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

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] weak signal detection in gnuradio / gqrx
Date: Fri, 24 Feb 2017 20:01:11 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 02/24/2017 07:16 PM, Cinaed Simson wrote:
On 02/23/2017 08:28 PM, Jon Elson wrote:

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

Thanks very much,


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