Assembly Instructions Chapter 4

4-6 kW UHF Translator Chapter 4, Circuit Descriptions
837B, Rev. 0 4-25
has a low that is connected to U5B, pin
5, and produces a high at output pin 4.
The high is wired to Q18, which is
biased on, and makes its drain low. The
low connects to U3D, pin 12, which,
because the level is below the preset,
causes the output at U3D, pin 14, to go
low. A low at this point indicates a no-
fault condition. The high that is
connected to U3A, pin 2, causes its
output to go low. The low is connected
to Q25, which is biased off. The low is
removed from J8-12, which will not
light any remote receiver fault indicator
that is connected to it.
If the receiver malfunctions, the ALC
level applied to U3C, pin 9, goes high.
This is above the level set by R35 and it
causes the output at pin 13 to go low.
The low is applied to the red ALC Fault
LED DS8, which lights. The low also
connects to U3A, pin 2, and to Q15.
Q15 is biased off and the drain goes
high. The high connects to U5B, pin 6,
and produces a low at output pin 4. The
low is wired to Q18, which is biased off,
and this makes its drain go high. The
high connects to U3D, pin 12 and,
because the level is above the preset,
the output at U3D, pin 14, goes high. A
high at this point indicates a fault
condition that switches the translator to
Standby. The low connected to U3A,
pin 2, causes its output to go high. The
high is connected to Q25, which is
biased on, and causes the drain to go
low. The low is connected to J8-12,
which can light any remote receiver
fault indicator that is connected to it.
4.2.7.5 Metering
The front panel meter connects to J3-1
(-) and J3-2 (+), the output of switch
S3, on the transmitter control board.
The front panel meter has seven
metering positions that are controlled
by S3: Audio, Video, % Aural Power, %
Visual Power, % Reflected Power,
% Exciter, and ALC. The video sample
connects to the board at J5-4 and is
connected through video calibration pot
R20 to position 6 on Front panel meter
switch S3. The audio sample enters the
board at J5-6 and is connected through
audio calibration pot R19 to position 7
on Front Panel Meter switch S3.
The reflected sample connects to the
board at J2-9 and is connected through
buffer amplifier U1B and 100-Ω resistor
R84 to position 3 on Front Panel Meter
switch S3. The visual sample connects
to the board at J2-5 and is connected
through buffer amplifier U1D and 100-
Ω resistor R86 to position 4 on Front
Panel Meter switch S3. The aural
sample connects to the board at J2-7
and is connected through buffer
amplifier U1C and 100-ohm resistor
R85 to position 5 on Front Panel Meter
switch S3. The exciter sample connects
to the board at J2-3 and is connected
through buffer amplifier U1A and 100-Ω
resistor R87 to position 2 on Front
Panel Meter switch S3. The ALC sample
connects to the board at J6-1 and is
connected through buffer amplifier
U2C, ALC calibration pot R15 (which
adjusts the output of U2A, pin 1), and
through 100-Ω resistor R18 to position
1 on Front Panel Meter Switch S3.
Typical readings on the meter are:
• Video = 1 Vpk-pk at white
• % Reflected = < 5%
• % Visual power = 100%
• % Aural power = 100%
• % Exciter = The level on the meter
needed to attain 100% output
power from the translator
Refer to the test data sheet for the
translator for the actual reading:
• ALC = .8 VDC
• Audio = ±25 kHz with a balanced
audio input or ±75 kHz with a
composite audio input
Samples are provided for the remote
metering of the exciter at J1-10, the
visual at J8-26, the aural at J8-27, and
the reflected at J1-5.