P25 digital scanning, control channel only- BC796D

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picree

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In order to trunk a new P25 digital system I followed the advice given here and only programmed in the control channel. I have no other frequencies programmed in my scanner (even though they are listed in the RRDB). It seems to work fine. However, I have a question about bandwidth.

I thought the whole concept behind trunking was for the system to be able to juggle a large number of transmissions across several frequencies in order to maximize the use of multi-frequency bandwidth. Well, how is it that I can pick up "all" transmissions (point made here in the forum) with only the control channel programmed? What are the other frequencies for? Am I missing transmissions on the other frequencies? Surely with hundreds of talkgroups this method will miss some transmissions right?

Confused...
 

garys

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The control channel is just that. All radios on the system always listen to the control channel. That constant stream of data you hear is directing the radios to perform certain functions. When a user keys his microphone, the radio sends a signal to the controller. Included in the signal is the ID of the radio, what talk group it is currently affiliated with, and other information. The control channel sends back a signal that directs the radio to select a certain frequency, alerts other radios on the talk group that a user is keying his radio, and so on. So, while all you program in is the control channel, the scanner is able to follow the data stream and select the correct frequency and talk group. All of that goes on behind the scenes without you knowing or caring about it. All you get is the radio traffic you want to hear.

It's more complex than that, but that's the basics of why you only have to program in one or a few frequencies in Control Channel Only mode.
 

picree

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Johnson City, TN
So, I guess then from what you're saying, my scanner is actually trunking behind the scenes to other frequencies even though I don't have any programed in? So I really am catching all the conversation?
 

torontokris

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yes the scanner goes/jumps to the voice frequencies (even if you dont have them programmed in).

youd be catching all of the conversation, not missing anything by doing the Control Channel only method
 
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