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Re: [Discuss-gnuradio] Motorola IIi Hybrid Trunk decoding

From: ikjtel
Subject: Re: [Discuss-gnuradio] Motorola IIi Hybrid Trunk decoding
Date: Sat, 9 Apr 2011 07:50:53 -0700 (PDT)

> Has anyone written a motorola trunk decoder for gnuradio? I'd like to be
> able to dump all active audio in a trunk to separate streams by
> talkgroup. I'd love to know about any trunk decoders in general.

In addition to Nick's Moto Smartnet II decoder on CGRAN, the op25-dev project 
also has a trunked system receiver for P25 systems.

At this moment the trunk control channel isn't actively parsed in real time.  
Instead all of the channels of the trunked system, including the control 
channel, are logged to disk (or routed to asterisk app_rpt).  

Generally, all the voice channels are decoded to audio and relayed to the VOIP 
world (asterisk app_rpt), whereas the control channel data would be routed over 
a UDP "connection" for logging in Wireshark.  We also have a Wireshark parser 
for P25 frames although it currently doesn't delve very deeply into the P25 
trunk control protocol message (TSBK) frames.

Finally would like to mention that our receiver works well with so-called 
"CQPSK/LSM" systems from Motorola - the "simulcast" distortion has caused a lot 
of trouble for attempts to receive this type of modulation using other 
reception methods such as FM-based systems (i.e., any radio using demodulated 
FM - a.k.a. the disc. tap) - this includes several commercial receivers 
marketed today...



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