Re: [Discuss-gnuradio] Moon Bounce Experiment

[Nick Foster]

On Wed, 2010-10-20 at 18:49 -0600, Joseph Craig wrote:
> Hi Marcus,
> 
> Thanks for the quick reply...
> 
> 
> On Oct 20, 2010, at 5:51 PM, Marcus D. Leech wrote:
> 
> > On 10/20/2010 07:13 PM, Joseph Craig wrote:
> >> I have managed to install gnuradio and run usrp_fft.py with success!
> >> 
> >> Now for the questions...
> >> 
> >> 1)  I'm always seeing...  "Exception RuntimeError: 'maximum recursion 
> >> depth exceeded while calling a Python object' in <type 
> >> 'exception.AttributeError'> ignored ".  What does this mean, and how to 
> >> fix it?
> >> 
> > In what application are you seeing this error?
> 
> python

I think Marcus is asking which Python application you are seeing the
exception in. Is it in usrp_fft.py?

> 
> > 
> >> 2)  How do I save the I/Q stream to disk?  I'm interested in the maximum 
> >> bit resolution for the best dynamic range.  I just want the raw time 
> >> samples.
> >> 
> > You should investigate gnuradio-companion (GRC), which allows you to put
> > a signal processing
> >  graph together graphically--like LEGO building blocks.  You can very
> > easily put together a
> >  "baseband recorder" application in about 5 minutes this way.
> 
> 5 minutes is pretty enticing seeing how this has to be working friday.  How 
> long does it take to setup GRC?  Is there a guide?  
> 

You can also use usrp_rx_cfile.py to save the raw complex stream to
disk. The help info for that file is pretty self-explanatory. However,
GRC is very very useful for putting together flowgraphs quickly. Follow
the Gnuradio build guide to get GRC built.

> > 
> >> 3)  Some of the examples (like usrp_wfm_rcv.py) spit out 
> >> "...aUaUaUaUaU..." to the console and the sound is choppy.  What does this 
> >> mean, and is there a way to turn it off?
> >> 
> > It means that you're experiencing a audio underrun, likely because your
> > processing chain
> >  can't "keep up".  Perhaps because you haven't specified a high enough
> > decimation, and
> >  the chain is trying to keep up with a unpleasantly-large torrent of data.
> 
> ah, yes.  should have thought of this.  I will check out increasing the 
> decimation.

You might also have the infamous "two-clocks" problem, which I won't
explain in detail here. But basically the soundcard clock might not be
exactly what it says it is, and if it's off enough from what the
flowgraph assumes it is, you will drop samples or underrun depending on
which way the error lies. We really need a better sound driver in GR and
if I ever see free time again I'll be working on it.

Nick

> 
> > 
> >> 4)  Is it possible to tweak parameters such as quadrature downconverter 
> >> bandwidth/decimation, etc?
> >> 
> >> 
> > Yes, absolutely.  Most of the example programs take a "-d" option that
> > controls decimation
> >  in the USRP hardware. For example, if you only wanted 1MHz bandwidth,
> > you'd use a
> >  "-d" option to the examples (like usrp_fft.py) of "-d 64", which will
> > give you 1Msps of
> >  complex samples between the USRP and the host--because the A/D in the
> > USRP is
> >  64Msps.  For the USRP2, the A/D operates at 100Msps, so you'd need to
> > adjust your
> >  decimation appropriately.
> 
> Got it!
> 
> > 
> > You should keep in mind that except for trivial algorithms at modest
> > bandwidths, you'll need
> >  a fairly-decent computer to get the best results from your Gnu Radio
> > experiments.  Although
> >  I think you mentioned that at first you only want to record baseband
> > data to disk at 1Msps,
> >  I'm guessing you'll want to go beyond that at some point.
> 
> it's a year old linux box we were using for fairly high bandwidth recording 
> from ethernet, so it should be ok.
> 
> Joe
> > 
> > I'd explore gnuradio-companion as well.
> > 
> > Good luck!
> > 
> > -- 
> > Principal Investigator
> > Shirleys Bay Radio Astronomy Consortium
> > http://www.sbrac.org
> > 
> > 
> > 
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> 
> 
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