Voice Channel

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milcom_chaser

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So if I park a Uniden Phase II capable scanner on the voice channel of a P-25 phase II system. Why won't the radio decode the voice channel? What is it about Phase II decoding that works as a programmed system (control and voice channels) vs listening to just the voice channel?

Is the data containing the voice passed to the control channel, and the radio decodes it from there?
 

jonwienke

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There are generally multiple voice channels on a site. The control channel tells the scanner which one will be used for a given transmission. If you're monitoring a voice channel only, it may happen to be one that is only rarely used.
 

milcom_chaser

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There are generally multiple voice channels on a site. The control channel tells the scanner which one will be used for a given transmission. If you're monitoring a voice channel only, it may happen to be one that is only rarely used.
No. This is a busy multi-site system. The voice channels are indeed active...
 

jonwienke

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That doesn't mean every one will be active. A site can be programmed such that a particular voice channel is only used when all other voice channels are busy--voice channel D is only used if channels A, B, and C are already in use.

If you're monitoring D, you may never hear anything unless there is a major incident with lots of conversations going on that simultaneously tie up channels A, B, and C.

I get P25 Close Call hits on a regular basis that are voice channels from trunked systems. You get random bits of conversations without the control channel data, but you hear stuff.

Also, are you sure you're listening to a voice channel? If you listen to the control channel conventionally, the scanner will detect P25 data, but won't ever break squelch because the frequency isn't carrying any actual voice data.
 

milcom_chaser

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That doesn't mean every one will be active. A site can be programmed such that a particular voice channel is only used when all other voice channels are busy--voice channel D is only used if channels A, B, and C are already in use.

If you're monitoring D, you may never hear anything unless there is a major incident with lots of conversations going on that simultaneously tie up channels A, B, and C.

I get P25 Close Call hits on a regular basis that are voice channels from trunked systems. You get random bits of conversations without the control channel data, but you hear stuff.

Also, are you sure you're listening to a voice channel? If you listen to the control channel conventionally, the scanner will detect P25 data, but won't ever break squelch because the frequency isn't carrying any actual voice data.
Yes, I'm listening to a voice channel as I confirmed it with Unitrunker and a second radio in analog mode.
What's interesting is with the Uniden 325P2, the radio decodes fine with a programmed system containing control channels and voice. Yet, when you do a Control Channel only search in the 800 mhz band, and come across a control channel, the radio begins to trunk, tracks the voice channels correctly, but the digital content is not decoded. You can hear the digital, but it's not decoded. So this maybe a firmware issue for Control Channel only searching when encountering a P-25 Phase II system. If there were other users of the bcd325P2 or 996P2 we could confirm this phenomena...
by having them search for a control channel only in the 800 band, and observe the results.
 

jonwienke

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It's something specific to your scanner model then, not Uniden scanners in general. The x36 scanners decode P25 audio, even if the channel is programmed as conventional.
 

KevinC

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It's something specific to your scanner model then, not Uniden scanners in general. The x36 scanners decode P25 audio, even if the channel is programmed as conventional.
I'm pretty sure they won't decode P25 TDMA that way. They probably need info from the CC (slot number, TG and so on)...but I could be wrong.
 

milcom_chaser

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I'm pretty sure they won't decode P25 TDMA that way. They probably need info from the CC (slot number, TG and so on)...but I could be wrong.
Yes, someone else confirmed that. Good to know.
Thanks for chiming in.
 

milcom_chaser

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It's something specific to your scanner model then, not Uniden scanners in general. The x36 scanners decode P25 audio, even if the channel is programmed as conventional.
Well, yes and no. Trying tuning your Uniden to a voice channel for a P-25 Phase II system. That is, if you
have a Phase II compatible radio.
 
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troymail

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It's something specific to your scanner model then, not Uniden scanners in general. The x36 scanners decode P25 audio, even if the channel is programmed as conventional.
I do not believe Uniden will process a P25 Phase 2 signal if programmed as conventional -- so I believe your are saying the radio does something that it does not.
 

milcom_chaser

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I do not believe Uniden will process a P25 Phase 2 signal if programmed as conventional -- so I believe your are saying the radio does something that it does not.
Indeed. After a refresh on TDMA theory: "TDMA systems typically require timing from the radio base station equipment via the system control channel and traffic channels for slot synchronization. This makes direct-mode operations challenging for TDMA when no master timing reference from a base station is present."
 
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