User's Manual

Digital UHF Transmitter Chapter 4, Circuit Descriptions
DT835A, Rev. 1 4-18
transmitter, as needed, to maintain a
maximum of 20% VSWR. An interlock
(low) must be present at J8-24 for the
transmitter to be switched to Operate
and, when the interlock is present, the
green Interlock LED DS5 will be lit.
4.3.10.1 Operate/Standby Switch
K1 is a magnetic latching relay that
controls the switching of the
transmitter from Operate and Standby.
When the Operate/Standby switch S1
on the front panel of the tray is
switched to Operate, one coil of relay
K1 energizes; this causes the contacts
to close and apply a low to U4B-9. If
the transmitter interlock is present, and
there are no overtemperature faults,
lows will also be applied to U4B-10,
U4B-11, and U4B-12. With all the
inputs to U4B low, the output at U4B-
13 will be low. This low biases off Q1,
which turns off the amber Standby LED
DS1 on the front panel, and applies a
high to Q2. The high turns on and lights
the green Operate LED DS2 also on the
front panel. When Q2 is biased on, it
connects a low to Q12, which biases it
off, and allows the ALC to be applied to
J1, which is connected to any external
amplifier trays. The low from U4B-13 is
also applied to Q4 and Q24, which are
biased off, and removes the disables
from J1-4 and J18-1. The low from
U4B-13 also connects to Q10, which is
biased on, connects a high to Q6, Q7,
Q8, and Q9, which are also biased on,
and applies -12 VDC enables at J8-2, 3,
4, and 5, which connect to any external
amplifier trays. The high applied to Q2
is also connected to Q5 and Q26, which
are biased on, and applies a low enable
to J1-3, which can connect to a remote
operate indicator. The transmitter is
now in Operate.
When the Operate/Standby switch S1 is
switched to Standby, the other coil of
relay K1 energizes, which causes the
contacts to open. A high, +12 VDC, is
applied to U4B-9. The high at the input
causes the output at U4B-13 to go
high. The high biases on Q1, which
applies a low to the amber Standby
LED DS1 on the front panel and turns it
on. Q1 also applies a low to Q2, which
turns off and extinguishes the green
Operate LED DS2. In addition, Q12 is
biased on and connects to U2C, whose
output goes low and pulls the ALC
voltages at J1 low, lowering the gain of
the external amplifier trays. The high
from U4B-13 is applied to Q4 and Q24,
which are biased on, and applies
disables at J1-4 and J18-1. The high
from U4B-13 also connects to Q10,
which is biased off. When Q10 is off, it
removes the high from Q6, Q7, Q8, and
Q9, which are biased off, and removes
the -12 VDC enables at J8-2, 3, 4, and
5 that connect to the external amplifier
trays. The low applied to Q2 is also
connected to Q5 and Q26, which are
biased off, and removes the remote
enable at J1-3. The transmitter is now
in Standby.
4.3.10.2 Automatic/Manual Switch
K2 is a magnetic latching relay that
switches the operation of the
transmitter to Automatic or Manual
using Auto/Manual switch S2 on the
front panel of the tray.
When the S2 switch is set to the Auto
position, the operation of the
transmitter is controlled by the fault
circuits and will stay in Operate even if
Operate/Standby switch S1 is switched
to Standby.
With switch S2 in Auto, a low is applied
to one coil in the relay that energizes
and closes the contacts. The closed
contacts apply a low to the green
Automatic LED DS3, causing it to light.
The low from the relay connects to
U5A, pin 2; U5D, pin 13; Q21; and
Q23. Q21 and Q23 are biased off,
which causes their outputs to go high.
The high from Q21 connects to the
amber Manual LED DS4 on the front
panel, biasing it off, and to Q22,
biasing it on. The drain of Q22 goes