Instruction manual

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to about 5%, SCA subcarriers to 10%. Again, the 100% mark on the
meter should be read as 10% for these measurements.
Output
Pre-check
The initial portion of the output adjustment procedure is performed
under simulated “on-air” operating conditions. Feed typical program
material to the stereo generator via the processing system, but stereo
temporarily disconnected the generator from the exciter until the pre-
check verifies normal operation.
The processor, itself, should now indicate normal values of gain
reduction, including a minimum of 6dB peak limiting of program audio
peaks. Under this condition the 708 bargraph display will show
consistent left (L) and right (R) channel signal activity peaking at 0dB.
A display much in excess of 0dB indicates limiter overshoots and a
possible deficiency of the processing system in maintaining a consistent
output “ceiling.” Occasional overshoots up to +1dB or +2dB are to be
expected, but anything above these values is cause to question
processing effectiveness.
Temporarily set the front-panel COMPOSITE PROCESSING control
fully clockwise to the 3dB point. With typical program audio applied,
check bargraph metering of the composite multiplex output (MPX).
Peak modulation should remain within the limits shown:
Stereo program modulation only — 100%
Stereo program and RDS only — 105%
Stereo program and one SCA only — 110%
Stereo program, RDS and SCA — 115%
Stereo program and two SCAs — 120%
NOTE: MPX metering relates to the total composite output voltage
peak excursion before the OUTPUT LEVEL control, not the actual FM
carrier deviation. The 100% reference point represents a normal stereo
signal without subcarriers; actual measurements will reflect the
algebraic addition of any subcarriers.
OUTPUT LEVEL
Adjustment
PLEASE be certain that you understand operation of the station Mod-
Monitor, and that it is properly calibrated and connected to the correct
transmitter/exciter RF sample point. The remainder of this procedure
is performed “on-air.”
1. Turn the 708 OUTPUT LEVEL control fully counterclockwise and
connect the generator’s COMPOSITE OUTPUT to the input of the
exciter.
2. Turn off or disconnect any subcarrier inputs to the 708. With only
the stereo programming applied, advance the OUTPUT LEVEL
control for a Mod-Monitor indication of frequent 100%-modulation
peaks.
3. Back-down the OUTPUT LEVEL control slightly, so that the 100%
peak flasher(s) light only occasionally.