Reference Oscillator; Preventative Maintenance; Reference Oscillator Alignment - Motorola ASTRO XTS 3000 Service Manual

Reference Oscillator

7.2 Reference Oscillator
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The following section describes service of the reference oscillator.

7.2.1 Preventative Maintenance

Radios are shipped from the factory with worst-case frequency error of +/- 250 Hz for VHF, +/-750 Hz for
UHF, +/-750Hz for 800 MHz and +/- 1KHz for 900 MHz. These specifications are tighter than the most
stringent FCC required specs of 2 ppm, 2 ppm, 1.5 ppm and 1.5 ppm (part per million) for VHF, UHF,
800 MHz, and 900 MHz respectively, within which the radio will operate to specification.
For radios that have been in storage for over 6 months from the factory ship date, the reference oscillator
should be checked upon initial radio deployment to the field. It is also strongly suggested that the reference
oscillator be checked every time the radio is serviced or once a year, whichever comes first.
The crystal contained in the reference oscillator naturally drifts over time due to its aging characteristic. This
drift can be expected to be in the negative direction from the original factory setting. Therefore, periodic
(annual) adjustment of the reference oscillator is important for proper radio operation. Improper adjustment
can result not only in poor performance, but also in interference with other users operating on adjacent
channels. A recommended test setup and tuning procedure is detailed in the alignment section of this manual.
The frequency counter used for this procedure must have a stability of 0.1 ppm or better.

7.2.2 Reference Oscillator Alignment

Adjustment of the reference oscillator is critical for proper radio operation. Improper adjustment will result
not only in poor operation, but also in a misaligned radio that will interfere with other users operating on
adjacent channels. For this reason, the reference oscillator should be checked every time the radio is serviced.
The frequency counter used for this procedure must have a stability of 0.1 ppm (or better).
This test can be done with either the R2670 Communication Analyzer or the 8901B Modulation Analyzer.
7-4
Some of the following screens may vary depending upon the radio under test and the version of
radio service software you are using. Refer to your Radio Service Software user guide.
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Chapter 7: ALIGNMENT PROCEDURE
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68P81083C85-A March 2004