Specifications

Section J
Analog Input Board
J.1 Introduction
This section describes the Analog Input board. Topics include
Function, Location, Block Diagram Description, Detailed Cir-
cuit Description, Troubleshooting, and Removal/Replacement
and Oscilloscope plots of key points.
NOTE: Parts List for this board is in Section VII.
J.2 Function
The Analog Input board includes an audio input amplifier, power
control adjustments, circuits for optimizing audio performance,
and +230VDC current overload and monitoring. The output
signal from this board is an audio signal with a DC component,
which goes to the A/D Converter board. The DC component
determines the transmitter’s unmodulated or carrier power out-
put, and the audio component changes the instantaneous power
output.
J.3 Location
The Analog Input board is located in the center PA cabinet, on
the back of the front door. (SEE VIEW 13)
J.4 Oscilloscope Waveform Plots
Actual oscilloscope waveform plots of key troubleshooting
points are located at the end of this section. All plots were taken
at 100 kW with 100% 1 kHz modulation at 540 kHz carrier
frequency, unless otherwise noted.
J.5 Block Diagram Description
J.5.1 Audio Flow
The audio input signal passes through a Bessel filter to the
transformerless Balanced To Unbalanced Amplifier.
An (Audio + DC) Power Level Summer adds a negative DC
offset that sets the maximum unmodulated carrier power level.
A +230VDC power supply sample correction voltage is proc-
essed by the Correction Signal Processor and is sent to the
Correction/Overload Summing Amplifier to improve low fre-
quency distortion. This signal is added to the (Audio + DC) signal
in the Power Supply Correction circuit to correct for changes in
the power supply voltage in order to maintain a constant carrier
level.
Power Foldback is accomplished by a resistive attenuator which
will reduce the (Audio + DC) signal should the carrier level need
to be reduced due to VSWR or other faults.
Figure J-1. Analog Input Block Diagram
888-2339-002 J-1
WARNING: Disconnect primary power prior to servicing.