User's Manual

3300-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions
335B, Rev. 0 4-20
standby indicator, if present, and J18-1.
The low from U4B-13 also connects to
Q10, which is biased on, and connects a
high to Q6, Q7, Q8, and Q9, which are
biased on and apply -12 VDC enables to
J8-2, J8-3, J8-4, and J8-5 that connect to
the VHF amplifier trays. The high applied
to Q2 is also connected to Q5, which is
biased on, and applies a low enable to
J1-3, which connects to the remote
operate indicator, if present, turning it
on. The transmitter is now in the
Operate mode.
When the Operate/Standby switch S1 is
moved to Standby, the coil connected to
pins 1 and 6, of relay K1 energizes,
causing the contacts to open and a high,
+12 VDC, to be 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,
that turns on. The low is also applied to
Q2, which causes Q2 to turn off and
extinguishes the green Operate LED DS2.
The low from Q2 connects to Q12 that is
biased on, which causes the output from
U2C to go low that pulls the ALC voltages
at J1 low. This lowers the gain of the
external VHF amplifier trays. The high
from U4B-13 is applied to Q4 and Q24,
which are biased on, and applies a
disable at J1-4, which connects to the
remote standby indicator, if present, and
to J18-1, power supply disable, which is
not used in the 335B. The high from
U4B-13 connects to the base of Q10,
which is biased off. Q10 biased off
removes the high from Q6, Q7, Q8, and
Q9, which are biased off, and removes
the -12 VDC enables at J8-2, J8-3, J8-4,
and J8-5, which connect to the external
VHF amplifier trays, turning off the power
supplies in the trays. The low applied to
Q2 is also connected to Q5, which is
biased off, and removes the remote
enable at J1-3, which connects to the
remote operate indicator, if present,
turning it off. The transmitter is now in
the Standby mode.
4.1.8.2 Automatic/Manual Switch S2
K2 is a magnetic latching relay that
switches the operation of the transmitter
to Automatic or Manual using the
Auto/Manual switch S2 mounted on the
front panel of the VHF exciter tray.
When S2 is set to the Auto position, the
operation of the transmitter is controlled
by the fault circuits and will stay in
Operate even if the Operate/Standby
switch S1 is moved to Standby, as long
as no fault occurs. With S2 in Auto, a
low is applied to the coil connected to
pins 3 and 4, in the relay and this
energizes and closes the contacts. The
closed contacts apply a low to the green
Automatic LED DS3, which will light. The
low from the relay connects to U5A pin 2,
U5D pin 13, Q21, and Q23. The low to
Q21 and Q23 causes them to be 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 also to Q22,
biasing it on. The drain of Q22 goes low
and is applied to J8-7 that enables any
remote auto indicator. The low to Q23
biases it off and removes the enable to
J8-6 and any remote manual indicator.
When 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 S2 in Manual, a low is applied to the
coil connected to pins 1 and 6 in the
relay that energizes and opens the
contacts. The open contacts remove the
low from the green Automatic LED DS3
on the front panel that causes it to not
light. The high connects to U5A pin 2,
U5D pin 13, Q21, and Q23. Q21 and 23
are biased on that causes 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 and is
applied to J8-7, which will disable any
remote auto indicators. Q23 is biased on
and applies a low to J8-6, which will
enable any remote manual indicators.