UBS Axcera 840A Users Manual
10-kW UHF Transmitter with Chapter 2, System Description
Feedforward Driver
Chapter 2
System Description
The 840A (1064941) is a complete 10kW UHF internally diplexed television
transmit ter that operates at a nominal
visual output power of 10,000 watts peak
sync visual and an average aural output
power of 1000 watts with a 10 dB
aural/vis ual ratio.
2.1 System Overview
The 840A is made up of three cabinet
assemblies: the (A1) dual 250-watt
driver/amplifier assembly (1064946);
Table 2-1. Driver/Amplifier Assembly Assemblies and Trays
DESIGNA TIO N NUMBE R TRAY/ASS EMB LY NAME DRAWING NUMB E R
A2 AC distribution assembly 1265-1600
A4 UHF exciter tray 1063301
A9 3-wa tt am p lifi er tra y 10682 03
A6 and A7 250-watt amplifier trays
A14 Bandpass filter assembly --
(A2) the 10-kW ampl ifier assembly
(1299-1100); and (A3) the high-voltage
power suppl y assembly, 208/240 VAC
(1068022).
2.1.1 (A1) Dual 250-Watt
Exciter/ Amplifier Asse m bly
(1064946; Appendix A)
The dual 250-watt d river/amplifier
assembly is made up of the assemblies
and trays shown in Table 2-1.
10440 27, low -b a nd ;
1044028, mid-band;
10440 29, h igh-b a nd
The exciter/amplifier assembly
(1064946) is connected to the baseband
video and aural inputs. The assembly
also provides connections for the remote
monit oring and operation of the
exciter/amplifier assembly. The UHF
exciter tray (1063301) takes the
baseband aural and video inputs and
produces the visual and aural RF signals
on the channel frequencies. The
combined visual and aural RF output (+7
dBm) of the exciter feeds the 3-watt
amplifier tray (1068203). The 3-watt
amplifier tray contains an automatic gain
control circuit and two 3-watt amplifier
boards. The tray generates the output
level needed to drive the 250-watt
amplifier trays (1044027, low-band;
1044028, mid-band; and 1044029, highband).
The output from the 3-watt tray is fed to
the (A10) RF hyb rid spli tte r SMA
connection J1. The RF hybrid splitter
output f eeds the RF signal to one of the
250-watt amplifiers directly and, through
(A5) the line stretcher, to the other 250wa tt amplifier. The line stretcher gives
the operator the ability to control the
phase of the output signal that is fed to
one of the 250-watt trays. Each of the
250-watt amplifier trays contains an
amplifier enclosure and feedforward
circuits to achieve an output of 250-watts
peak visual power and 25 watts of aural
power.
In the 250-watt amplifier tray, a forward
power samp le from the UHF coupler is
connected to the dual peak detector
board; this board provides a peakdetected fo rward sample to the amplifier
control board for metering purposes.
Before exiting the 250-watt amplifier
tray, the RF is fed through a circulator for
the protection of the tray from high
VSWR conditions. The reject port of the
circulator is cabled to the reject
840A, Rev. 0 2-1
10-kW UHF Transmitter with Chapter 2, System Description
Feedforward Driver
load/coupler board; this board supplies
the reflected sample to the dual peak
detector board, single supply. This signal
is then sent to the amplifier control board
for metering purposes. The output of the
250-watt visual amplifier trays is
combined in a UHF tee combiner, and fed
through (A14) a bandpass filter and
(A11) a directional coupler, before being
connected with1/2" heliax to the RF input
jack (A2-A1-J1) of the tube cavity
assembly in the 10-kW am plifier
assembly cabinet. The combined output
of the 250-watt visual amplifier trays
(350 watts) is t he level needed to drive
the 10-kW amp lifi er to 10,0 00 watts
peak sync visual output.
The ma in AC input to t he
exciter/amplifier assembly is (A2) the AC
distribution panel assembly (1265-1600).
