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Page 4-32
GNS 400W Series Maintenance Manual
Rev. A
190-00356-05
Selectivity
Nose Bandwidth 25 kHz channel mode: The input signal level required to produce the reference
AGC voltage must not vary more than 6 dB over the input signal frequency range of ±8 kHz from
the assigned channel frequency. Measure at channel 127.000.
Skirt Bandwidth 25 kHz channel mode: At frequencies displaced by 17 kHz on either side of the
assigned channel frequency, the input signal level required to produce reference AGC voltage
must be at least 40 dB greater than the level required to produce reference AGC voltage at the
assigned channel frequency. At frequencies displaced by 25 kHz on either side of the assigned
channel frequency, the input signal level required to produce reference AGC voltage must be at
least 60 dB greater than the level required to produce reference AGC voltage at the assigned
channel frequency. Measure at channel 127.000.
Nose Bandwidth 8.33 kHz channel mode: The input signal level required to produce the reference
AGC voltage must not vary more than 6 dB over the input signal frequency range of ± 2.778 kHz
from the assigned channel frequency. Measure at channel 127.005.
Skirt Bandwidth 8.33 kHz channel mode: At frequencies displaced by 7.37 kHz on either side off
the assigned channel frequency, the input signal level required to produce reference AGC voltage
must be at least 60 dB greater than the level required to produce reference AGC voltage at the
assigned channel frequency. Measure at channel 127.005.
Nose Bandwidth
1.
Enable the audio compressor.
2.
Select 25 kHz or 8.33 kHz channel spacing mode.
3.
Set the volume to minimum.
4.
Generate an RF signal with no modulation, an RF carrier frequency of 127.000 mHz,
and an RF signal level of –93 dBm (10 µV).
5.
Measure the IF AGC voltage. This is the reference AGC voltage.
6.
Set the RF signal level to –87 dBm (20 µV).
7.
Set the RF frequency to 127 + offset frequency (8 kHz or 2.778 kHz for 25 or 8.33
spacing respectively).
8.
Measure the AGC voltage. This is the fc (+) voltage.
9.
Set the RF frequency to 127 – offset frequency (8 kHz or 2.778 kHz for 25 or 8.33
spacing respectively).
10.
Measure the AGC voltage. This is the fc (-) voltage.
11.
Verify (reference AGC voltage) – (offset AGC voltage)
≤
0.