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Page 4-36
GNS 400W Series Maintenance Manual
Rev. A
190-00356-05
Channel Selection Time
NOTE
Use an oscilloscope to perform this test.
The time required for the receiver audio to reach and remain within 3 dB of steady-state output
must not exceed 100 msec when any channel is selected.
1.
Enable the audio compressor.
2.
Select 25 kHz channel spacing.
3.
Generate an RF signal with 30% modulation, a modulation frequency of 1,000 Hz, an
RF carrier frequency of 136.975 mHz, and an RF input level of –53 dBm.
4.
Set volume for rated output.
5.
Select 118.000 mHz as the standby frequency.
6.
Ground the COMM REMOTE TRANSFER pin (J2-15). This will switch the active
frequency to 118.000 mHz.
7.
Ground the COMM REMOTE TRANSFER pin (J2-15). This will return the receiver
to 136.975 mHz. Observe and capture the waveform showing the time it takes for the
audio output to stabilize. Scope must be triggered with the remote transfer signal.
8.
Ground the COMM REMOTE TRANSFER pin (J2-15). This will return the receiver
to 118.000 mHz. Observe and capture the waveform showing the time it takes for the
audio output to stabilize. Scope must be triggered with the remote transfer signal.
Verify the audio output stabilizes in < 100 msec.
Signal Pin
Signal Name
Reference Pin
Reference Name
Load
J2-7
COMM AUDIO HI
J2-19
COMM AUDIO LO
500 Ohms
Birdie Channels
The equivalent carrier level must not be greater than 0.5 µV on all channels. AGC reference is
taken from an adjacent channel. Known birdie channels in the 25 kHz mode are: 119.750,
130.950, 131.725, 128.000, and 118.000. Known birdie channels in the 8.33 kHz mode are
119.735, 119.740, 119.760, 119.765, 131.710, 131.715, 131.735, 131.740 and130.940.
1.
Set the unit channel spacing to 25 kHz.
2.
Set the unit channel to a known birdie channel.
3.
Generate a signal at a known birdie channel with 30% modulation, 1kHz modulation
frequency, and an output level of 2 µV.
4.
Measure the SNR (averaged over 10 readings). Store the result.
5.
Repeat steps 1-4 for each birdie channel. Verify the measured SNR
≥
6.0 dB.