UBS Axcera 420A Low Power Television User Manual Chapter 2

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Document Description	Chapter 2
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Date Submitted	2000-01-10 00:00:00
Date Available	2000-04-03 00:00:00
Creation Date	2001-05-03 07:56:05
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Document Title	Chapter 2

100 Watt High Band VHF Transmitter
Chapter 2, System Description
Chapter 2
System Description
The 420A is a complete 100 watt high
band VHF solid-state internally diplexed
television transmitter that operates at a
nominal visual output power of 100 watts
peak sync and an average aural output
power of 10 watts at a 10 dB A/V
ratio,10% sound.
The 420A has been submitted for type
acceptance to the FCC; the relevant FCC
identifier for the 420A is
_________________.
2.1 420A System Overview
The 420A (1066428) consists of (A1) a
100-watt, high-band VHF
exciter/amplifier tray (1066308) and (A2)
a bandpass filter assembly.
The exciter/modulator section of the 100watt, high-band VHF exciter/amplifier
tray operates using either baseband
audio and video inputs. However, if the
(optional) 4.5 MHz composite input kit
(1273-1128) is purchased, the 4.5 MHz
composite input or the baseband video
and audio inputs are used to produce a
diplexed, modulated, on-channel
frequency visual + aural RF output. The
switching between the 4.5 MHz
generated by the baseband inputs or by
the 4.5 MHz composite input is
accomplished by a relay, on the sync tip
clamp modulator board. The relay is
controlled by a baseband select which
connects to J18-6 and 7 on the rear of
the tray. To operate the transmitter with
the (optional) 4.5 MHz composite input
kit using baseband inputs, the baseband
video must be connected to J1 or J2, the
baseband audio must be connected to
the proper input jack, and a baseband
select must be connected to J18-6 and 7.
To operate the transmitter with the
(optional) 4.5 MHz composite input kit
using the 4.5 MHz composite input, the
4.5 MHz composite input must be
420A, Rev. 0
connected to J1 or J2 and the baseband
select must be removed from J18-6 and
7.
The exciter/modulator section of the tray
takes the baseband audio and video
inputs, or the (optional) 4.5 MHz
composite input, and produces a
combined 45.75 MHz + 41.25 MHz IF
output that connects to J32 on the ALC
board. The combined IF output of the
ALC board connects to the
mixer/amplifier assembly where it is
upconverted and filtered to the onchannel frequency visual + aural RF
output. The RF is filtered and amplified in
the amplifier section to the 100-watt
output power level. The RF output is
filtered in the bandpass filter assembly
and fed to the antenna via the
transmission line.
The exciter and upconverter section of
the tray operate when the circuit breaker
CB1 is on, but the amplifier section only
operates when the transmitter is in
Operate. This occurs because the
switching power supply that supplies the
operating voltages to the amplifier
section has an inhibit command applied
to it, shutting it off as long as the
transmitter is in Standby.
2.1.1 Exciter Section
The baseband video and audio inputs to
the transmitter connect to the rear panel
of the tray. The baseband video or the
(optional) 4.5 MHz composite input
connects to jack (J2), which is a loopthrough connected to jack (J1). By
removing the termination jumper on the
sync tip clamp/modulator board, jack
(J1) can be used as a connection for the
baseband video or the 4.5 MHz
composite input to another transmitter.
The baseband audio input connects to
the terminal block (TB1) for balanced
2-1
100 Watt High Band VHF Transmitter
audio or to the BNC jack (J3) for
composite audio, which is a loop-through
connected to jack (J13). There are also
connections for the remote monitoring
and operation of the transmitter at the
"D"-connector jacks (J10 and J11).
The baseband audio connects to (A4) the
aural IF synthesizer board (1265-1303),
in the exciter section, which provides the
amplification for each of the three
possible audio inputs and the amplifier
circuit that supplies the single audio
output. The board has the 4.5 MHz VCO
and the aural modulation circuitry that
produces the modulated 4.5 MHz output.
