Assembly Instructions Chapter 4

10-kW UHF Transmitter with Chapter 4, Circuit
Feedforward Drive Descriptions
840A, Rev. 0 4-19
11, biases on Q19, which applies a low
enable to the Standby switch; this places
the transmitter in the Standby mode.
When the video is returned, J7-5 goes
high. The high is applied to Q16, which is
biased on, and to the red Video Fault LED
DS9, which is extinguished. The output of
Q16 goes low and connects to U5B, pin
5. If there is no receiver ALC fault, U5B,
pin 6, is also low, which causes the
output at pin 4 to go high. The high
connects to Q18, which is biased on,
causing the drain of Q18 to go low. The
low connects to U3D, pin 12, whose
output at pin 14 goes low. The low
connects to U5C, pins 8 and 9, which
causes its output at pin 10 to go high,
and to U5A, pin 1. With Auto/Manual
switch S2 in Auto, a low is applied to
U5A, pin 2, and to U5D, pin 13. With
U5A, pins 1 and 2, low, its output at pin
3 goes high. With pin 12 of U5D high,
the output of U5D at pin 11 goes low.
With U5A, pin 3, high, it biases on Q20,
which applies a pulldown enable to the
Operate switch. A low at U5D, pin 11,
biases off Q19, which removes any
pulldown to the Standby switch. The
transmitter is switched to Operate.
Faults
There are four possible faults that may
occur in the transmitter and are applied
to the transmitter control board: video
loss fault, VSWR cutback fault,
overtemperature fault, and ALC fault.
There will be no faults to the board
during normal transmitter operations.
The receiver ALC fault circuit will only
function if a receiver tray is part of the
system.
Video Loss Fault.
If a video loss occurs,
the transmitter, while in Auto, will go to
Standby after a few seconds, until the
video is returned; at that point it will
immediately revert to Operate. A video
loss fault applies a low from the ALC
board to the video fault input at J7-5 on
the board.
With jumper W1 in place on J10, the
video fault is connected to the red Video
Loss Fault LED DS9 and to Q16. The LED
DS9 on the front panel will light and Q16
will be biased off, causing its drain to go
high. The high is wired to U5B, pin 5,
whose output at U5B, pin 4, goes low.
The low is wired to Q18, which is biased
off; this causes the drain to go high. The
high is connected to U3D, pin 12, which
causes its output at U3D, pin 14, to go
high. The high connects to U5A, pin 1,
and, if the transmitter is in Auto, pin 2 of
U5A is low. With pin 1 high and pin 2
low, the output of U5A goes low and
reverse biases Q20, shutting it off. The
high at U5C, pins 8 and 9, causes its
output at pin 10 to go low. This low is
connected to U5D, pin 12, and, if the
transmitter is in Auto, pin 13 of U5D is
also low. The lows on pins 12 and 13
cause the output to go high, which
forward biases Q19. The drain of Q19
goes low and connects the coil in relay
K1, causing it to switch to Standby.
When the video returns, the video loss
fault is removed from the video fault
input at J7-5. With jumper W1 in place
on J10, the base of Q16 goes high. The
red Video Loss Fault LED DS9 on the
front panel will go out. Q16 is biased on,
causing its drain to go low. The low is
wired to U5B, pin 5, and 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 and causes 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 transmitter 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 transmitter to Operate.
The low at U5C, pins 8 and 9, causes the
output at pin 10 to go high. This high is
connected to U5D, pin 12, and, if the
transmitter is in Auto, pin 13 of U5D is
low. The high on pin 12 causes the