[op25-dev] Re: In need of signal samples

Matt D md123 at nycap.rr.com
Mon Apr 1 02:35:11 UTC 2013


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On 03/31/2013 07:22 PM, souf308 wrote:
> OK I think I actually found out how to use the info file. But I
> still need some help to configure the parameters in the OP25.grc
> and use the samples (sorry to bother you with those beginners
> questions) ---------------------------- Here is the info file (from
> the website) (dp0 S'capture-rate' p1 I250000 sS'source-decim' p2 
> I256 sS'source-dev' p3 S'USRP' p4 sS'center-freq' p5 F434075000.0 
> s. --------------- So * 'capture-rate' corresponds to the parameter
> 'samp_rate' in grc file hence samp_rate=250000
> 
> * 'center frequency'=434075000.0
> 
> *but what about 'channel_rate'? (=250000?)
> 
> *In this formula (channel_rate/(2.0 * math.pi *
> op25.SYMBOL_DEVIATION)) what is op25.SYMBOL_DEVIATION???
> 
> *what is samp_per_sym??
> 
> Thanks in advance for you help
> 
> Souf
> 
Hi Souf,
yes the capture rate is the sample rate. sample per symbol is what
changes the channel rate, don't change the channel rate directly; I
believe the channel rate should be between 19.2k and 43.2k.
decimation changes the pre_channel rate, looks like he had it set at
256.
I have found that it is best to play a file is with the flow graph set
exactly as it was set when the file is captured.  If you want to have
a go with a capture I made I put the file up for download at:
http://www.fileswap.com/dl/9kfgeOXMz/
I think the frequency, sample rate, decimation, and symbol_per_sample
information is in the tar file.  put a throttle right after the file
source or the file will play in about 11 seconds instead of the real
speed of about 40 seconds.  so when you play the file first you tune
to the frequency, next on the BB-1 tab you wait for the carrier freq
to pop up, then go to the X-late1 tab and use the offset to get the
channel at zero and narrow the bandwidth with the xlateBW slider, then
go to the Dbits tab select autorange and change the marker to dots.
you'll see the dots go from scattered into 4 perfect lines and you'll
hear the transmission.
Thanks

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