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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: Thu, 23 Feb 2017 23:55:38 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 02/23/2017 11:28 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.)

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,


Gnu Radio isn't "a radio with a lot of knobs". It's a specialized programming environment for *building radios*. You can do anything with it.

Just like you could, given a bucket of electronics parts of suitable diversity, build just about anything. But the parts by themselves just lie there, lifeless, until you, the programmer (or, you know solderer, to stretch a metaphor) breathe life into them.

You should be able to run gqrx at 250ksps, but I don't off the top of my head know how you configure that in gqrx, which is an *APPLICATION*
  that was partially built using the Gnu Radio framework.

Your question (to use a proximate metaphor) is like asking how to configure Visual Studio, with C#, to provide the functionality within
  Excel.   The answer would be "well, you'd program it to do so".

Gnu Radio is a programming environment, so, it's easy for the naive beginner to construct signal flows that are wildly suboptimal. Just like it's possible for the beginning C# (or Java, or Python, or C++) programmer to write code that, years hence, might not
  seem that wonderful.

I'd suggest spending some time in the "guided tutorials" section on the www.gnuradio.org website, and maybe curl up with a book on
  modern digital signal processing.

With Gnu Radio, there IS NO "what settings do I use to make my signal come out.".

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