Exciter Interface (A2J4)
Jack – Pin #
Function
2
6
33
J3 – 5
VIDEO SENSE: A high or low indication for the presence or absence of video
programming is delivered to this output from the Video Detector Switch (VDS)
TALLY jack via J8-1. With video present at INPUT A9-A of the VDS, an open
is sent from A9J1-NO to J8-1 and is looped to J3-5 placing a high on the
Exciter’s Control/Interface input A2PC4J4-5 and gate A2PC4U2C-10. If a loss
of video occurs, a ground appears at A9J1-NO forcing A2PC4U2C low at pins
10 & 8. This low appears at AMP BIAS CONTROL input J3-3 from A2PC4J4-3
deactivating power supplies A3PS1/PS2 in the 500W UHF Power Amplifier.
J3 – 3
AMP BIAS CONTROL: This control voltage is generated on the Exciter’s
Control/Interface board (A2PC4) and forwarded to this input pin from
A2PC4J4-3. Its purpose is to activate or deactivate the power supplies (A3PS1/
PS2) contained within the 500W UHF Power Amplifier drawer A3. Power supply
activation requires a high at U3-2 which will appear when the Exciter’s UHF
Synthesizer A2A2 is locked (A2PC4U1A high), when the OPERATE/STANDBY
switch A2PC3S1 is in OPERATE (A2PC4U1D-11 high) and when the VIDEO
SENSE line A9J1-NO is high (A2PC4U2C high) indicating video present at the
modulator. The resulting low output at U3-1 will back bias switching transistors
Q1A/B and Q2A/B providing an open/high to the Power Supply/Thermal
Interface board A3PC2 turning on power supplies A3PS1/PS2 in the 500W
Power Amplifier drawer. If any of the above conditions change creating a logic
low at J3-3, then the 500W UHF Power Amplifier will be shut down.
J3 – 8
GND: From A2J4-8
Audio/Video/Remote Panel Interface (A8J1)
Jack – Pin #
Function
J4 – 1
REFLECTED POWER: This voltage, proportional to the reflected power seen
at the output of the transmitter, is provided for monitoring at REMOTE plug
A8J1-1 on the rear Video/Audio/Remote panel. The voltage is taken from output
pin 7 of meter adjust amplifier U5B which is primarily used to drive the RF
POWER meter DS5/DS6/DS7 mounted on the Control/Metering front panel via
FWD/REFL switch S1. The gain of U5B is controlled by the setting of poten-
tiometer R32 and receives its reflected power voltage from Metering Detector
output A7A1J3-1 via REFLECTED POWER INPUT J6-1. With S1 in the REFL
position, the information supplied by U5B is fed from S1-2 & 1 to four quadrant
multiplier U10 which squares the voltage so that the bar graph will respond as a
power meter rather than a volt meter. The signal is then amplified by U6A
before distribution to bar graph drivers U7/U8/U9. With the TTU500FA trans-
mitter operating at its rated power and REFLECTED POWER LED DS9 lit, REFL
METER ADJUST R32, accessible through the Control/Metering panel, is
adjusted for a 100% indication on the RF POWER meter with a simulated open
at the transmitter’s output (total output power returned).
J4 – 3
FWD POWER: This voltage, presented at the Video/Audio/Remote panel
REMOTE plug A8J1-3 for monitoring, is proportional to forward power produced
at the transmitter’s output. The voltage is generated at meter adjust op-amp
U5A-1 which receives its input from Metering Detector A7A1-5 through