Re: [Discuss-gnuradio] weak signal detection in gnuradio / gqrx

[Marcus D. Leech]

On 02/24/2017 07:16 PM, Cinaed Simson wrote:
> On 02/23/2017 08:28 PM, Jon Elson wrote:
> > Hello,
> >
> > new user of gnuradio.  I'm still running on Ubuntu 12, so I installed a
> > virtual Ubuntu 14.04 guest with Virtualbox, as I couldn't get gnuradio
> > to compile on the Ubuntu 12 system.  The virtual 14.04 install seems to
> > run fine.  I have a
> > nooelec NESDR smart, rtl-sdr.
> >
> > I also have linrad installed on the Ubuntu 12 host, and it is able to
> > bring out weak CW on the 6m band.  (Don't have an upconverter, yet.)
> > There seem to be a couple guys on 6m that are sending slow Morse all day
> > long, and they generally give QUITE clear audio.  The CW is just visible
> > on the waterfall.
> >
> > So, I tried to tune them in with both gnuradio and gqrx.  Both just get
> > noise, and I can't see the signal on the waterfall of FFT graph.  Now,
> > one thing is that linrad is running my rtl at 200 KS/sec, and gnuradio
> > and gqrx seem to "like" over 1 MHz better.  If I try to select 200K
> > Sa/sec in gqrx, it doesn't seem to improve things any.  (Changing the
> > sample rate in gnuradio requires some tweaking of the decimation, so it
> > isn't one-click away.)
> In order to sample at 200 KS/sec with the RTL dongle you need to be able
> to write to the registers on the RTL dongle to select the sampling rate.
Also, 200ksps IS NOT an available sample-rate on the RTLSDR. 250ksps, 
and 300ksps are known to work, and
  then the next actually-works sample-rate is 900ksps.


> > Can anybody suggest some settings that help pull out the weaker CW
> > signals with gnuradio?
> >
> > linrad works better at weak signals, but the user interface is awful!
> > Another thing is that linrad uses only very little CPU resources, but
> > gnuradio loads my i5 CPU completely.  Does that have anything to do with
> > the virtual environment (virtualbox) or is it just the difference in the
> > software?
> >
> > Thanks very much,
> >
> > Jon
> >
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>
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