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Re: [Discuss-gnuradio] working with WFM sample data

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

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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