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GNS 400W Series Maintenance Manual
Page 4-33
190-00356-05
Rev. A
Skirt 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 signal generator for an output of –33 dBm (10,000 µV).
7.
Set the RF signal to (+) offset RF frequency (25 kHz in 25kHz mode, 7.37 kHz in
8.33 kHz mode).
8.
Measure the IF AGC voltage. This is the fc (+) AGC voltage.
9.
Set the RF signal to (-) offset RF frequency (25 kHz in 25 kHz mode, 7.37 kHz in
8.33 kHz mode).
10.
Measure the IF AGC voltage. This is the fc (-) AGC voltage.
11.
Verify (Reference AGC) – (Offset AGC) > 0.
Signal Pin
Signal Name
Reference Pin
Reference Name
Load
J2-2
COMM IF AGC
TEST
J2-21 GROUND
None
Spurious Response
The spurious response rejection is a measure of the capability of the receiver to discriminate
between the wanted modulated signal at the nominal frequency and an unwanted signal at any
other frequency at which a response is obtained.
The input signal level on an undesired frequency required to produce a detector-carrier (AGC)
level equal to that required for a 6 dB noise to noise ratio for 30% modulated, 1000 Hz
modulation on the desired channel at rated audio must be not less that 10 mV when:
The undesired input signal frequency is within 108 to 137 mHz and is on any frequency within ±
8 kHz of any assignable channel other than the selected channel and the upper and lower adjacent
channels.
The undesired input signal frequency between 50 kHz and 1215 mHz excluding the band 108 to
137 mHz.
Spurious response tests must be conducted at image frequencies (channel fre 42.8 mHz)
and at half IF frequencies (channel fre 10.7 mHz). Measurements are performed at
channel 127.000 with image and half IF frequencies shown in the following table: