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

From: Jon Elson
Subject: [Discuss-gnuradio] weak signal detection in gnuradio / gqrx
Date: Thu, 23 Feb 2017 22:28:56 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.1


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.)

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,


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