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Page 4-28
GNS 400W Series Maintenance Manual
Rev. A
190-00356-05
Noise Level
The S+N/N ratio of the comm radio receiver audio must be at least 35 dB when an input signal is
modulated 30% at 1000 Hz and the RF level is at 100 µV.
1.
Set the unit for 127 mHz in the 25 or 8.33 kHz mode.
2.
Set the signal generator for 127 mHz carrier, 1 kHz audio, 30% modulation, 100 µV
output level.
3.
Read the SNR.
4.
Verify SNR
≥
35dB.
Signal Pin
Signal Name
Reference Pin
Reference Name
Load
J2-7
COMM AUDIO HI
J2-19
COMM AUDIO LO
500 Ohms
Audio Compressor
The audio level should not vary more than 3 dB as the modulation is varied between 30% and
85% at 1000 Hz when the RF is at 100 µV and the compressor is enabled.
1.
Enable the compressor.
2.
Set the unit for 25 kHz channel spacing with the compressor enabled.
3.
Set the signal generator for a 127 mHz carrier frequency, 1 kHz audio frequency,
30% modulation, 100 µV output level.
4.
Measure the ac level in dBm.
5.
Set the signal generator for 85% modulation.
6.
Measure the ac level in dBm and verify difference in levels
≤
3 dBm.
Signal Pin
Signal Name
Reference Pin
Reference Name
Load
J2-7
COMM AUDIO HI
J2-19
COMM AUDIO LO
500 Ohms
Squelch
The carrier squelch must operate in 25 kHz and 8.33 kHz modes. In 25 kHz mode the carrier
squelch must open the audio output when the RF level is between 6.3 and 25.0 µV, modulated
85% at 8 kHz. In 8.33 kHz mode the carrier squelch must open the audio output when the RF
level is between 1.5 and 6.0 µV, modulated 85% at 8 kHz. The carrier squelch must close the
audio output within 6 dB of opening squelch level. Carrier squelch operation must be tested at the
channels shown below in 25 kHz and 8.33 kHz channel modes.
