P25 Decoding

[thunderr10]

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.

 

[thunderr10]

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. "

 

[KevinC]

You need information from the control channel to decode a Phase 2 call.

 

[buddrousa]

What scanner are talking about?

 

[trentbob]

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]

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

 

[thunderr10]

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]

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);