The board also contains a PLL circuit to
maintain the precise 4.5 MHz separation
between the aural (41.25 MHz) and
visual (45.75 MHz) IF frequencies. The
video input or 4.5 MHz composite input
to the exciter section connects to (A5)
the sync tip clamp/modulator board
(1265-1302) that takes the video input
and produces a sync tip clamped and
modulated visual IF + aural IF output at
the output jack J20. If the optional 4.5
MHz composite input is purchased, the
input is directed out of the sync tip
camp/modulator board to the (A24)
composite 4.5 MHz filter board (12271244) and the (A25) 4.5 MHz bandpass
filter board (1265-1307). These two
boards process the 4.5 MHz composite
input and produce the video that
connects back to the sync tip
clamp/modulator board at J27. The
clamp portion of the board maintains a
constant peak of sync level of the video
signal over varying average picture levels
(APL). The modulator portion of the
board contains the circuitry that
generates an amplitude-modulated,
vestigial-sideband IF signal output at
45.75 MHz.
Chapter 2, System Description
ALC board. The ALC board gives the
operator control over the output power
level of the transmitter by adjusting the
level of the combined IF signal. The IF
connects out of the board at J3 and is
directed to (A9) an IF phase corrector
board (1227-1250). The IF signal is
phase corrected as needed and fed back
to the ALC board.
2.1.2 Upconverter Section
The output of the ALC board (0 dBm)
connects to (A11-A1) the filter/mixer
board (1150-1102), in the (A11)
mixer/amplifier enclosure (1065007),
which takes the LO and heterodynes it
with the combined IF. This signal is then
fed to the high-band VHF filter/amplifier
board, high output (1064150), that
amplifies the RF signal and feeds it to the
(A23) high-band amplifier heatsink
assembly (1065008). The crystal
frequency needed to generate the LO is
produced by (A14-A1) the channel
oscillator board (1145-1201) in (A14) the
channel oscillator assembly (1145-1202).
The crystal frequency (+5 dBm) from the
oscillator is multiplied four times by
(A15-A1) the x4 multiplier board (11741112), in (A15) the multiplier enclosure
(1235-1101), which produces the LO
signal.
2.1.3 Amplifier Section
The 45.75 MHz is generated by (A7) the
IF oven oscillator board (1191-1404) and
connected (+5 dBm) to the sync tip
clamp/modulator board. The combined
visual IF + aural IF output (0 dBm)
connects to J32 on (A8) the ALC board
and then through relays to the rest of the
The RF output of the upconverter section
(+11 dBm) is fed to the amplifier section
of the transmitter. The amplifier section
consists of an (A23) amplifier heatsink
assembly (1065008) and associated
components. The first stage of the
amplifier section amplifies the RF to +31
dBm in (A23-A1) a high-band VHF
amplifier board assembly (1065812) that
consists of a high-band VHF amplifier
board (1218-1201) and associated
components. The RF is divided by the
(A23-A2) 2-way combiner assembly
(1064485) and fed to two parallel (A23A3 and A23-A4) high-band VHF amplifier
board assemblies (1065812). The
amplified signals are fed to another (A23-
420A, Rev. 0
2-2
100 Watt High Band VHF Transmitter
A5) 2-way combiner board. The RF
output from the 2-way combiner board
(+51 dBm) is fed through (A31) an
output coupler board (1088-1104) that
provides a forward power sample to
(A19) the visual/aural metering board
(1265-1309). A forward sample connects
to the transmitter control board that
supplies the voltage sample to the front
panel meter of the tray. The reject port
of the output coupler board provides the
reject sample to the visual/aural
metering board. The metering board
connects the reflected sample to the
transmitter control board for VSWR
cutback and front panel-reflected
metering for the tray.
Chapter 2, System Description
open the cover, remove the fuse
assembly, and reinsert it so that 230V is
visible with the cover closed.
