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From: | emilio gonzalez |
Subject: | Re: [Discuss-gnuradio] working with WFM sample data |
Date: | Wed, 15 Feb 2012 11:05:31 -0800 |
User-agent: | RoundCube Webmail/0.5.2 |
hi Marcus,thanks for this tip, it pushed me the the right direction. i guess this capture file isn't the standard "complex" datatype, and a conversion was the answer. i found the answer on the gnuradio.org Octave page that said the magic word, short. i use this graph to render on an FFT scope:
[ File Source (short) ] -> [ Throttle (complex, 25M) ] -> [ IShort to Complex ] -> [ FFT Scope (complex, rate 25M) ]using IShort to Complex was just a result of experimentation, as Short to Complex seemed to output only half the captured band. now i get to delve in to the world of filters, oof!
i'm surprised this isn't listed on the gnuradio.org Sample Data page ( http://gnuradio.org/redmine/projects/gnuradio/wiki/SampleData ), as i've come across messages from other folks confused about the data types and semantics of these USRP capture files. i suggest an addition to that page that mentions the necessity of an IShort conversion.
thanks again! - emilio KI6NVO
It's very likely that your on-disk sample format isn't what you've declared to Gnu Radio, and it's seeing some garbage numbers. Is it possible that it's stored as 16-bit I 16-bit Q in the file? If so, you'll need to convert it before any of your complex-float blocks do anything with it.
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