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21
Wireless Solutions for Advancing Communications
Spurious Operations
Occasional spurious (unexpected) operations are nearly inevitable. Usually the spurious operations
are not caused by a defect in this equipment. For airport lighting, some possible causes of these
“spurs” include:
1. An aircraft intending to operate lights at another airport accidentally transmits on the wrong
frequency, or both airports use the same frequency for light control.
2. Two aircraft transmit simultaneously on the channel with transmitters whose frequencies
differ by less than 20 Hz (causing a low frequency heterodyne)
3. An aircraft transmits with a defective transmitter, microphone, cables, or antenna system
(“cuts in and out” or “breaks up”). Certain lightning static patterns from in-range electrical
storms. If pilots feel that the operating range is greater than necessary and that spurious
operations are troublesome and may be caused by distant aircraft, the sensitivity of the
receiver can be reduced. (See the section on Adjustment). It may be necessary to
experiment with several settings before finding the best one for a particular installation.
Microphone clicks must be at least 1/20 second long to register. If the sequence of clicks is
too slow, the 5 second window may expire before the last click is counted. The pilot should
make certain his radio is tuned to the correct frequency and should be aware that the range
of operation is dependent on altitude. In some installations, the range will be less for aircraft
approaching from some directions, due to multi-path reflections of the radio signal or to
shadowing from hills and buildings.
