Strange "2nd" control channel on a P25 trunked system

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Mikek

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Using DSD+ Fastlane, I am seeing what looks like a 'second' control channel on a P25p1 system. This is the data stream from that channel:
77817

This obviously isn't typical control channel traffic, but does line up with what the 'true' CC is doing. Can someone explain what I am seeing? I have never noticed this data stream before, and I have been watching this system for a long time. Thank you!
 

glradio

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It's obviously Orange County, CA. What are the frequencies of the control channel and the second control channel? Also, what are you using to receive the CC data?
 

u2brent

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Data is the key word. If the system uses OTA it could be a large data transmission.

Example:
Channel 4-1379: 153.4475 CC SCC
Channel 8-2756: 153.4475-1 VOICE
Channel 4-1445: 153.6125 CC SCC DATA
Channel 8-2888: 153.6125-1 VOICE
Channel 8-2889: 153.6125-2 VOICE
Channel 4-1763: 154.4075 DATA BSI
Channel 8-3524: 154.4075-1 VOICE
Channel 8-3525: 154.4075-2 VOICE
 

GTR8000

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See this thread:

 

wa8pyr

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Data is the key word. If the system uses OTA it could be a large data transmission.

Example:
Channel 4-1379: 153.4475 CC SCC
Channel 8-2756: 153.4475-1 VOICE
Channel 4-1445: 153.6125 CC SCC DATA
Channel 8-2888: 153.6125-1 VOICE
Channel 8-2889: 153.6125-2 VOICE
Channel 4-1763: 154.4075 DATA BSI
Channel 8-3524: 154.4075-1 VOICE
Channel 8-3525: 154.4075-2 VOICE
If the data transmissions are lengthy it's probably OTAP (Over The Air Programming) or OTAR (Over The Air Rekeying).
 

blantonl

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Interesting - I just came across this exact same scenario on the USAF P25 system in San Antonio.

It looked (and sounded) like another control channel popped up on the site, but was a super long transmission of this exact same of data, as shown in DSD. It would go for 30-90 seconds and then restart...

They must have been rekeying or reprogramming a bunch of radios.
 

Mikek

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It's obviously Orange County, CA. What are the frequencies of the control channel and the second control channel? Also, what are you using to receive the CC data?
857.4625 was the control channel, and this data was on 856.7125 (Countywide cell). I'm using DSD+ and an Airspy R2.

Interesting - I just came across this exact same scenario on the USAF P25 system in San Antonio.

It looked (and sounded) like another control channel popped up on the site, but was a super long transmission of this exact same of data, as shown in DSD. It would go for 30-90 seconds and then restart...

They must have been rekeying or reprogramming a bunch of radios.
That's probably it - as some of the frequencies shown are control channels for other 'cells' in the system...
 

slicerwizard

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Toronto, Ontario
See this thread:

That's not helpful here. The steady TDULC stream posted by the OP is a data channel. Watch the control channel for messages steering subscribers to the data channel. Could be used for OTAR, AVL, ...
 
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