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

From: Cinaed Simson
Subject: Re: [Discuss-gnuradio] weak signal detection in gnuradio / gqrx
Date: Fri, 24 Feb 2017 16:16:47 -0800
User-agent: Mozilla/5.0 (X11; Linux i686; rv:45.0) Gecko/20100101 Thunderbird/45.7.1

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.

> 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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