User's Manual

3300-Watt VHF Low Band Transmitter Chapter 2, System Description,
Maintenance & Remote Control Connections
335B, Rev. 0 2-2
modulated 4.5 MHz IF, from the aural IF
synthesizer board, is mixed with the
45.75 MHz CW to produce a modulated
41.25 MHz aural IF output. The video
modulated 45.75 MHz is then diplexed
with the audio modulated 41.25 MHz to
produce the combined Visual IF + Aural
IF output of the board that connects to
the ALC board.
4.5 MHz Composite Input Kit
NOTE: If your transmitter does not
contain the 4.5 MHz composite input kit,
the following paragraph description does
not pertain. If the (optional) 4.5-MHz
composite input kit is purchased, the 4.5-
MHz composite input or the baseband
video and audio inputs are used. The
switching between the inputs is
accomplished by a relay mounted on the
sync tip clamp modulator board that is
controlled by a baseband select. The
baseband select controls a relay that
selects either the 4.5 MHz generated
from the baseband inputs or from the
4.5-MHz composite input. To operate the
transmitter with the (optional) 4.5-MHz
composite input kit using baseband
inputs, the baseband video must be
connected to J1 or J2, the baseband
audio must be connected to the proper
input jack, and a baseband select must
be connected from J7-6 and J7-7. To
operate the transmitter with the
(optional) 4.5-MHz composite input kit
using the 4.5-MHz composite input, the
4.5-MHz composite input must be
connected to J1 or J2 and the baseband
select must be removed from J7-6 and
J7-7.
IF Carrier Oven Oscillator Board
NOTE: If the precise frequency kit is
present in your transmitter, the IF VCXO
Board (1248-1131) will be used.
The IF carrier oven oscillator (1191-
1404) or the IF VCXO board generates
the 45.75 MHz visual IF CW signal that
connects to the sync tip clamp/modulator
board.
ALC Board
The (A8) automatic level control (ALC)
board (1265-1305) provides the ALC and
amplitude linearity correction of the
45.75 MHz + 41.25 MHz IF signal. The
ALC circuit adjusts the level of the
combined IF signal through the board
that controls the output power of the
transmitter. The level controlled
combined IF output of the ALC board
connects to the filter/mixer board.
VHF L.B. Filter/Mixer Board
The (A11-A2) VHF filter/mixer board
(1153-1101) is made up of three
separate circuits. The on channel
frequency RF output of the x2 multiplier
board connects to a filter and amplifier
circuit before it is connected to the mixer
stage. The combined 41.25 MHz + 45.75
MHz IF from the ALC board also connects
to the mixer stage. The RF output of the
mixer is filtered and amplified in the final
circuit before it is connected to the VHF
filter amplifier board.
X2 Multiplier Board
The (A11-A1) x2 multiplier board (1172-
1111) multiplies the frequency of the RF
from the channel oscillator by a factor of
two using a broadband frequency doubler
circuit. The RF on channel frequency
output of the board connects to the
filter/mixer board.
VHF Low Band Filter Amplifier Board
The VHF low band filter/amplifier board
(1064251) is made up of two separate
circuits. The RF output of the filter/mixer
board is connected to a filter circuit tuned
for best response on the channel
frequency. The filtered RF is then
connected to an amplifier circuit with a
manual gain control. The output of the
board connects to J15, the RF output jack
located on the rear of the VHF exciter
tray