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

[Jon Elson]

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.)

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