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Re: [Discuss-gnuradio] Problem in using connect(gr.file_source, usrp.sin

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Problem in using connect(gr.file_source, usrp.sink_s)
Date: Wed, 25 Jul 2007 00:07:05 +0100
User-agent: Thunderbird (X11/20070604)

Eliane Hook wrote:
> Thanks for the responses.
> I have used twice the interpolation number as the decimation number
> that is
> used to record or receive the data.
> I did not understand this part:
> "Secondly, there is likely frequency offset between your original
> transmitter and the USRP on receive, as well as between the USRP on
> transmit and whatever receiver you're using.  Depending on what the
> modulation is you're dealing with, it might not survive these."
> I am using RFX2400 daughetr boards and am using 2.4G to transmit and
> recieve
> on the 2 boards. I am using gmsk modulation scheme.
> To answer this:
> "Are you not receiving the data back, or are you receiving nothing at all
> (power, distorted signal)? Is this a digital waveform? What are you
> doing for frequency synchronization?"
> I am not recieving the data back. I also used the oscope and checked the
> signal. It jus looks like noise but anything with gmsk modulation looked
> like noise to me.
> I did not understand what is meant by frequency synchronization.
The USRP's run with different clocks, start at different times, etc.,
etc., so the clocks are not synchronized and often need to be with some
phase lock loop technique or other synchronization method (see the comm
books by Proakis, Sklar, Rhode, or Ziemer  that discuss this topic, or
Gardner's book on PLLs).

But that's beside the point because you're using GMSK, which doesn't
need this and the M&M block tracks the symbol timing. So, sorry, back to
the starting point.

You should try using usrp_fft.py to see if there is any power being
received when you're transmitting.


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