User's Manual

2650 Watt VHF High Band Transmitter Chapter 5, Detailed Alignment Procedures
435B, Rev. 0 5-3
receiver tray is present in the
system). DS5 is always on with no
receiver.
The ALC is muted when the transmitter is
in Standby. To monitor the ALC, turn off
the two amplifier on/off circuit breakers
on the AC distribution assembly at the
rear of the cabinet and switch the
transmitter to Operate. Adjust the power
adjust gain pot on the front panel of the
VHF exciter tray to obtain +0.8 VDC on
the front panel meter in the ALC position.
On the ALC board (1265-1305), move
jumper W3 on J6 to the Manual position,
between pins 2 and 3, and adjust R87 on
the ALC board for +0.8 VDC on the front
panel meter in the ALC position. Move
jumper W3 back to Auto (between pins 1
and 2); this is the normal operating
position. The detected IF signal level at
J19-2 of the ALC board is connected to
the transmitter control board that
distributes the level to the two VHF
amplifier trays where it is used as a
reference for the automatic gain control
(AGC) in each amplifier tray.
5.1.4 VHF H.B. Exciter Tray Board
level Adjustments
5.1.4.1 (Optional) 4.5-MHz
Composite Input Kit
If the (optional) 4.5-MHz composite input
kit is purchased, the tray is capable of
operating by using either the 4.5-MHz
composite input or the baseband audio
and video inputs. The kit adds the (A24)
composite 4.5-MHz filter board (1227-
1244; Appendix D) and the (A25) 4.5-
MHz bandpass filter board (1265-1307;
Appendix D) to the transmitter. When
the 4.5 MHz intercarrier signal generated
by the 4.5 MHz composite input has been
selected by the 4.5 MHz composite input
kit, the 4.5-MHz generated by the aural
IF synthesizer board is not used. When
the 4.5 MHz intercarrier signal generated
by the baseband video and audio inputs
with baseband has been selected by the
4.5 MHz composite input kit, the
composite 4.5 MHz filter board and the
4.5 MHz bandpass filter board are not
used.
The tray has been factory tuned and
should not need any alignments to
achieve normal operation. To align the
tray for the 4.5 MHz composite input,
apply the 4.5 MHz composite input, with
the test signals used as needed, to the
video input jack (J1 or J2 [loop-through
connections]) on the rear of the tray.
Select the 4.5 MHz composite input by
removing the baseband select from J7-6
and J7-7 on the rear of the tray.
To align the exciter using baseband video
and audio inputs, apply the baseband
video, with the test signals used as
needed, to the video input jack (J2) and
the baseband audio to the proper
baseband audio input on the A/V input &
remote interface panel. For balanced
audio input, connect TB1-1(+), TB1-
2(grnd), and TB1-3 (-). For
composite/stereo audio, connect the
composite audio input jack (J6). Connect
a baseband select from J7-6 and J7-7 on
the rear of the exciter tray.
5.1.4.1.1 (Optional) (A24) Composite
4.5-MHz Filter Board (1227-1244;
Appendix D)
This board is part of the 4.5-MHz input
kit and will only function properly with a
4.5-MHz composite input signal and the
4.5-MHz composite input selected. To
align this board:
1. Connect the test signal from an
envelope delay measurement set to
the video input of the tray at J1 or
J2.
2. Connect an oscilloscope to jack J7,
video out, between the J7 center
pin and pin 1 or 3 (ground). Adjust
C21, frequency response, if needed,
for the best frequency response.
Adjust R32, video gain, for a signal
level of 1 Vpk-pk on the
oscilloscope.