The input AC voltage connects from the
jack (J14), which is part of (A1) the
power entry module on the rear of the
tray, to (CB1) a 10-amp circuit breaker
that is also on the rear of the tray. The
switched AC is wired through (A1) the
power entry module. This module
contains two fuses, one on each line, to
the terminal block (TB2). TB2 has four
MOVs mounted to the terminal block, one
connected from each leg of the input AC
to ground and one across each of the two
legs, for surge and transient voltage
protection of the tray.
2.1.4 Bandpass Filter Assembly
The output from the (A1) 100-watt, highband VHF exciter/amplifier tray is fed to
the input of the (A2) bandpass filter
assembly. The signal is fed to the (A2A1) 5-section bandpass filter with traps
and then through (A2-A2) a high-band
VHF coupler assembly that provides a
filtered RF sample for test purposes.
2.1.5 Operational Voltages
The transmitter needs an AC input of 115
or 230 VAC at 10 amps connected to it,
through the AC power plug, in order to
operate. The tray is set at the factory to
operate at the proper input voltage. This
is accomplished by setting the (A1)
power entry module to the correct line
voltage.
2.1.6 Configuration of the Power
Entry Module AC Input
The input AC is wired from TB2 to (A28)
the switching power supply and to (A2) a
toroid transformer. The (A28) switching
power supply (1063547) provides the
+48 VDC to operate the amplifier
assembles and also to (A10) the +48
VDC fan in the tray. The step-down
toroid (A2) supplies two 16 VAC outputs,
through the terminal block (TB2), to (A3)
the +12V(4A)/-12V(1A) power supply
board (1265-1312). The AC connects on
the board to two full-wave bridge
networks for +12 VDC and one full-wave
bridge network for -12 VDC. The rectified
DC from the +12 VDC full-wave bridge
networks is connected to the (U1-U4)
current limiting voltage regulator ICs.
The rectified DC from the -12 VDC fullwave bridge network is connected to the
(U5) current limiting voltage regulator
ICs. The ±12 VDC outputs connect to the
rest of the boards in the tray through
jacks (J3-J8).
For 115 volts, verify that 115V is
indicated on the rear panel cover on the
power entry module. If it is not, gently
open the cover, remove the fuse
assembly, and reinsert it so that 115V is
visible with the cover closed.
For 230 volts, verify that 230V is
indicated on the rear panel cover on the
power entry module. If it is not, gently
420A, Rev. 0
2-3
100 Watt High Band VHF Transmitter
2.1.7 Control and Status
Chapter 2, System Description
Meters, switches, and LED indicators are
mounted on (A17) the transmitter control
board (1068933). The control board is
attached to the back of the front panel to
allow for the switches and the LEDs to be
operated or viewed from the front of the
tray. The (S1) Operate/Standby switch
controls the output of the transmitter by
applying or removing the inhibit
command to the switching power supply
that provides the DC supply voltages to
the amplifier section.
transmitter by the presence of the video
input signal. When the switch is in
Automatic, the green LED (DS3) is lit
and, if the video input signal is lost, the
transmitter automatically switches to
Standby after a short delay. When the
video input signal returns, the
transmitter immediately switches back to
Operate. In Manual, the amber LED
(DS4) is lit and the operation of the
transmitter is controlled by the front
panel switches. During normal operation
of the transmitter, switch S2 should be in
the Auto position.
In Operate, the green LED (DS2) is on
and the inhibit command is removed.
When in Standby, the amber LED (DS1)
is on and the inhibit command is applied.
Switch (S2) is an Automatic/Manual
switch that controls the operation of the
The front panel of the tray also has LEDs
that indicate Video Fault (Loss) (red LED
[DS9]) and VSWR Cutback (amber LED
[DS7]). The meters, switches, and LEDs
found in the 420A are described in the
following tables.
