User's Manual

3300-Watt VHF Low Band Transmitter Chapter 4, Circuit Descriptions
335B, Rev. 0 4-30
shifter board, the (A2-A2) filter/amplifier
board and the (A3-A2) overdrive
protection board.
The fuses F1, F2 and F3 are 20-amp
fuses. F4 is a 5-amp fuse, F6 is a 2-amp
fuse, and F7 is a 1-amp fuse. F5 is not
used in this configuration. The 20 amp
fuse F1 protects +30 VDC to (A4-A1) one
of the low-band final amplifier pallet, the
20 amp fuse F2 protects (A4-A2) another
low-band final amplifier pallet and the 20
amp fuse F3 protects (A4-A3) the last
low-band final amplifier pallet. The 5
amp fuse F4 protects +30 VDC to (A3-
A1) the low-band VHF amplifier board.
The fuse F5 is not used in this
configuration. The 2 amp fuse F6
protects +30 VDC to (A2-A2) the
filter/amplifier board. The 1 amp Fuse F7
protects the +30 VDC connected to J8
pin 2, on (A13) the AGC control board.
On the AGC control board, the +30 VDC
is connected to the regulator IC U7 that
takes the +30 VDC and regulates it to a
+12 VDC output. The +12 VDC is used
for the operation of the AGC control
board. The +12 VDC from A13-J11-3 is
connected to the current metering board
at A8-TB1-5. The +12 VDC is jumpered
on TB1 from TB1-5 to TB1-6, which is
wired to the (A2-A1) phase shifter board,
the (A2-A2) filter/amplifier board, and
the (A3-A2) overdrive protection board.
The current metering board also supplies
sample outputs of the operating currents
of the amplifier devices in the tray to the
front panel current meter. The meter in
the (I
1
) position reads the current for the
(A4-A1) low-band final amplifier pallet,
the meter in the (I
2
) position reads the
current for (A4-A2) the low-band final
amplifier pallet and the meter in the (I
3
)
position reads the current for the (A4-A3)
low-band final amplifier pallet. The
meter in the (I
D
) position reads the
current for the (A3-A1) low-band VHF
amplifier board. To read the desired
current, place switch S1 to the Current
position, then place switch S2 to the
desired current measuring position.
These current readings can be used when
setting up the idling currents, no RF drive
applied, for the devices. The (I
1
, I
2
, and
I
3
) currents are each set for 1.8 amps,
while the (I
D)
current is set for 3 amps.
220 VAC Input
In the tray, the 220 VAC is applied
through jack J4 to terminal block TB1.
When CB1, the 15-amp, front panel-
mounted circuit breaker, is switched on,
the 220 VAC is distributed from TB1 to
(A11 and A12) two cooling fans, which
will begin to operate, and to (A10) the
switching power supply. There are four
surge suppressors on the AC input lines
for protection from transients or surges.
VR1 and VR2 are mounted on TB1,
between the AC lines and VR3 and VR4
are mounted at the input to the switching
power supply from each AC line to
ground.
Power Supply Enable
The (A10) switching power supply only
operates when the power supply enable
control line, jack J3 pins 9 and 10, on the
rear of the tray, is shorted and there is
no overtemperature fault. The enable is
supplied by the VHF exciter tray when
the transmitter is switched to Operate.
The enable is applied to J10 pins 10 and
9 on (A13) the AGC control board (1142-
1601), which, if there is no
overtemperature fault, connects the
enable from J10 pins 6 and 7 to J1-18
and J1-14 located on the switching power
supply assembly. The green Enable LED
DS2 on the front panel will light,
indicating that an enable is present. If
the transmitter is in Standby, or if an
overtemperature fault occurs, the AGC
control board will not enable the
switching power supply. As a result, the
+30 VDC will be removed from the
amplifier modules and the front panel
Enable and Module Status LEDs will not
be lit.