Assembly Instructions Chapter 4

4-6 kW UHF Translator Chapter 4, Circuit Descriptions
837B, Rev. 0 4-21
After the signal is amplified by U5, it is
applied to a second stage through T5.
The transformer doubles the voltage
swing by means of a 1:4 impedance
transformation. Resistors R39, R57,
R58, and R40 form an L-pad that
lowers the level of the signal. The
signal is applied to amplifier U6 to
compensate for the loss in level
through the L-pad. After the signal is
amplified by U6, it is applied to a third
stage through T6. The transformer
doubles the voltage swing by means of
a 1:4 impedance transformation.
Resistors R42, R59, R60, and R43 form
an L-pad to lower the level of the
signal. The signal is applied to amplifier
U7 to compensate for the loss in level
through the L-pad. TP1 is a test point
that gives the operator a place to
measure the level of the in-phase IF
signal that is connected to mixer stage
Z2. The amplitude corrector can be
disabled by moving jumper W3 on J10
to the Disable position; this will move
the breakpoint past sync tip and will
have no effect on the signal.
4.2.6.3 Output Circuit
The phase-corrected signal from pin 1
on combiner Z2 exits the board at IF
output jack J4 after passing through a
matching network consisting of six
resistors.
4.2.7 (A17) Transmitter Control
Board (1245-1101; Appendix D)
The transmitter control board provides
information on system control functions
and the operational LED indications;
these can be viewed on the front panel
of the translator. The main control
functions are for the Operate/Standby
and Auto/Manual selections. When the
translator is switched to Operate, the
board supplies the enables to any
external amplifier trays. The board also
performs the automatic switching of the
translator to Standby upon the loss of
the video input when the translator is
in Auto.
The transmitter control board contains
a VSWR cutback circuit. If the VSWR of
the translator increases above 20%,
the VSWR cutback circuit will become
active and cut back the output level of
the translator, as needed, to maintain a
maximum of 20% VSWR. An interlock
(low) must be present at J8-24 for the
translator to be switched to Operate.
When the interlock is present, the
green Interlock LED DS5 will be lit.
4.2.7.1 Operate/Standby Switch S1
K1 is a magnetic latching relay that
controls the switching of the translator
from Operate to Standby. When
Operate/Standby switch S1, on the
front panel of the tray, is moved to
Operate, one coil of relay K1 energizes
and causes the contacts to close and
apply a low to U4B-9. If the translator
interlock is present, and there is no
overtemperature fault, lows will also be
applied to U4B-10, U4B-11, and U4B-
12.
With all of the low inputs to U4B, the
output at U4B-13 will be low. The low
biases off Q1 and this turns off the
amber Standby LED DS1 on the front
panel. In addition, this action applies a
high to Q2 and 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 and biases it off;
this allows the ALC to be applied to J1
and connect 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, and connects a high to Q6,
Q7, Q8, and Q9; these are biased on
and apply -12 VDC enables to J8-2, J8-
3, J8-4, and J8-5, which connect to any
external amplifier trays. The high
applied to Q2 is also connected to Q5
and Q26, which are biased on, and
apply a low enable to J1-3, which
connects to a remote operate indicator.