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Re: [Discuss-gnuradio] Negative values sent to usrp.sink_c ?

From: Lee Patton
Subject: Re: [Discuss-gnuradio] Negative values sent to usrp.sink_c ?
Date: Mon, 31 Jul 2006 17:12:39 -0400

On Mon, 2006-07-31 at 13:17 -0700, Matt Ettus wrote:
> Are you doing any carrier tracking?  

No I am not.  At the time I wrote the post, I didn't think I needed it
since my pulses came back looking pretty good except for the whole
"positive values only" thing.  However, my data looks a lot better when

a) use the tune() method instead of the set_freq() method to set the
carrier frequency.

b) find the carrier in the received data via an FFT, then modulate the
data down to DC. (essentially carrier tracking).

> Have you modified your RFX board to 
> be fully coherent?  I.e. disabled the onboard clocks as in
> http://comsec.com/wiki?USRPClockingNotes

No. I was hoping to avoid the extra phase noise that would be added (as 
in the webpage) by keeping the original configuration.  I can see now, that I 
might not be able to do that.


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