The AC distribution panel assembly
contains a terminal block (TB1) that
connects to the main AC input (208/240
VAC). The terminal block has four metaloxide varistors (MOVs) connected across
the i nput lines for surge and transient
protection. The AC distribution panel
contains CB1, the 40-amp main AC
circuit breaker that distributes the AC
through the circuit breakers CB2 to C B7
to the exciter and amplifier trays.
2.1.2 (A2) 10-kW Diacrode Amplifier
(1299-1100; Appendix A)
The (A11) metering control panel (1293-
1308) on the amplifier assembly provides
the operator with front panel metering
for all voltage (M1 using S1) and current
(M2 using S3) readings that apply to the
tube. The metering control panel also
provides the aural, visual, and reflected
output power readings for the transmitt er
using meter M3 with switch S4. The front
panel assembly contains the switches
that control the Operate/Standby (S5)
and Automatic/Manual (S6) operation of
the 10-kW amp lifie r. When sw itch ed to
Operate, the panel supplies the driv er
enable (Operate command) to the
exciter/amplifier assembly. The
Automatic/Manual switch selects either
the automatic operation of the
transmitter, which uses the video input
to control the on/off state of the
transmitter, or the Normal front panel
control, manual operation, of the
transmitter. The metering control panel
also provides front panel c ontrol, through
switch S8, of the Visual Output Power
level. High-Volta ge Enable/Disable switch
S7 controls the high-voltage power
supply from the front panel of the 10-kW
diacrode amplifier. Normal/Exciter Test
switch S10, when in the Exciter Test
position, gives the o perator the ability to
operate the exciter/am plifier assembly
without operating the 10-kW amplifier.
Note: The exciter/amplifier assembly
output must be terminated into a
dummy load prior to using this
function
The metering control panel also has LEDs
on the f ront panel for a visual indication
of the operating status of the
transmitter: Operate/Standby,
Auto/Manual, High Voltage
Enable/Disable, Driver Mode
Norma l/Test, 3-Fau lt wit h Fault Rese t
Switch (S9), Fault Status Overtemp, and
VSWR Cutback. The front panel has
command status LEDs that indicate,
when they are lit, tha t the comm and has
been given. I n addition, the front panel
has Operate status LEDs that indicate,
when they are lit, tha t the comm and has
been carried out.
The metering control panel of the (A10)
remote control and cabinet interface
assembly provides intercabinet control
and mo nitoring for the exciter and highvoltage cabinets. The remote control and
cabinet interface assembly also provides
remote access to the transmitter for
monit oring and control purposes.
The (A6) screen power supply assembly,
60 Hz (1293-1321), in the rear
compartment of the amplifier cabinet,
produces the 500 VDC at 60 mA for the
tube. The (A5) control and bias power
supply assembly (1181-1402) contains
.
840A, Rev. 0 2-2
10-kW UHF Transmitter with Chapter 2, System Description
Feedforward Driver
two separate power supplies: the control
power supply and the bias power supply.
The control power supply produces the
±12 VDC to the metering circui ts (peak
detectors) in the 10-kW amplifier as well
as the fault sensing boards, differential
buffer boards, and control logic boards in
the metering control panel. The bias
power supply produces the -80 VDC bias
voltage to the tube. R1, the bias voltage
adjustment, is located behind the
metering control panel. It sets up the
idling current (1.5 amps), no RF drive, by
adjusting the bias voltag e. The (A3)
filament power supply assembly (1299-
1107) produces the 5.2 VDC to the
filament of the tube. The 10-kW
assembly also has (A16) a blower
assembly (1293-1325) that provides the
coolant air flow to the tube mounted in
the cavity assembly.
The RF output of the 10-kW amplifier at
(A2- A1-J2) is fed th rough a 3-1/ 8"
hardline to (A2) an output coupler (1020-
1043) that provides a reflected power
sample for fault and VSWR cutback
protection. The output at (A2-A2-J2)
connects to two UHF trap filters. The trap
filters screen out the -3.58-MHz, -4.5MHz, +8.08-MHz, and +9.00-MHz
intermodulation products as well as the
second visual harmonic frequency. The
output of the trap filter is fed through
(A1 8 ) the output coupler (1020-1002)
that provides a reflected and forward
power sample to (A19) the visual/aural
mete ring assembly (1162-1402) for
metering purposes. The output of the
couple r is then fed to the ante nna.
