the
transmitter on the top scale
Reads the % Output Power of the
transmitter on the top scale
Reads the % Reflected Output Power, <5%,
on the top scale
Table 2-7. UHF Exciter Tray Controls
SWITCH FUNCTION
The momentary switch (S1) applies a
ground to K1, a latching relay on
the transmitter control board. K1 will switch
either to Operate or to Standby
Transmitter (S1)
Operate/Standby
depending on which direction S1 is pushed.
When switched to Operate, the low Enable
commands are applied to the two or four
600-watt amplifier trays. These Enables will
turn on the 600-watt 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 Video Fault command
Mode Select (S2)
Auto/Manual
from the ALC board will control the
operation of the transmitter. The
transmitter will switch to Standby, after a
slight delay, if the input video is lost. It will
quickly switch back to Operate when the
video is restored. In Manual, the transmitter
is controlled by the operator using the front
panel Operate/Standby switch or by remote
control.
Pot A20 sets the ALC level on the ALC
Power adjust (R1)
board to set the output power of
the transmitter.
Table 2-8. UHF Exciter Tray Fault Indicators
INDICATOR FUNCTION
Indicates that the reflected power level of the
transmitter has increased above 20% which will
VSWR cutback (DS7 amber)
automatically cut back the output power level to
20%. The fault is generated on the transmitter
control board in the UHF exciter tray.
DT830A, Rev. 1 2-5
300-Watt Digital UHF Transmitter Chapter 2, System Description
Table 2-9. UHF Exciter Tray Samples
SAMPLE DESCRIPTION
A sample of the channel oscillator output,
f(s)
taken from the sample jack of the channel
oscillator assembly
Exciter O/P
An output power sample of the exciter
taken from the UHF upconverter board
A forward power sample of the transmitter
Transmitter O/P
taken from the visual/aural metering board
before the signal reaches the bandpass
filter
2.2.3 (A6 and A7) UHF Amplifier Trays (1294-1112 Low Band, 1294-1113 Mid
Band or 1294-1114 High Band ; Appendix C)
Table 2-10. UHF Amplifier Tray Meters
METER FUNCTION
Reads power in terms of a percent of the
calibrated power output value. A full-scale
Meter (A6)
reading is 100%, which is equivalent to the
full-rated 300 watts of average power. Also
reads % Reflected Power, power supply,
and AGC voltage levels.
Switch (S2), meter
Selects the desired % Power or the voltage
reading
% Output pwr Displays the % Output Power of the tray
% Refl (Reflected)
Power supply
AGC voltage
Displays the % Reflected Output Power of
the tray, <10% on the top scale
Reads the power supply voltage, +26.5
VDC, on middle scale
Reads the AGC voltage level, +1 to +2
VDC, on the bottom scale
DT830A, Rev. 1 2-6
300-Watt Digital UHF Transmitter Chapter 2, System Description
Table 2-11. UHF Amplifier Tray Status Indicators
INDICATOR FUNCTION
Indicates that an Enable, Operate,
Enable (DS4 green)
command is applied to the UHF amplifier
tray from the UHF exciter tray
Indicates that the level of the drive is too
Overdrive (DS2 red)
high. The protection circuit will limit the
drive to the set threshold. The fault is
generated on the amplifier control board.
Indicates that the reflected power level of
the tray has increased above 50%, which
VSWR cutback (DS1 red)
will automatically cut back the output power
level to 50%. The fault is generated on
the amplifier control board.
Indicates that the temperature of (A5-A6A3 and A5-A6-A4) one or both of the two
thermal switches mounted on the heatsink
Overtemp (DS3 red)
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 removed
immediately and it will shut down.
Input fault (DS5 red)
Indicates that the input RF level to the
amplifier tray dropped below 0 dBm
Table 2-12. UHF Amplifier Tray Controls
CONTROL FUNCTION
Phase (A10-R5)
Gain (A11-R6)
Adjusts the phase of the RF output with a
range of approximately 90°
Adjusts the gain of RF output when the
amplifier control board is in the AGC mode
Table 2-13. UHF Amplifier Tray Sample
SAMPLE DESCRIPTION
A sample of the combined output of the
Module O/P (0 dBm)
four dual-stage amplifier boards taken
from the dual peak detector board
2.3 Remote Connections
The IF input to the transmitter connects
to the rear of the UHF exciter or to (A12)
the input and remote interface panel
(Figure 2-1). Jacks J10 and J11 on the
rear of the UHF exciter provide
connections for the remote monitoring
and operation of the transmitter. Jack
J11 should have a dummy plug
connected to it with a jumper between
pins 23 and 24 that provides the
interlock needed to operate the
transmitter. If remote connections are
made to the transmitter, they should be
made through the plug in J10 or J11 in
the positions noted on the interconnect
drawing (1127833).
