Tcxo Frequency Adjust; Vco Test; Transmit Modulation Adjust - Viking VX 900 MHz LTR User Manual

ALIGNMENT AND TEST PROCEDURES
5. Press the space bar to unkey the Exciter.

7.3.4 TCXO FREQUENCY ADJUST

1. Tune TCXO Y401 for 3.5V DC ±0.05V DC at
U402, pin 1 (response time is very slow).

7.3.5 VCO TEST

1. The Synthesizer is programmed for 199 channels
above the transmit frequency.
2. Press the space bar to key the Exciter.
3. Measure the voltage on U403, pin 6 (TP1). Voltage
should be < 7V DC and the Power Output +17.5
dBm ±0.5 dB.
4. Press the space bar to unkey the Exciter.
5. The Synthesizer is programmed for 199 channels
below the transmit frequency.
6. Press the space bar to key the Exciter.
7. Measure the voltage on U403, pin 6 (TP1). Voltage
should be > 2.5V DC and the Power Output +17.5
dBm ±0.5 dB.
8. Press the space bar to unkey the Exciter.

7.3.6 TRANSMIT MODULATION ADJUST

1. Connect a 10 dB pad and modulation analyzer to
J402.
2. Press the "FM" and "3 kHz LPF" switches of the
modulation analyzer.
3. Inject a 1 kHz sine wave with a level of 400 mV
RMS into P100, pin 32 on the MAC.
NOTE: This test changes the Audio Deviation Limit.
Perform test in Section 7.6.6 to correct.
4. Adjust U149 for 707 mV RMS on P100, pin 29.
This waveform should be a "clean" sine wave.
5. Press the space bar to key the Exciter.
6. Set R446 for ±1.5 kHz deviation.
October 1999
Part No. 001-2009-201
7. Press the space bar to unkey the Exciter.
NOTE: Ensure that the oscilloscope is "DC" cou-
pled and the Modulation Analyzer has the
3 kHz LPF switch set but NOT the 300 Hz HPF and
50 Hz HPF switches set.
8. Adjust U151 for a 2V P-P square wave on P100, pin
29.
NOTE: This test changes the TX Data Level. Per-
form test in Section 7.6.6 to correct.
9. Press the space bar to key the Exciter.
10.Set R425 for "best" square wave as observed on the
oscilloscope.
11. Press the space bar to unkey the Exciter.
12.Repeat Steps 1-7. Very little adjustment of R446
should be needed.
J402
L404
Figure 7-2 EXCITER ALIGNMENT POINTS
7-4
J401
20
2
19
1
R425
J403
Y401
20
1
6
11
10
8
5
U404
1 4
R446