NGT—Checks and adjustments
NGT Transceiver System Technical Service Manual 191
Checking the AGC
To check the AGC:
1 Set up the equipment as described on page 190, Checking the sensitivity and
(signal+noise)/noise ratio, but set the output of the signal generator to –13 dBm
(50 mV PD).
1 Press 5 to select RF Gain On.
1 Adjust the volume control for a suitable, near full-scale dB reading on the AC
voltmeter.
1 Record the reading.
1 Reduce the output of the signal generator until the receiver output drops by 6 dB.
The signal generator level should be less than –99 dBm (2.5 µVPD).
If the signal generator level is greater than –99 dBm (2.5 µV PD), further analysis is
required.
Checking the audio output
To check the audio output:
1 Set up the equipment as described on page 190, Checking the sensitivity and
(signal+noise)/noise ratio, with a signal generator output level of –67 dBm
(100 mV PD).
1 Connect an oscilloscope in parallel to the AC voltmeter across the audio output
(loudspeaker).
For this test, it is advisable to replace the loudspeaker with an 8 Ω, 5 W resistor.
1 Increase the audio level by adjusting the volume control and check that the audio
output exceeds 12 V p–p at the onset of clipping (displayed on the oscilloscope).
If the audio output does not exceed 12 V p–p at the onset of clipping, further
analysis is required.
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