420A, Rev. 0
2-4
100 Watt High Band VHF Transmitter
Chapter 2, System Description
Table 2-1. Meters
METER
METER (A18)
(mounted on the front panel)
SWITCH (S3), METER
(mounted on the front panel)
ALC
(0-1 V)
% EXCITER
(0-120)
% REFLECTED
(0-120)
% VISUAL POWER
(0-120)
% AURAL POWER
(0-120)
VIDEO
(0-1V)
AUDIO
(0-100kHz)
420A, Rev. 0
FUNCTION
Displays power in terms of a percentage of
the calibrated output power level. A fullscale reading is 120%. A reading of 100%
is equivalent to the full-rated peak of sync
visual output power, 100 watts. Also reads
% Exciter, % Reflected, and % Aural Power
along with the ALC voltage, video, and
audio levels.
Selects the desired % Power, ALC voltage,
video, or audio level reading
Displays the ALC voltage level (.85 VDC)
Displays the % Exciter Output power (level
needed to attain 100% output power)
Displays the % Reflected Output power
(<10%)
Displays the % Visual Output power of the
transmitter (100%=100 watts peak of
sync)
Displays the % Aural Output power of the
transmitter (100%=10 watts at 10 dB
A/V ratio)
Displays the video level (1V at white with
.3V sync only, -40 IRE)
Displays the audio level (±25 kHz balanced
or ±75 kHz composite); will not read if only
the 4.5 MHz composite input kit is used
2-5
100 Watt High Band VHF Transmitter
Chapter 2, System Description
Table 2-2. Switches (mounted on the front panel)
SWITCH
TRANSMITTER (S1)
OPERATE/STANDBY
MODE SELECT (S2)
AUTO/MANUAL
FUNCTION
The momentary contact switch (S1) applies
a ground to K1, latching relay, located 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, the
inhibit command is removed from the
switching power supply. This allows the
switching power supply to apply 48V to the
amplifier boards. When switched to
standby, the power supply is disabled.
The momentary contact switch (S2) applies
a ground to latching relay K2, on the
transmitter control board.
K2 will switch the transmitter to the
Automatic or Manual mode depending on
which direction S2 is pushed. In Automatic,
the video 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
video is lost, and will 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.
Table 2-3. Adjustments
ADJUSTMENT
GAIN (A20-R1)
420A, Rev. 0
DESCRIPTION
Adjusts the gain of the RF output using the
ALC board when the IF ALC circuit is
Enabled
2-6
100 Watt High Band VHF Transmitter
Chapter 2, System Description
Table 2-4. Control Indicators (LEDs mounted on the front panel)
INDICATOR
OPERATE (DS2 GREEN)
STANDBY (DS1 AMBER)
AUTO (DS3 GREEN)
MANUAL (DS4 AMBER)
FUNCTION
Indicates that the transmitter is in
Operate
Indicates that the transmitter is in
Standby
Indicates that the transmitter is in
Automatic mode; switches to Standby if the
input video signal is lost
Indicates that the transmitter is in Manual
mode; will not automatically switch to
Standby if the input video signal is lost
Table 2-5. Status Indicators (LEDs mounted on the front panel)
INDICATOR
VIDEO LOSS (DS9 RED)
VSWR CUTBACK (DS7 AMBER)
FUNCTION
Indicates that the input video has been lost
to the transmitter. The fault is generated
on the ALC board.
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.
Table 2-6. Samples (BNC connectors mounted on the front panel)
SAMPLE
f(s)
f(IF)
f(IC)
EXCITER O/P
2.1.8 Input and Remote Connections
DESCRIPTION
A sample of the channel oscillator output
taken from the sample jack of the channel
oscillator assembly. The (fC) channel
RF frequency equals four times
the crystal frequency (fS) minus the (fIF) IF
frequency.
