Planning for maintenance of a radio telemetry system does not entail just having the correct amount of spares, but also scheduling preventative maintenance. Radio systems in general require some measure of "test and re-calibration" program to be put in place as the radio systems themselves will, and do drift in frequency over time.
If the system is in an isolated and remote location the likelihood that all the crystals will drift together is fairly high, especially if manufactured about the same time. The result is all modules will be operating on the same frequency and no other system is likely to be interfered with as there is nothing there to disturb.
When systems are installed in radio dense areas such as urban developments, then care must be taken that the system is kept within the limits of frequency error allowed such that "neighbours" are not interfered with.
This type of maintenance is best left to trained personnel such as radio technicians or two-way radio companies. This does not mean that such errors cannot be done by yourself although it is strongly recommended that advice be sought from the suppliers of the equipment before planning or embarking on such maintenance.
The best times for such maintenance is within the first year of service and then every two years after that. Temperature does affect the frequency and before adjusting all the units a global error should be ascertained, it may be found that all units are within ±0.5kHz of each other. This is acceptable as long as globally the error is no more than plus or minus 1.5kHz of the desired operating frequency.
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