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DWG ID: 181-0101-01
Date: 2003-08-12
Press the “1” key for the RX FREQUENCY TRIM and set the 1
st
LO on frequency using
a frequency counter connected to the ANT port. (The 1
st
LO frequency is indicated on the
VDT screen next to the RX FREQUENCY). The offset voltage at A2P1-7 will be 2.50
V dc. This setting, if incorrect, will degrade receive sensitivity and distortion.
When in RX FREQUENCY TRIM, certain stages in the transmit chain are enabled,
which cause local oscillator leakage at the ANT connector to be stronger than normal.
Even so, the level may be less than 0 dBm. The frequency counter must be connected
directly to the ANT connector and be able to operate at this level.
CAUTION:
DO NOT PLACE THE UNIT IN A TRANSMIT MODE DURING THIS
PROCEDURE: SERIOUS DAMAGE TO THE COUNTER WILL RESULT.
5.2.3
CARRIER DETECT
•
Set service monitor generator frequency to receive frequency of radio modem
•
No modulation
•
Set service monitor power output to signal level required for carrier-detect to go true.
Press the “2” key for CARRIER DETECT ON TRIM adjustment. Adjust until there is a
constant ON (on the VDT) indicated. This may be monitored at A2AR2-1 with a dc-
coupled oscilloscope. There should be a 5 V dc level with no negative going glitches.
•
Set the service monitor power output to signal level required for carrier-detect to go
false.
Press the “3” key for CARRIER DETECT OFF TRIM adjustment. Adjust until there is a
constant off. The ON indicator (on the VDT) being off indicates this. Continue
monitoring at A2AR2-1 with dc-coupled oscilloscope. There should be a 0-V dc level
with no positive going glitches.
5.2.4
RECEIVER DC OFFSET ADJUST
Set service monitor power output for a level above the carrier-detect on level with 1200
Hz tone at 2.3 kHz deviation modulation on.
Measure V
BIAS
at MX919B IC terminal 21 (A2U3-21).
Press the “4” key for the RECEIVER DC OFFSET ADJUST.
Adjust this to get measured V
BIAS
value at MX919B IC terminal 23 (A2U3-23).
5.2.5
RECEIVER GAIN ADJUST
Set modulation at a 1200 Hz tone for 2.3 kHz deviation.