discuss-gnuradio
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Discuss-gnuradio] Trunking


From: Dave Emery
Subject: Re: [Discuss-gnuradio] Trunking
Date: Mon, 4 Nov 2002 22:07:38 -0500
User-agent: Mutt/1.4i

On Mon, Nov 04, 2002 at 03:46:51PM -0800, Jordan Hayes wrote:
> Has anyone thought about what might be required to decode trunking
> information and perhaps record all trunks for later
> playback/synchronization?
> 

        I have thought of trying it, but haven't got around to doing so
yet...

        The primary thing required is a fast enough A/D and computer to
process the entire band from the lowest trunking channel in use to the
highest.   On 800 mhz this can be up to about 15 or 16 mhz with current
allocations (may change soon with the Nextel NPRM).

        This implies around 35 to 50 megasamples per second, which is
certainly doable but somewhat beyond the capabilities of the  current
A/D converter used with existing prototypes.

        One has a certain advantage in that all the channels in use on
one site are apt to be similar in level, thus one may not need as great
a dynamic range as for some other radio traffic.   (But of course if
there are strong Nextel or other local 800 band signals one may need the
dynamic range anyway just to not be blocked by them).

        Actually processing the data stream and extracting the narrow
band fm or digital channels should be quite possible with the current
code.   Obviously dealing with the trunking control channel protocols is
something for which a good bit of public domain code exists now, so
actually sorting out the activity on the trunk should be pretty easy
once one has got up to 28 individual FM or FSK demodulators running at
once in real time.

        And recording all the channels into audio files with appropriate
timing information should be pretty easy and I think some of the MPEG
video timing sychronizing stuff could be used to cross correllate timing
on the various streams.   Or one could decode the control channel and
sort the audio files on the fly into MP3s for each talk group stored on
a hard drive in a big directory.


-- 
        Dave Emery N1PRE,  address@hidden  DIE Consulting, Weston, Mass. 
PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2  5D 27 BD B0 24 88 C3 18





reply via email to

[Prev in Thread] Current Thread [Next in Thread]