DT830A, Rev. 1 2-7
300-Watt Digital UHF Transmitter Chapter 2, System Description
Figure 2-1. Remote Interface Panel
The remote connections shown in Tables
2-14 and 2-15 are made if (A12) the
input and remote interface assembly is
present in the system. The remote
connections are made to jacks J9 and J10
on the assembly. Refer to the
interconnect drawing (1127833) for the
proper pin remote connections.
DT830A, Rev. 1 2-8
300-Watt Digital UHF Transmitter Chapter 2, System Description
Table 2-14. Remote Interface Panel Connections
FUNCTION REMOTE JACK/PIN
NUMBER
Transmitter Enable Interlock J9-21
Transmitter Enable Interlock
Rtn
Remote Control Commands
Transmitter Standby
(Disable)
Transmitter
Standby/Operate Rtn
Transmitter Operate
(Enable)
Transmitter Manual J9-15 Contact closure
Transmitter Auto/Manual
Rtn
Transmitter Auto J9-17 Contact closure
Power Level Raise (optional) J9-27 Contact closure
Pwr Level Raise/Lower Rtn
(optional)
Power Level Lower
(optional)
Remote Status Indications
Transmitter Operate
(Enable) Ind
Operate/Standby Ind.
Return
Transmitter Standby
(Disable) Ind
Transmitter Auto Indicator J9-18 50 mA max current sink
Auto/Manual Indicator
Return
Transmitter Manual
Indicator
VSWR Cutback Indicator J9-23 50 mA max current sink
VSWR Cutback Indicator
Return
J9-22
J9-9
J9-10
J9-11
J9-16
J9-28
J9-29
J9-12
J9-13
J9-14
J9-19
J9-20
J9-24
INTERFACE TYPE
J9-21 and 22 must be
jumpered for normal
operation; (1176-1038)
jumper jack is used.
Contact closure
Contact closure
Contact closure
50 mA max current sink
50 mA max current sink
50 mA max current sink
DT830A, Rev. 1 2-9
300-Watt Digital UHF Transmitter Chapter 2, System Description
FUNCTION REMOTE JACK/PIN
NUMBER
Remote Metering
Digital Output Power J9-1
Digital Output Power Rtn J9-2
Reflected Power J9-5
Reflected Power Rtn J9-6
Exciter Output Power J9-7
Exciter Output Power Rtn J9-8
Table 2-15.UHF Amplifier Tray Remote Connections
FUNCTION REMOTE JACK/PIN
NUMBER
Forward Output Power (A6)
UHF Amp
Forward Output Power (A6)
Rtn
Reflected O/P Power (A6)
UHF Amp
Reflected O/P Power (A6)
Rtn
Forward Output Power (A7)
UHF Amp
Forward Output Power (A7)
Rtn
Forward O/P Power (A8)
UHF Amp
Forward Output Power (A8)
UHF Amp Rtn
Reflected O/P Power (A8)
UHF Amp
Reflected O/P Power (A8)
Rtn
Forward O/P Power (A9)
UHF Amp
Forward Output Power (A9)
UHF Amp Rtn
Reflected O/P Power (A9)
UHF Amp
Reflected O/P Power (A9)
Rtn
J10-1
J10-2
J10-3
J10-4
J10-6
J10-7
J10-10
J10-11
J10-12
J10-13
J10-14
J10-15
J10-16
J10-17
INTERFACE TYPE
1V full scale at 1kΩ
source resistance
1V full scale at 1kΩ
source resistance
1V full scale at 1kΩ
source resistance
INTERFACE TYPE
1V full scale at 1kΩ
source resistance
1V full scale at 1kΩ
source resistance
1V full scale at 1kΩ
source resistance
1V full scale at 1kΩ
source resistance
1V full scale at 1kΩ
source resistance
1V full scale at 1kΩ
source resistance
1V full scale at 1kΩ
source resistance
DT830A, Rev. 1 2-10
300-Watt 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
DT830A 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 40 amps and
80 amps for the upgradeable version
Make sure that the proposed site for the
transmitter has the voltage requirements
that are needed.
The DT830A 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 without
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. This is rarely 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 300-watt
transmitter itself.
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.
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.
DT830A, Rev. 1 3-1
300-Watt Digital UHF Transmitter Chapter 3, Installation and Setup Procedures
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 the ingress of dirt.
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
where dirt, leaves, snow, etc., 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
DT830A, Rev. 1 3-2
300-Watt Digital UHF Transmitter Chapter 3, Installation and Setup Procedures
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 the filters,
if used, 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.
