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

[Nick Foster]

On Thu, 2011-04-28 at 23:19 +0300, Stefan Gofferje wrote:
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> Hi,
> 
> On 04/28/2011 10:03 PM, Nick Foster wrote:
> >> 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.
> 
> Basically, we are just talking about good old analog FM narrowband radio
> com. MAYBE - as I said as a creamtip - ETSI DMR 2 Analog. But if nobody
> has written a trx yet, I guess, I have to forget about that. My
> developer skills are way out of that league. There might be a chance
> that I could get our boss to put out a bounty for that but I have to
> prove that the USRPs are what we need before that.

If you're just doing NBFM that's pretty braindead simple.

> 
> >> 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.
> 
> Marcus has already given me some pointers about the squelch / PTT thing.
> One thing however is not totally clear to me.
> A conventional radio has some "startup time" for the PLL to "swing in"
> when you start transmitting. How is that with SDRs or the USRP in
> specific? Does feeding data to the TX immediately result into a clear
> and stable signal or is there also some "swing in" time to consider?
> 
> Specifically, does one have to consider some prerun time of transmitting
> some "filler" before transmitting the actual payload?

Every time you tune the TX you'll have to wait a few ms for it to become
stable. For voice transmission purposes, a few ms is effectively
instantaneous anyway. And if you aren't retuning, then it will come up
instantly, because the LO will still be running in between sample
bursts.

--n

> 
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> 
> - -- 
>  (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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