[op25-dev] Project question

Alex alex323@gmail.com [op25-dev] op25-dev at yahoogroups.com
Thu Sep 22 01:52:19 UTC 2016

On Thu, 22 Sep 2016 11:30:52 +1000
"Matt Ames matt.ames7bc at gmail.com [op25-dev]"
<op25-dev at yahoogroups.com> wrote:

> Hi Alex,
> Some of those ideas/tasks date back to 2008 when the project was its'
> initial embryonic stages. The idea back then was to find a way to
> track a P25 station geographically - for example, using multiple time
> and frequency sync'd USRP's (with GPSDO for location and time sync)
> to do time difference of arrival type location determination, or even
> a Roanoke Doppler style of receiver.
> Since then, Motorola TRBO and DMR has become very popular, and with
> it, services such as LRRP are transmitting data over some of these
> networks. I know that some of the Motorola APX and TRBO series radios
> can be set up to transmit their GPS locations in the clear, which
> could be easily read over the air. This has been done in other
> projects with TRBO, but not with P25 to my knowledge.
> These are just a few ideas I threw around, Balint (with some
> assistance from me) implemented a great SDR Doppler RDF. It wasn't
> tuned for P25 but it did work well on whatever it was tuned to..
> Balint since went to California and worked on another setup using a
> USRP and an algorithm called MUSIC that worked very well...
> In short, there are many ways of determining the direction an RF
> signal is coming from, and then using this to triangulate a position..
> Cheers,
> Matt

Hi Matt,

Thank you for that detailed explanation. I am a DSP neophyte, but I am
absolutely interested in helping out in any way I can with this. In
fact, I just ordered a B200 with GPSDO from Ettus and will be
experimenting with it when it arrives.

I have read up on cyclostationary signals and am currently trying to
implement SPECCOA to determine a TDOA for multilateration.
Unfortunately, I am having difficulty understanding some of the math.
Are you familiar with SPECCOA, or do you know anyone I could talk to
off-list who can answer some questions I have?

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