Reference Oscillator Alignment - Motorola ASTRO SPECTRA Service Manual

Radio Alignment Procedure: RSS
6.2.3

Reference Oscillator Alignment

Radios are shipped from the factory with a worst-case frequency error of ±200 Hz for VHF, ±300 Hz
for UHF, and ±500 Hz for 800 MHz. These specifications are tighter than the more stringent FCC
requirement of 1.5 ppm for all bands.
For radios that have been in storage for over six months from the factory ship date, the reference
oscillator should be checked when the radio is initially deployed to the field. It is strongly
recommended that the reference oscillator be checked every time the radio is serviced or at least
once a year, whichever comes first.
The crystal contained in the reference oscillator naturally drifts over time due to its aging
characteristic. Periodic (annual) adjustment of the reference oscillator is important for proper radio
operation.
Improper adjustment can result in both poor performance and interference with other users operating
on adjacent channels.
This test can be done with either the R-2670 Communication Analyzer or the 8901_ Modulation
Analyzer.
1. Initial set up using the R-2670 Communication Analyzer:
- RF Control: MONITOR
- B/W: WB
- Freq: RSS frequency under test
- Attenuation: 20dB
- Mon RF in: RF I/O
- Meter: RF Display
- Mode: STD
- Input Level: uV or W
- Display: Bar Graphs
- Squelch: Mid-range or adjust as necessary
2. Initial set up using the 8901_ Series Modulation Analyzer:
- Press the green Automatic Operation button on the analyzer.
- Press the FREQ key.
- Type 7.1 followed by the SPCL button to set the 8901_ modulation analyzer for maximum
accuracy.
3. Read the radio using the RSS.
4. From the SERVICE MENU, press F2 to select the TRANSMITTER ALIGNMENT MENU.
5. Press F2 again to select the REFERENCE OSCILLATOR alignment screen (
6881076C20-E
6-3
Figure 6-4 ).
February 3, 2003