P25 Decoding

thunderr10

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Why do you only receive the digital data noise when searching or using tone-out for 700-800Mhz P25 Phase 2 systems? When using the frequency search feature of the scanner, it will stop on a phase 1 frequency and decode the audio, but when it stops on a phase 2 frequency, you only hear the digital sound and it won't decode the voice. These are frequecies from non-encrypted systems that I'm listening to. Phase 2 works fine when I program the system into the scanner for normal scanning.
 
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thunderr10

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I can't seem to edit my last question anymore, so here is a change to it. Where it said phase 1, it should be P25 Motorola Type II SmartZone. "Why do you only receive the digital data noise when searching or using tone-out for 700-800Mhz P25 Phase 2 systems? When using the frequency search feature of the scanner, it will stop on a P25 Motorola Type II SmartZone frequency and decode the audio, but when it stops on a phase 2 frequency, you only hear the digital sound and it won't decode the voice. These are frequecies from non-encrypted systems that I'm listening to. Phase 2 works fine when I program the system into the scanner for normal scanning. "
 

trentbob

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I can't seem to edit my last question anymore, so here is a change to it. Where it said phase 1, it should be P25 Motorola Type II SmartZone. "Why do you only receive the digital data noise when searching or using tone-out for 700-800Mhz P25 Phase 2 systems? When using the frequency search feature of the scanner, it will stop on a P25 Motorola Type II SmartZone frequency and decode the audio, but when it stops on a phase 2 frequency, you only hear the digital sound and it won't decode the voice. These are frequecies from non-encrypted systems that I'm listening to. Phase 2 works fine when I program the system into the scanner for normal scanning. "
Sounds like post 3 is your answer, I too would like to know what radio you're listening to but I also wanted to let you know for future reference...

You have 30 minutes to edit a post, then it's locked.
 

buddrousa

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For the P25 Kevin has the answer Uniden needs control channel data info
 

thunderr10

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Uniden SDS100 is the scanner I'm using. The control channel explanation makes sense, now that I think about it. Thanks for the replies.
 

btt

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The seed for the Phase 2 scrambler needs wacn, sys_id, and nac in order to initialize the matrix. These 3 values are provided by the control channel.
seed = (uint64_t) (16777216*(uint64_t)wacn + 4096*(uint64_t)sys_id + (uint64_t)nac);
 
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