Assembly Instructions Chapter 4

4-6 kW UHF Translator Chapter 4, Circuit Descriptions
837B, Rev. 0 4-24
on J10, the base of Q16 goes high. The
red Video Loss Fault LED DS9 on the
front panel will be extinguished. Q16 is
biased on, which causes its drain to go
low. The low is wired to U5B, pin 5;
U5B, pin 6, will be low if no ALC fault
occurs. The two lows at the inputs
make the output at U5B, pin 4, go high.
The high is wired to Q18, which is
biased on, causing the drain to go low.
The low is connected to U3D, pin 12,
which causes its output at U3D, pin 14,
to go low. The low connects to U5A, pin
1, and, if the translator is in Auto, pin 2
of U5A is also low. With both inputs
low, the output of U5A at pin 3 goes
high. The high forward biases Q20 and
causes its drain to go low. The low
connects to the operate coil on relay K1
that switches the translator to Operate.
The low at U5C, pins 8 and 9, causes
its output at pin 10 to go high. This
high is connected to U5D, pin 12, and,
if the translator is in Auto, pin 13 of
U5D is low. The high on pin 12 causes
the output of U5D to go low and
reverse bias Q19. The drain of Q19
goes high and this removes the low
from the standby coil in relay K1.
Overtemperature Fault
The (A8-A1) thermal switch on the (A8)
output reject load connects to J8-1 on
the board. If the temperature of the
thermal switch raises above 170° F, it
closes and applies a low to J8-1. The
low connects to Q3, which is biased off,
and to the red Overtemperature LED
DS6, which is biased on. The drain of
Q3 goes high and connects to pins 11
and 12 of U4B. The high at the input to
U4B causes it to go high and switches
the system to Standby; this removes
the Operate Enable commands to the
external amplifier trays and also to the
(Optional) External Exhaust Kits.
VSWR Cutback Fault
The reflected power sample of the RF
output of the translator is connected to
J2, pin 9, on the translator control
board. The sample connects to op-amp
U1B, pin 5, which buffers the signal
before it is split. One of the split-
reflected samples connects to J1-5 on
the board; J1-5 is wired to J10-5 on the
rear of the tray for remote monitoring.
Another split-reflected sample connects
to position 3 on the front panel meter
for the tray. The final split remote-
reflected sample connects to U2B, pin
5.
If the reflected sample level increases
above the level set by R22, the VSWR
cutback pot, the output of U2B at pin 7,
goes high. The high is connected to
Q11 through CR11, which is biased on,
making U2C, pin 10, low and causing
U2C, pin 8, to go low. This low is split
and fed out of the tray at J1-6, J1-7,
J1-8, and J1-9. These are ALC outputs
to the amplifier tray that cut back the
output power of the amplifier tray. The
low from U2C, pin 8, is also fed through
coaxial jumper W2 on J13 and J14 to
R73. R73 is a bias-adjust pot that sets
the level of the pin attenuator bias that
is available as an output at J16. The
high at U2B, pin 7, is also fed to the
base of Q14 and Q13, which are
forward biased. This produces a low at
the drains that connect to the front
panel amber VSWR Cutback LED DS7,
causing it to light and indicate that the
tray is in cutback, and to output jack
J8-37 for the connection to a remote
VSWR cutback indicator.
Receiver ALC Fault
A sample of the ALC voltage from the
Receiver tray is connected to J8-11 on
the transmitter control board. If the
receiver is operating normally, the ALC
level that is applied to U3C, pin 9,
remains below the trip level set by
R35; as a result, the output at pin 13
stays high. The high is applied to the
red ALC Fault LED DS8, which is off.
The high also connects to U3A, pin 2,
and to Q15. Q15 is biased on and the
drain goes low. The low connects to
U5B, pin 6. In addition, U5B normally