DT830A, Rev. 1 3-3
300-Watt Digital UHF Transmitter Chapter 3, Installation and Setup Procedures
Figure 3-1. 1 kW Minimum Ventilation Configuration
3.2 Unpacking the Cabinets
Note: Air conditioning and any
related heat exhaust ducts should be
in place before continuing with the
installation of the transmitter.
Thoroughly inspect the cabinet 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 is indicative of 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 cabinet with trays, UHF tee
assembly, bandpass filter, digital
modulator, (optional) trap filter,
directional coupler, and the installation
material from the crates and boxes.
Remove the straps that hold the cabinet
to the shipping skid and slide the cabinet
from the skid. Remove the plastic wrap
and foam protection from around the
cabinet. Do not remove any labeling or
tags from any cables or connectors;
these are identification markers that
make assembly of the transmitter much
easier.
Remove the four L-brackets, mounted on
the front panel rails, which held the trays
in place during shipment. 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
and digital modulator trays. Inspect the
trays for any loose hardware or
connectors, tightening where needed.
Open the rear door and inspect the
interior for packing material, carefully
removing any 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.
DT830A, Rev. 1 3-4
300-Watt Digital UHF Transmitter Chapter 3, Installation and Setup Procedures
Caution: Each UHF amplifier tray has
a hardline coaxial cable connected to
the bottom panel. The tray will not
slide out unless this cable is first
removed. To pull the tray out for test
purposes, use the extender coaxial
cable included in the installation
material kit for connections from the
tray to the output cable.
Adjustments to the position of the trays
may be necessary. To accomplish this,
loosen the cabinet slide mounting bolts
that hold the front of the slide to the
mounting frame of the cabinet and move
the tray up or down as needed to correct
for the rubbing.
The air intake to the transmitter is
intended for room air only. The cabinet
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 main AC hookup, and the
installation of the output transmission
line. The cabinet 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 cabinet.
3.3 Installation of the Cabinets and
Trays
Once the cabinet is in place and the trays
are checked for damage, the main AC
hookup is ready to be made.
Caution: Before connecting the 230
VAC, make certain that all of the
circuit breakers associated with the
transmitter are switched off.
The main AC input circuit to the
transmitter should be a 40-amp, 80-amp
for upgradeable version, 230-VAC line,
using AWG 8 wire inside of a 1-1/4"
conduit. The 230-VAC input connections
(terminals 1 and 2 [230 VAC] and
terminal 3 [chassis ground]) are made to
terminal block TB1, which is part of (A2)
the AC distribution panel near the rear
door of the transmitter. Line 2 is the
neutral for international systems using
220 VAC hot and neutral.
The RF output at J2 of (A11) the coupler
assembly, which is 7/8" rigid coax,
should connect to the transmission line
that is connected to the antenna system.
The MPEG digital source input connects
to J3, ECL, or TTL, depending on the
configuration, at the rear panel of (A19)
the modulator or J2 on (A12) the remote
interface panel. Remote functions
connect to the rear of (A4) the UHF
exciter or to (A12) the input and remote
interface panel mounted on the rear top
of the transmitter. A plug is connected to
jack J11 with pins 23 and 24 jumpered
together on the UHF exciter or to jack J9
with pins 21 and 22 jumpered together
on the (optional) remote interface panel.
These are 37-pin, “D”-connectors that
provide the interlock for the transmitter.
Jacks J10 and J11 on the UHF exciter,
and jacks J9 and J10 on the (optional)
remote interface panel, are used to
connect the remote control functions to
the transmitter.
This completes the unpacking and
installation procedures for the DT830A
Digital UHF Transmitter. Refer to the
setup and operation procedures that
follow before applying power to the
transmitter.
3.4 Setup and Operation Procedures
The transmitter should initially be turned
on with the RF output of the bandpass
filter/coupler assembly terminated into a
dummy load of at least 500 watts. If a
load is not available, check that the
output of the coupler assembly is
connected to the antenna.
Switch on the main AC, UHF exciter,
digital modulator, and the amplifier #1
and #2, amplifier #3 and #4 are used
after upgrade, circuit breakers located on
the AC distribution panel facing the rear
DT830A, Rev. 1 3-5
300-Watt Digital UHF Transmitter Chapter 3, Installation and Setup Procedures
of the cabinet and mounted behind the
rear door. On the UHF exciter tray,
switch the Operate/Standby switch to
Standby.
Move the Operate/Standby switch,
located on the UHF exciter tray, to
Operate. Observe the power supply
reading, +26.5 VDC, on the front panel
of the UHF amplifier trays.
Note: If the transmitter does not
switch to Operate when the
Operate/Standby switch is switched
to Operate, check that an external
interlock plug, with a jumper wired
from pins 23 to 24, is connected to
jack J11 on the rear of the UHF
exciter. Or, if (A17) the optional
input and remote interface assembly
is present in the system, the external
interlock plug, with a jumper wired
from pins 21 to 22, should be
connected to jack J9 on the
assembly.
