User's Manual

Digital UHF Transmitter Chapter 4, Circuit Descriptions
DT835A, Rev. 1 4-19
low. The low is applied to J8-7 and this
will enable any remote auto indicator
that is connected to it. The low to Q23
biases it off and removes the enable to
any remote manual indicator connected
to J8-6.
When switch S2 is set to the Manual
position, the operation of the
transmitter is no longer controlled by
the fault circuits; it is controlled by
Operate/ Standby switch S1. With
switch S2 in Manual, a low is applied to
the other coil in the relay, which
energizes and opens the contacts. The
open contacts remove the low from the
green Automatic LED DS3 on the front
panel, causing it to not light. The high
connects to U5A, pin 2; U5D, pin 13;
Q21; and Q23. Q21 and Q23 are biased
on, causing their outputs to go low. The
low from Q21 connects to the amber
Manual LED DS4 on the front panel,
biasing it on, and to Q22, biasing it off.
The drain of Q22 goes high. This high is
applied to J8-7 and will disable any
remote auto indicator that is connected
to it. Q23 is biased on and applies a low
enable to any remote manual indicator
connected to J8-6.
4.3.10.3 Automatic Control of the
Transmitter
The transmitter control board also
allows the transmitter to be turned on
and off by the presence of modulation
to the transmitter when the transmitter
is in Auto. When a modulation fault
occurs due to the loss of the
modulation input, J7-5 goes low. The
low is applied through W1 on J10 to
Q16, which is biased off, and to the red
Modulation Loss Fault LED DS9 on the
front panel, causing it to light. The
drain of Q16 goes high and connects to
U5B, pin 5, causing the output at pin 4
to go low. The low connects to Q18,
which is biased off, causing the drain of
Q18 to go high. The high connects to
U3D, pin 12, whose output at pin 14
goes high. The high connects to U5C,
pins 8 and 9, which causes its output at
pin 10 to go low, and to U5A, pin 1,
causing its output at pin 3 to go low.
With S2 set to Automatic, a low is
applied to U5A, pin 2, and to U5D, pin
13. When U5A, pin 1, is high and U5A,
pin 2, is low, it causes the output at pin
3 to go low. When U5D, pin 12, and
U5D, pin 13, are both low, it causes the
output to go high. When U5A, pin 3, is
low, it biases off Q20 and removes any
pull-down to the Operate switch. A high
at U5D, pin 11, biases on Q19 and
applies a low enable to the Standby
switch; this places the transmitter in
the Standby mode.
When the modulation input is returned,
J7-5 goes high. The high is applied to
Q16, which is biased on, and to the red
Modulation Fault LED DS9, which goes
out. 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. This high connects to Q18,
which is biased on, and causes 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 the
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, the output at pin 3 goes
high. With pin 12 of U5D high, the
output of U5D at pin 11 goes low.
When U5A, pin 3, is high, it biases on
Q20, which applies a pull-down enable
to the Operate switch. A low at U5D,
pin 11, biases off Q19, which removes
any pull-down to the Standby switch.
The transmitter is switched to Operate.
4.3.10.4 Faults
There are four possible faults that may
occur in the transmitter and are applied
to the board: modulation loss fault,
VSWR cutback fault, overtemperature
fault, and ALC fault. During normal
operations there are no faults to the
board. The receiver ALC fault circuit will