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15-10
Diagnostics Theory
RF_DIAGS
Down Converters (With Spectrum Analyzer) Test
The RF generator is fed to the receiver IF through the A23 Input and A11 Receiver Mixer
assemblies to the second mixer in the receiver. The signal is measured by the spectrum
analyzer at three frequencies at the SA_114.3M output.
IF Counter Test
The signal is measured again after the third mixer and FM discriminator at the IF_CNT
output by the counter.
AGC Open Loop (At AM Output) Test
The AGC open loop operation is checked at both high and low levels at three DAC level
settings. The signal is measured after the pulse detector at the DEMOD_AUD output. This
DC level represents the IF level.
AGC Closed Loop (At AM Output) Test
The AGC loop is closed and the level at the DEMOD_AUD output is measured again with
both AM and Pulse selected.
AGC Reference DAC Test
The AGC loop is opened and the closed loop level DAC is measured by the voltmeter at
the AUX7_VM output.
AGC Open-Loop Drive DAC Test
The AGC loop is opened and the open loop level DAC is measured by the voltmeter at the
AUX7_VM output.
Temperature Test
The temperature sensor is measured by the voltmeter at the AUX7_VM output.
AM Demodulator Test
The AUDIO OUT source is routed to the MODULATION IN AM/SPEECH connector
externally to produce an AM signal and the demodulated AM is measured at the
DEMOD_AUD output by the voltmeter through the A3 Audio Analyzer 1 assembly.
FM Demodulator Test
The FM demodulator is measured statically by changing the RF generator frequency by a
small amount and measuring the DC voltage change at the output of the FM demodulator
at the DEMOD_AUD output by the voltmeter through the A3 Audio Analyzer 1 assembly.