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2. Using a Spectrum Analyzer with a tracking generator align RF filters to have a
symmetrical response centered at 136.9 MHz when NAV/COMM unit is tuned to
136.9 MHz. Peak gain shall be 15 +/- 1.5 DB when output is measured at mixer input.
3. Apply –99 dbm at 136.9 MHz with 30% modulation. Peak the IF coil and adjust the
AGC pot for 6.0 volts on the AGC line. Adjust the Audio gain pot for 4.0 vp-p on
Audio Output.
NAV Receiver tuning:
1. Use the COMM Receiver procedure except use 117.9 MHz for the test channel.
F and G. NAV (Dwg. SS2714) and COMM (SS2716) Synthesizers
The NAV and COMM synthesizers are identical except for tuning and an additional
output is provided in the COMM synthesizer to drive the transmitter.
COMM Synthesizer tuning
1. Connect COMM Synthesizer to an operating NAV/COMM assembly and monitor
receiver and transmitter outputs with RF Voltmeter. Monitor Tuning voltage with a
DC Voltmeter and Transmitter output with a Sideband Monitoring system capable of
measuring 25 KHz sideband signals.
2. Set NAV/COMM assembly to 136.95 MHz in Receive mode. Adjust tuning voltage
with R8 to 10.0 vdc.
3. Verify a tuning voltage of about 6 vdc at 118.7 MHz.
4. Receiver RF output shall be 9.0 +/- 1 db.
5. Select transmit mode and Transmit RF shall be 9.0 +/- 2 db.
6. Adjust R7 to null 25 KHz sidebands on the Transmitter output.
NAV Synthesizer tuning
1. Connect NAV Synthesizer to NAV/COMM Assembly and monitor tuning voltage and
RF output.
2. Select channel frequency of 117.95 MHz and adjust turn spacing on synthesizer for
7.0 vdc on tuning line.
3. RF output shall be 9.0 +/- 1 db.
H. Transmitter (Dwg. SS1881)
The transmitter consists of 4 RF power amplifiers. The first amplifier Q4 is gated on by
power received from the frequency synthesizer. Q1, Q2, and Q3 form a broad-band
collector modulated transmitter chain.
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