Simulcast refers to wide area coverage achieved by having multiple transmitter sites that transmit exactly the same audio on exactly the same RF frequencies. Problems relating to RX of out of phase signals (e.g. by RXing signals from two sites that are at different distances) are reduced by engineering the system to provide a stronger signal from one site in any overlap areas (so the FM capture effect takes over).
Simulcast is not necessarily bad for this particular application, but scanner users run in to two problems:
- Many scanners don't handle simulcast signals very well.
- Many scanner listeners monitor from outside the engineered coverage area and have to deal with multiple out of phase signals that arrive with similar RF power levels, so there is no capture effect to filter out the weaker signal(s). The usual solution is a beam aimed so as to null out the most problematic signal.
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