2.1.3 (A3) High-Voltage Power
Supply Assembly, 208/240 VAC
(1068022; Appendix A)
The (A3) high-voltage power supply
assembly, 208/240 VAC (1068022),
provides the 10-kW amplifier, through
TB4, with the AC voltage that the
assembly needs to operate. It also
supplies the AC needed to operate the
blower assembly, through TB6, and the
hig h-voltage, usi ng 18 AW G 29- k V
rubb er insu la te d wi res , need e d to
operate the tube in the 10-kW amplifier.
The high-voltage power supply produces
the 50 00 VDC a t 4.00 a mp s , ma ximum
current (black picture), or 1.5 amps
idling current (no RF drive applied) for
the plate (anode) of the tube. The
assembly contains (A1) the high-voltage
transformer (1293-6103), (A5, A6, and
A7) the thre e high -voltage rectifier
boards (1293-1101), (A8, A19, A22, and
A23) filter capacitors, and (A16) the
choke tha t genera te the high vol tag e.
The high-voltage power supply assembly
also contains the power supply metering
boards, the isolation relay boards, the
circuit breakers needed to supply highvoltage metering, high voltage-on sense,
the power-on sequence, the switching on
and off, and the protection of the high
voltage. The high-voltage power supply,
at TB2, is connected to the 10-kW
assembly that provides the +12 VDC for
metering, switching, and the Enable to
the high-voltage power supply.
2.1.4 (A19) Visual/Aural Metering
Assembly (1162-1402; Appendix A)
The visual/aural metering assembly
consists of (A1) a single peak detector
board (1162-1403) for the reflected
output metering. It also contains (A2) a
visual/ aural metering board (1161-1103
or 1161-1115) for aural output and visual
output power levels and reflected power
level for VSWR protection.
840A, Rev. 0 2-3
The visual/aural metering assembly takes
the forward and reflected power samples
from the (A2-A2) and the (A18) output
couplers. The assembly provides the
metering control panel on the front panel
meters with visual, aural, and refle cted
levels for remote monitoring and VSWR
protection.
The visual/aural metering assembly
consists of (A1) a single peak detector
board (1162-1403) for the reflected
10-kW UHF Transmitter with Chapter 2, System Description
Feedforward Driver
output metering. It also contains (A2) a
visual/ aural metering board (1161-1103
or 1161-1115) for aural output and visual
output power levels and reflected power
levels for VSWR protection.
2.2.1 Exciter/Driver Cabi net
2.2.1.1 UHF Exciter Tray
Table 2-2. 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 or frequency
level is read on one of the two bottom scales. A full-scale
reading on the top scale is 120%; 100% is equivalent to the
full-rated 350 watts peak of sync visual. This meter also reads
% Aural Power, % Exciter Power, audio levels, video levels, and
ALC le v e ls .
With Sw itch S3 in
Position
Switch (S3), Meter
Meter (A4-A18)
Audio
ALC
(0 to 10 V)
% Exciter
(0 to 120)
% Aural Power
(0 to 120)
% Visual Power
(0-120)
Video
(0-1V)
2.2 Control and Status
Information on the control and status of
this system is provided by control,
status, and LED indicators and meters on
the front panel of the trays. The functions
of these control and status indicators are
de sc rib e d in the fo llo wing ta b l es .
Display
Selects the desired ALC voltage
reading, % Excit er Pow er, % Visual
Power, % Aural Power, video levels, or
aud io leve ls.
Reads the audio level, ±25 kHz
balanced or ±75 kHz composite, on
the 0 to10 (0 t o1 00 kHz ) scal e.
Indicates baseband audio if it is
connected to the transmitter and even
with the video + 4.5 MHz SCA input
selected.
