Re: [Discuss-gnuradio] Moon Bounce Experiment

[Joseph Craig]

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

> 
>> 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?  

> 
>> 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.

> 
>> 4)  Is it possible to tweak parameters such as quadrature downconverter 
>> bandwidth/decimation, etc?
>> 
>> thanks,
>> Joe Craig
>> 
>> 
> 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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