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GNS 400W Series Maintenance Manual
Page 4-37
190-00356-05
Rev. A
Signal Pin
Signal Name
Reference Pin
Reference Name
Load
J2-2 COMM
IF
AGC
TEST
J2-21 GROUND
None
LO Radiation
The received LO radiation must not exceed - 57 dBm out of the antenna port.
1.
Possible Faulty Circuits: Shielding or Antenna BNC Connector Ground. Check CPU,
Synthesizer, RF Shields for good solder connection to PCB. Check shield covers for
tight fit.
2.
Check BNC antenna connector nut and make sure it is tight against the RF fence.
3.
Set the channel spacing to 25 kHz.
4.
Set the RF carrier frequency to 127.000 mHz.
5.
Ensure that the comm transceiver is not in the transmit mode.
6.
Set the spectrum analyzer for a center frequency of 148.400 mHz, 10kHz/div. span.
7.
Measure the peak RF output power from the comm antenna port.
8.
Verify peak RF output power
≤
-57dBm.
9.
Adjacent Channel Rejection (8.33 kHz mode only)
The adjacent channel rejection (which is the ratio between the desired signal level and the lowest
interfering signal level) must be at least 45 dB under the following conditions: the desired on-
channel signal is modulated 60% at 1000 Hz at a level sufficient to produce a S+N/N of 20 dB
and an interfering signal on the adjacent upper and lower 8.33 kHz channel is modulated 60% at
400 Hz adjusted to a level that reduces the S+N/N of the desired signal from 20 dB to 14 dB.
Signal Pin
Signal Name
Reference Pin
Reference Name
Load
J2-7
COMM AUDIO HI
J2-19
COMM AUDIO LO
500 Ohms
Test manually per instructions found in DO186a 2.2.16.