A sample of the 45.75 MHz output from the
IF carrier oven oscillator board
A sample of the 4.5 MHz intercarrier
output from the aural IF synthesizer board
An output power sample of the exciter
taken from the VHF filter/amplifier board,
high output
The baseband video and audio inputs
alone or, if the (optional) 4.5 MHz
composite input kit (1273-1326) is
purchased, the 4.5 MHz composite input
or the baseband video input and audio
input to the transmitter, connect to the
rear of the tray. The baseband video
input, or the 4.5 MHz composite input,
connects to jacks J1 or J2, which are
loop-through connected. The baseband
audio input connects to TB1 for balanced
audio or to jacks J3 or J13, which are
420A, Rev. 0
2-7
100 Watt High Band VHF Transmitter
Chapter 2, System Description
loop-through connected, for composite,
stereo, audio. To use the 4.5 MHz
composite input kit, the baseband audio
can remain connected to the VHF exciter
even if the 4.5 MHz composite input kit is
used, but the baseband video must be
disconnected from J1 or J2 and the 4.5
MHz composite input connected to J1 or
J2. The baseband select command must
also be removed from J18-6 and 7.
remote connections are made to the
transmitter, they should be made
through the plug in J11 or to J10 in the
positions noted in Table 2-7.
Note: If the optional 4.5 MHz
composite input kit is purchased, the
baseband select connects to J18,
pins 6 and 7, on the back of the tray.
The remote interface connections for the
420A transmitter are listed in Table 2-7.
These connections are made to jack
(J11), the 37-position, "D"-connector, or
to jack (J10), the 25-position, "D"connector, on the rear panel of the tray.
Remote monitoring and operation of the
transmitter is provided through the jacks
(J10 and J11) on the rear of the tray.
Jack (J11) should have a dummy plug
connected to it, with a jumper connected
between pins 23 and 24, that provides
the interlock needed to operate the
transmitter. If this jumper is missing, the
transmitter will not switch to Operate. If
Note: Only the pins called out in
Table 2-7 are utilized in this
transmitter.
Table 2-7. Remote Interface Connections
FUNCTION
REMOTE JACK/PIN
NUMBER
Transmitter Enable Interlock
Transmitter Enable Interlock
Rtn
J11-24
INTERFACE TYPE
J11-24 and 23 must be
jumpered together for
normal operation; (11761038) jumper jack
should be used.
J11-23
Remote Control Commands
Transmitter Standby
(Disable)
Transmitter
Standby/Operate Rtn
Transmitter Operate
(Enable)
Transmitter Manual
Transmitter Auto/Manual
Rtn
Transmitter Auto
Power Level Raise (optional)
Pwr Lvl Raise/Lower Rtn
(optional)
Power Level Lower
(optional)
420A, Rev. 0
Contact closure
J11-22
J11-21
Contact closure
J11-20
J11-9
Contact closure
J11-36
J11-8
Contact closure
J10-11
Contact closure
J10-13
Contact closure
J10-12
2-8
100 Watt High Band VHF Transmitter
Chapter 2, System Description
Table 2-7. Remote Interface Connections
FUNCTION
Modulator Select (optional)
Modulator Select Rtn
(optional)
REMOTE JACK/PIN
NUMBER
J11-10
INTERFACE TYPE
Contact closure
J11-30
Remote Status Indications
Transmitter Operate
(Enable) Ind
Operate/Standby Ind Return
Transmitter Standby
(Disable) Ind
Transmitter Auto Indicator
Auto/Manual Indicator
Return
Transmitter Manual
Indicator
50 mA max. current sink
J10-3
J10-16
50 mA max. current sink
J10-4
J11-7
50 mA max. current sink
J11-32
50 mA max. current sink
J11-6
VSWR Cutback Indicator
VSWR Cutback Indicator
Return
J11-37
Video Loss (Fault) Indicator
Video Loss (Fault) Ind. Rtn
J11-25
J11-31
Receiver Fault (optional)
J11-12
50 mA max. current sink
J11-35
50 mA max. current sink
Remote Metering
Visual Output Power
Visual Output Power Rtn
J11-26
J11-28
1V full scale At 1kΩ
source resistance
Aural Output Power
Aural Output Power Rtn
J11-27
J11-29
1V full scale At 1kΩ
source resistance
Reflected Power
Power Rtn
J10-5
J10-22
1V full scale At 1kΩ
source resistance
Exciter Output Power
Power Rtn
J10-10
J10-22
1V full scale At 1kΩ
source resistance
420A, Rev. 0
2-9

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