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Re: [Discuss-gnuradio] OFDM Transmiter and receiver by using USRP1

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] OFDM Transmiter and receiver by using USRP1
Date: Tue, 18 Oct 2011 14:18:03 -0400
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20101027 Fedora/3.0.10-1.fc12 Thunderbird/3.0.10

> hi Marcus,
> I am attaching the screen shots and also block diagram of transmitter..
> right now i am just trying to look for transmission of OFDM signal via
> usrp1. As i mentioned earlier in the fft scope plot in gnu radio i see the
> typical ofdm signal but on the other hand in usrp sink on the spectrum
> analyser i saw only simple sine wave peak. please have a look and let me
> know if there is something else do i need to do to generate the proper ofdm
> signal on the spectrum analyser.
> /home/hp/Desktop/spectrumoutput.jpeg 
> http://old.nabble.com/file/p32675018/spectrumoutput.jpeg spectrumoutput.jpeg 
> Block diagram in GNU radio
> /home/hp/Documents/finaltesting.grc 
> http://old.nabble.com/file/p32675018/finaltesting.grc finaltesting.grc 
Your flow-graph appears to be badly confused about bandwidths and
interpolations and sample rates
  --an interpolation ratio on your USRP1 sink of 100e6 is almost
certainly *not* what you had in mind.

You probably need to learn more about all of that, and get some better
notions of how the OFDM
  modulator block works.  At the very least you'll need to
fractionally-interpolate the baseband
  up to some sample rather that *can* reasonably be further interpolated
by the USRP1 hardware.

Given how simple this graph currently is, I'd *strongly* suggest that
you upgrade your "world" to UHD,
  since your investment in the "old world" is still rather small.

Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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