Garmin GNS 400W Series Maintenance Manual page 51

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Audio Output Variation
1. Set the unit to 25 kHz mode, the channel to 127 mHz.
2. Find the rated audio input level.
3. Take a reference reading with a 5 µV input.
4. Set the test set to a 100,000 µV input.
5. Compare the reading at 100,000 µV to the reading at 5 µV. Verify no more than 6 dB
difference in readings.
Signal Pin Signal Name
J2-7 COMM AUDIO HI
Receiver Sensitivity
The S+N/N ratio on all channels should be greater than 6 dB when a 30% modulated, 1 kHz
audio frequency, 2 µV RF signal is applied. Measure the sensitivity in the 25 kHz channel mode
at 118.025, 127.000, and 136.975 kHz, and in the 8.33 kHz channel mode at 118.030, 127.005,
and 136.980 kHz.
1. Set the channel spacing to either 25 or 8.33 kHz mode and select the receive test channel.
2. Adjust the test set for the selected channel frequency, 30% modulation, 1 kHz audio
frequency, 2 µV RF output.
3. Measure the SNR. Verify no less than 6 dB SNR on all tested channels.
Signal Pin Signal Name
J2-7 COMM AUDIO HI
TX Interlock
The receiver sensitivity must be reduced by at least 15 dB when the TX interlock line is enabled.
1. Set the channel spacing to 25 kHz mode.
2. Disable the TX INTERLOCK pin (high or open).
3. Generate an RF signal at 127.000 mHz, with 30% modulation at 1 kHz, RF output of –73
dBm.
4. Set the volume for rated audio output.
5. Set the RF level to –107 dBm (2 µV).
6. Measure the SNR (average 10 readings).
7. Enable the TX INTERLOCK pin (low or grounded). Set the RF level to –92 dBm (11.25
µV).
GNS 400W Series Maintenance Manual
190-00356-05
Reference Pin Reference Name
J2-19 COMM AUDIO LO
Reference Pin Reference Name
J2-19 COMM AUDIO LO
Load
500 Ohms
Load
500 Ohms
Page 4-25
Rev. A