Reads th e ALC voltage l evel, .85
VDC, on the 0 to10 scale
Reads the % Exciter Output Power
level needed to attain 100% output of
the transmitter on the top scale
Reads the % Aural Output Power of
the excite r/dr iver as sem bly
(100%=45 watts at 10 dB A/V ratio)
on the top scale
Reads the % Output Power of the
exciter/driver assembly (100%=450
watts peak sync) on the top scale
Reads the video level, 1V at white, on
the 0-10 scale
840A, Rev. 0 2-4
10-kW UHF Transmitter with Chapter 2, System Description
Feedforward Driver
Table 2-3. UHF Exciter Tray Control Switches
SWITCH FUNCTION
The momentary switch (S1) applies a
ground to K1, a latching relay on the
transmitter control board. K1 will switch
Transmitter (S1)
Operate/Standby
Mode Select (S2)
Auto/Manual
Power Adjust (R1)
either to Operate or to Standby, depending
on which direction S1 is pushed. When
switched to Operate, the low Enable
commands are applied to the four UHF
amplifier trays. The opposite occurs when
S1 is switched to Standby.
The momentary 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
from the ALC board will control the
operation of the transmi tter. The
transmitter will switch to Standby, a fter a
slig h t de lay , if the vide o input is los t and
will switch back to Operate, quickly, 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.
The 5 kΩ pot, A20, sets the ALC level on
the ALC board. This sets the output power
for the transmitter.
Table 2-4. UHF Exciter Tray Fault Indicators
FAULT INDICATOR FUNCTION
Indicates that the video input to the
Video L os s (DS9 Red )
VSWR Cutback (DS7 Amber)
transmitter has been lost. The fault is
generated on the ALC board in the UHF
exciter tray.
Indicates that the reflected power level of
the 10-kW transmitter has increased above
15%. This will automatically cut back the
output power level to 15%. T he fault is
generated on the transmitter contro l board
in the UHF exciter tray and is derived from
a peak-detected voltage in the am plifier
cabinet.
840A, Rev. 0 2-5
10-kW UHF Transmitter with Chapter 2, System Description
Feedforward Driver
Table 2-5. UHF Exciter Tray Samples
SAMPLE DESCRIPTION
A sample o f the visual IF that is taken from
f(IF)
f(IC)
f(s)
Exciter O/P
2.2.2 3-Watt Amplifier Tray
Table 2-6. 3-Wa tt Amplifier Tray Meter
the sample jack on the IF carrier ove n
oscillator board
A sample of the intercarrier signal that is
taken from the sample jack on the aural IF
synthesizer board
A sample of the channel oscillator output
that is taken from the sample jack of the
channel oscillator assembly
An output power sample of the exciter that
is taken from the UHF upconverter board
METER
Power Meter, Switch
(S1)
Tab l e 2-7. 3-Wa t t Amp l i fi er Tray Fault Indi c ato rs
FAULT INDICATOR FUNCTION
Overtemp (DS1)
AGC Override (DS2)
FUNCTION
Selects whether the % Reflected Power, % Input Power, %
Forward Power, power supply voltage, or AGC voltage is to be
viewed on the meter
With Switch S1 in position Display
Reads the % Reflected O utput
% Refl (Reflected)
% Input
% Forw a rd Pow e r
P.S. Vo lt age
AGC Voltage
Indicates that the temperature of the
heatsink, where the Q1 and Q2 currentpass transistors for the +24 VDC power
supply are mounted, is above 175° F as
sensed by the thermal switch (S2) mounted
to the heatsink. When this fault occurs, the
Enable to t he is o l at io n relay is re m ov e d
immediately.
Indicates tha t the leve l out of the 3-watt
amplifier board has requested the AGC
circuit to exceed the A GC limits. The fault is
generated on the AGC board in the 3-watt
amplifier tray.
Power (<10%)
Reads the % Input Power to
the tray (10%)
Reads the % Forward Power
(100%=3 watts CW)
Reads the power supply
voltage (+24 VDC)
Reads the AGC voltage
(2 VDC)
840A, Rev. 0 2-6
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