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Re: [Discuss-gnuradio] Cross band relais / bridge - DMR?

From: Nick Foster
Subject: Re: [Discuss-gnuradio] Cross band relais / bridge - DMR?
Date: Thu, 28 Apr 2011 12:03:58 -0700

On Thu, 2011-04-28 at 21:37 +0300, Stefan Gofferje wrote:
> Hash: SHA1
> Hi,
> would any of the USRPs together with gnuradio be suitable to serve as a
> configurable cross band relais?
> I sometimes have applications where we have to communicate which huge
> amounts of radio systems which are not ours, which means that we either
> have to give out a whole bunch of radios from us (and we don't have so
> many) or work with the radios of the other party (which is not always
> desireable).
> A very nice thing would be a cross band relais which would transmit
> whatever is received from one of the channels on the other channel.
> Simplex would absolutely suffice.

Without any details at all on what systems you're trying to communicate
with, the answer is "very probably, but you'll have to do it all
yourself". In other words, the hardware when used with Gnuradio will
generate and receive pretty much any signal less than [25MHz for N210,
8MHz for USRP1, ~4MHz for E100] wide. But you're going to have to
implement the whole transceiver system yourself, and that's not a
plug-and-play proposition by any stretch of the imagination.

You may need to have complete details of the protocols used for each of
the systems you plan to communicate with, especially if you plan on
operating/receiving a trunk. In the case of some of the protocols
(Motorola Smartnet, LTR Multinet, EDACS) the standards are not publicly
available, and lots of reverse-engineering will be involved in
successfully getting Gnuradio to communicate with these systems.

> I have been working my way through grc but I am not absolutely clear how
> to realize the squelch/PTT logic. Of course, I don't want the box to
> xmit continuously but only if an actual signal is received. There also
> has to be some lockout-logic, so the relaying only goes in one direction
> at a time. Otherwise, we would have a nasty feedback :).

This is readily accomplished with existing Gnuradio blocks when combined
with Python code for the main application. You may or may not be able to
get such a system working entirely within GRC. There are multiple
existing squelch blocks based on tone decoding and/or receive power
level. I've been meaning to put in an "FM quieting" squelch like COTS
handheld FM radios use, but haven't gotten around to it. Power squelch
works fine for most uses.

> The creamtip would be if gnuradio would speak ETSI DMR but I also didn't
> find too much about that yet...
> We plan to change to DMR somewhat soon but most partners/customers still
> use analog radios...

Gnuradio is certainly capable of speaking ETSI DMR. Nobody has written
such a transceiver for Gnuradio, so if you're willing to do the legwork,
it would be a welcome addition to the platform. It would definitely
involve writing your own C++ signal processing blocks as well as Python
code to glue them together.


> Any hints?
> - -S
> - -- 
>  (o_   Stefan Gofferje            | SCLT, MCP, CCSA
>  //\   Reg'd Linux User #247167   | VCP #2263
>  V_/_  Heckler & Koch - the original point and click interface
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