P25 trunking site NAC codes

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Anderegg

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I am going to program trunked input frequencies into my scanner to hear close by radios, and I am wondering if the radios transmit using the site NAC code, or if they are just CAI P25 into the repeaters.

Paul
 

GTR8000

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A P25 transmission is always accompanied by a NAC. While the subscribers will likely use the Site NAC for inbound transmissions, you're probably better off setting the scanner to NAC search, at least in the early going to verify the correct NAC.
 

Anderegg

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Thanks guys. My citys old 3600 system had a connect tone of 136.45Hz, which allowed me to sucessfully use CTCSS of 136.5Hz to eliminate unwanted transmissions...heh. I wasn't sure how digital trunking worked though.

Paul
 
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GTR8000

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Bit of trivia...3600 systems that have P25 CAI talkgroups also use a NAC on those digital transmissions. Obviously you're not going to be using a Connect Tone with digital modulation.

You can probably forgo the NAC when monitoring inputs, as it's pretty unlikely that anyone else is going to be transmitting on those frequencies in the area.

PS - You'll only be able to monitor P25 FDMA transmissions on the input frequencies. No scanner is capable of decoding P25 TDMA on inputs; only on the outputs and only when trunk tracking the system (i.e. no TDMA decoding in conventional mode at all)
 
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