simulcast reception

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lu81fitter

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I am aware that every system in a P25 radio "group" has a system ID. In simulcast, does each tower or site within the system have its own specific ID? Does the subscriber radio tune to the tower/site that is giving it the best reception/signal electronically to eliminate distortion? And maybe a scanner cannot "affiliate" in this manner? Maybe this has been discussed or I may be off base with this idea. I am just trying to learn more about programming digital systems as I will be purchasing a digital scanner soon.
 

Thunderknight

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Simulcast works by timing all of the tower transmissions so the radios receive them all at about the same time. (Close enough such that the data bits don't cancel each other out). The timing is within milliseconds.

There is NO difference in the actual transmission between the sites in a simulcast cell. All sites in the same cell transmit the same RFSS and Site ID.

The issue with scanners has to do with their inability to handle the multiple signals arrive close together. An actual P25 radio has a different receiver design that is capable of handling these small time of arrival differences. (if they get too large, then even a real radio won't be able to handle it and the signal will get distorted or lost).
 

GTR8000

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  • Simulcast = Simultaneous Broadcast
  • RF Subsite = A physical transmitter location
  • Simulcast Cell = A group of RF subsites that comprise a single site

Every RF subsite in a simulcast cell transmits the exactly identical signal on the exactly identical frequencies.

It doesn't matter if there are two or twenty RF subsites in the simulcast cell; it all appears as one signal to any type of receiver, and there is nothing that distinguishes between them.

This is true regardless of whether the receiver is a top of the line Motorola APX radio, or a consumer grade scanner.
 
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