Assembly Instructions Chapter 4

10-kW UHF Transmitter with Chapter 4, Circuit
Feedforward Drive Descriptions
840A, Rev. 0 4-37
When the Exciter Test switch is in
Normal, with K4 energized, it applies a
low to CR13 and then to inverter U8E,
pin 11, whose output at pin 12 then goes
high. The high also forward biases Q26
and Q27 and lights DS14, the front
panel-mounted Normal LED connected to
J14, pins 8 and 6. The high input to
inverter U8B, pin 5, causes the output at
pin 4 to go low. The low is applied to Q28
to Q33, biasing them off and removing
the exciter test functions.
The exciter can be operated without
using the 10-kW amplifier by switching
the Normal/Exciter Test switch on the
front panel of the metering control panel
to the Exciter Test position. With the
switch in this position, K4 is de-energized
and a high is applied to diode CR13,
causing it to reverse bias. The high from
K4 is also applied to Q25, which forward
biases it and produces a low at pin 4 of
the K3 relay. The low at pin 4 de-
energizes the relay and produces a high
that is applied to diode CR12, causing it
to reverse bias. Both CR12 and CR13 are
reverse biased; as a result, a high from
+12 VDC and R61 is applied to pin 11 of
U8E and causes its output at pin 12 to go
low. The low connects to Q26 and Q27
and biases them off. The low is also
applied to inverter U8B, pin 5, whose
output at pin 4 goes high. The high
connects to Q28 to Q33, forward biases
them, applies a low to the exciter tray,
lights the Exciter Test LED, and sets up
the exciter to operate without the need
for the 10-kW amplifier.
The Auto/Manual Test switch S6 on the
front panel controls K1, the magnetic
latching relay, by connecting a low input
to the board at J2, pins 7 and 8, for
Manual or to J2, pins 4 and 3, for
Automatic. When the Test switch is
moved to the Auto position, a low is
applied to K1, pin 6, that energizes the
relay and applies a low to U7F, pin 14,
causing its output to go high. The high is
applied to Q5 and Q7, forward biasing
them, and produces a low at their drain.
The low lights the front panel Automatic
LED. With the Test switch in the Manual
position, a low is applied to K1, pin 4;
this de-energizes the relay and connects
a high from K1, pin 2, to Q6, forward
biasing it and producing a low at its
drain. The low lights the front panel-
mounted Manual LED DS4. The high
output of K1 is also applied to U7F, pin
14, whose output goes low. The low is
applied to Q5 and Q7, which reverse
biases them, and extinguishes the front
panel Automatic LED.
The board also supplies the option that
allows for the automatic switching of the
transmitter between a receiver tray or a
modulator tray that is used as the input
tray based on the presence of video to
the modulator or the receiver tray. A
receiver tray, a modulator tray, and an IF
relay, to switch between the two outputs,
must be present in the transmitter for
the automatic switching to take place.
For automatic switching, jumper W2 on
J17 must be in Auto, between pins 1 and
2. Jumper W1 on J18 determines which
tray will be in control. The modulator tray
will be in control if W1 is between pins 1
and 2.
If a modulator and a receiver tray are in
place, the jumpers are set as stated
above, and the video input to the
modulator is present, a high will be
present at J2, pin 11. The high connects
to inverter U7B, pin 5, whose output at
pin 4 goes low. The low turns off the red
Video Fault LED DS3. The high also
connects to timer U1A, pin 5, and directly
to NOR gate U5C, pin 9. The high at the
NOR gate produces a low output at U5C,
pin 10; this low is applied through
jumper W1 on J18 and jumper W2 on J17
to the bases of Q8 to Q11. Q8 to Q11 are
reversed biased and apply the disables to
the IF relay to keep the output of the
modulator tray connected to the input of
the upconverter tray. In addition,
because Q11 is biased off, Q12 to Q14
will have highs applied to their bases to
bias them on. DS5, the green Modulator
On LED, will be lit.