Observe the front panel meter reading in
the % Output Power position on the UHF
exciter tray; after allowing several
minutes of warm-up time, it should read
100%. If necessary, readjust the
screwdriver adjust power pot on the front
panel of the UHF exciter for 100%. As
you are checking the power level, check
the meter reading in the % Reflected
Power position. If the % Reflected Power
is very high (above 10%), a problem
with the output coaxial lines is present
and needs to be checked. A center bullet
missing from the 7/8" rigid coax lines or
loose bolts on the connections can cause
this problem. Return the Operate/
Standby switch to Standby.
The gain and phase controls on the front
panel of the UHF amplifier tray were
adjusted at the factory to attain 100%
output of the transmitter and should not
need to be readjusted. Refer to the Test
Data Sheet for the transmitter to
compare the final reading from the
factory with the reading on the tray after
the setup. They should be very similar. If
a reading is off by a significant amount,
refer to the phasing and power
adjustment procedures for the UHF
amplifier tray 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 breaker. Remove the dummy load
and make all of the connections needed
to connect the transmitter to the
antenna. Switch the main AC circuit
breaker on and the Operate/Standby
switch to operate. Adjust the output
power screwdriver pot to attain 100%
output.
If the transmitter is already connected to
the antenna, check that the output is
100%. If necessary, adjust the power
screwdriver pot.
If a problem occurred during the setup
and operation procedures, refer to
Chapter 5, Detailed Alignment
Procedures, of this manual for more
information.
This completes the setup and operation
procedures for the DT830A transmitter.
The transmitter can now be operated
normally.
DT830A, Rev. 1 3-6
300-Watt Digital UHF Transmitter Chapter 4, Circuit Descriptions
Chapter 4
Circuit Descriptions
4.1 (A4) UHF Exciter Tray (12941111; Appendix C)
4.1.1 (A12 and A18) UHF Filter
(1007-1101; Appendix D)
The UHF filter is a tunable two-section
cavity filter that is typically tuned for a
bandwidth of 5 MHz and has a loss of -1
dB through the filter.
4.1.2 (A15-A1) UHF Generator
Board (1565-1109; Appendix D)
The UHF generator board 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 VCXO produces
an output of ≈ 67 MHz to 132 MHz,
depending on the desired channel
frequency. Course adjustment to the
frequency is made by C11, while fine
adjustments are accomplished by the AFC
voltage from (A11) the PLL board (1286-
1104). The VCXO frequency level is
adjusted by C6, L2, and L4. The output is
split and provides an input to the x8
multiplier circuitry as well as a sample for
the PLL board.
The x8 circuitry consists of three identical
x2 broadband frequency doublers. The
input signal at the fundamental frequency
is fed through a 6-dB pad consisting of
R21, R24, and R25 to amplifier U3. The
output of the amplifier stage is directed
through a bandpass filter consisting of L8
and C32, which is tuned to the
fundamental frequency (67 MHz to 132
MHz). The voltage measured at TP1 is
typically +.6 VDC. The first doubler stage
consists of Z1 with bandpass filter L9 and
C34 tuned to the second harmonic (134
MHz to 264 MHz). The harmonic is
amplified by U4 and again bandpass
filtered at the second harmonic by C38
and L11 (134 MHz to 264 MHz). The
voltage measured at TP2 is typically +1.2
VDC. The next doubler stage consists of
Z2 with bandpass filter C40 and L12
tuned to the fourth harmonic of the
fundamental frequency (268 MHz to 528
MHz). The fourth harmonic is then
amplified by U5 and fed through another
bandpass filter tuned to the fourth
harmonic consisting of L14 and C44 (268
MHz to 528 MHz). The voltage measured
at TP3 is typically +2.0 VDC. The final
doubler stage consists of Z3 with
bandpass filter C46 and L15 tuned to the
eighth harmonic of the fundamental
frequency (536 MHz to 1056 MHz). The
signal is amplified by U6 and U7 to a
typical value of from +2 to +4 VDC as
measured at TP4. 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 +12 VDC for the board enters
through jack J4-3 and is filtered by L22
and C54-C58 before being distributed to
the circuits on the board.
4.1.3 (A14-A1) 10-MHz Reference
Generator Board (1519-1126;
Appendix D)
The 10-MHz reference generator board is
located in (A10) the 10-MHz reference kit
(1286-1108). The board contains a highstability 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 oscillator operates at 10 MHz.
Transistor Q1 is the oscillating transistor
with the frequency of oscillation set by
the crystal Y1. L2, C2, and C3 have
second-order effects on the frequency,
with C2 and C3 used to pull the oscillator
DT830A, Rev. 1 4-1
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