As it has come up a few times in recent posts, I figured I'd mention something on Simulcast systems, especially analog ones like Concord Fire Alarm, Lakes Region, New London, and Southwestern Mutual Aid.
The systems utilize multiple sites that vary in number and the dispatcher will rarely know at the moment which sites are active. They push one transmit button. From a scanning perspective, there are some clues on analog, like a degraded signal in certain areas, or hetrodyning (mixing) signals indicating a hand-off area. But rarely would even a scanner or radio listener really know what sites are up or down. A degraded signal may also be because of distance from the nearest site, condition of the receiving equipment, geography of the area the receiver is in, atmospheric conditions like solar flares, the season (Summer vs Winter), heavy snow, rain, wind, etc.
Simulcast is in theory counterintuitive in that when multiple transmitters key up at once on a single frequency, they should be interfering with each other. Simulcast uses very precise location, signal strength, timing delays of the transmission and probably other stuff I forgot to avoid interfering with each other.
So if you're not sure if an area has a site down, some extra current and historical research is necessary, especially if it happens often.
John
The systems utilize multiple sites that vary in number and the dispatcher will rarely know at the moment which sites are active. They push one transmit button. From a scanning perspective, there are some clues on analog, like a degraded signal in certain areas, or hetrodyning (mixing) signals indicating a hand-off area. But rarely would even a scanner or radio listener really know what sites are up or down. A degraded signal may also be because of distance from the nearest site, condition of the receiving equipment, geography of the area the receiver is in, atmospheric conditions like solar flares, the season (Summer vs Winter), heavy snow, rain, wind, etc.
Simulcast is in theory counterintuitive in that when multiple transmitters key up at once on a single frequency, they should be interfering with each other. Simulcast uses very precise location, signal strength, timing delays of the transmission and probably other stuff I forgot to avoid interfering with each other.
So if you're not sure if an area has a site down, some extra current and historical research is necessary, especially if it happens often.
John
