Assembly Instructions Chapter 4

4-6 kW UHF Translator Chapter 4, Circuit Descriptions
837B, Rev. 0 4-11
MHz is then connected to J7 and, if
jumper W3 is between pins 1 and 2,
the 4.5-MHz signal from the external
source is connected to the mixer. Mixer
Z2 heterodynes the aural-modulated,
4.5-MHz signal with the 45.75-MHz CW
signal to produce the modulated 41.25-
MHz aural IF signal.
The output of the mixer is fed to a
bandpass filter that is tuned to pass
only the modulated 41.25-MHz aural IF
signal that is fed to jack J16, the
41.25-MHz loop-through out jack of the
board.
For normal operation, the 41.25-MHz
signal is jumpered by a coaxial cable
from J16 to J17 on the board. If the
(optional) aural IF loop-through kit is
purchased, the 41.25-MHz signal is
connected to the rear of the tray, to
which any processing trays can be
connected, and then back to jack J17
on the board. The modulated 41.25-
MHz aural IF signal from J17 is
connected through amplifier ICs U15
and U16. The amplified output is
connected to the attenuator-matching
circuit that is adjusted by R85. R85
increases or decreases the level of the
41.25 MHz that sets the A/V ratio for
the diplexer circuit. The diplexer circuit
takes the modulated 45.75-MHz visual
IF and the modulated aural IF and
combines them to produce the 45.75-
MHz + 41.25-MHz IF output. The
combined 45.75-MHz + 41.25-MHz IF
signal is amplified by U12 and
connected to combined IF output jack
J20 on the board. A sample of the
combined IF output is provided at J21
on the board. If a NICAM input is used,
it connects to J36 on the board. The
level of the NICAM signal is set by R109
before it is fed to the diplexer circuit
consisting of L28, L29, and R115. This
circuit combines the NICAM signal with
the 45.75-MHz visual IF + 41.25-MHz
aural IF signal.
4.2.2.6 Operational Voltages
The +12 VDC needed to operate the
translator control board enters the
board at J23, pin 3, and is filtered by
L26, L33, and C73 before it is fed to
the rest of the board.
The -12 VDC needed to operate the
board enters the board at J23, pin 5,
and is filtered by L27 and C74 before
being fed to the rest of the board.
4.2.3 (A6) (Optional) Delay
Equalizer Board (1227-1204;
Appendix D)
The optional delay equalizer board
provides a delay to the video signal,
correction to the frequency response,
and amplification of the video signal.
The video signal enters the board at J1-
2 and is connected to a pi-type, low-
pass filter consisting of C16, L7, and
C17. This filter prevents any unwanted
higher frequencies from entering the
board. The output of the filter is
connected to amplifier stage U1; the
gain is controlled by R29. The video
output of the amplifier stage is wired to
the first of four delay-equalizing circuits
that shape the video signal to the FCC
specification for delay equalization or to
the shape needed for the system. The
board has been factory-adjusted to this
FCC specification and should not be
readjusted without the proper
equipment.
Resistors R7, R12, R17, and R22 adjust
the sharpness of the response curve
while inductors L1, L2, L3, and L4
adjust the position of the curve. With a
delay equalizer test generator signal or
a sine x/x video test pattern input, the
resistors and inductors can be
adjusted, while monitoring a Tektronix
VM700 test measurement set, until the
desired FCC delay equalization curve or
system curve is attained. The delay-
equalized video signal is connected to
J1-4, the video output of the board. A