SGC SG-2020 TEST DOCUMENT Test Manual page 5

3.0 LPA BIAS
This is not a routine procedure and should be done only when the final
transistors are replaced.
3.1 Set display for 14150.0 KHz, USB.
3.2 Connect voltmeter across bias test points TP1 and TP2 on LPA (across
R29, LPA page 3/3), key the SG-2020 (with no RF input), and verify
that the meter reads 7 mV. Readjust R7 on LPA if necessary.
4.0 ADJUST REVERSE DETECT VOLTAGE
4.1 Set the display for 14150.0 KHz USB.
4.2 Connect audio generator to microphone input. Set for 1300 Hz @ 15
mV output.
4.3 Connect voltmeter set on millivolt scale to TP5 (REV) and GND on the
LPA.
4.4 Set power to P20 by pressing "CMD" + "NB" then adjust spinner
to 20. Press "MEM".
4.5 Key PTT and verify 20 watts output power. Readjust the audio genera-
tor below the ALC level kick-in (or until 20 watts reads on wattmeter).
4.6 Adjust C56 on LPA for min. voltage on TP5 (less than 50 millivolts)
5.0 RADIO CALIBRATION
5.1 Set the radio to 3,700.0 KHz, USB.
5.2 Turn off power.
5.3 Turn power back on and immediately press and hold CMD until "C"
appears on display.
5.4 Release "CMD" button and then immediately (before function time-out
occurs) press "BW" button - "CA" should be shown on display.
5.5 Immediately press 'LIGHT' button - "CAL" should be displayed. You
are now in calibration mode and the number 1 (one) should appear on
left side of display along with a reference reading on the right side.
Identify calibration data for the exciter in the radio
5.6 You will need the data results from the test N920ExcFilterSweep
(Exciter filter sweep).
Calibration
5.7 The radio should be warmed up for at least 20 minutes to
allow everything to stabilize. Connect oscilloscope probe to the indi-
cated REF. point in paragraph 5.9 and adjust tuning knob until desired
frequency is displayed on the frequency counter (connected with the
scope). Observe and record reading on LCD display and press 'MEM'
to store this reading.
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