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Re: [Discuss-gnuradio] Run USRP at alternate clock frequency?

From: Clark Pope
Subject: Re: [Discuss-gnuradio] Run USRP at alternate clock frequency?
Date: Fri, 31 Mar 2006 19:39:41 -0500

I'll try the heat gun solution first. (Gives me an excuse to buy one.)

Regarding the rational resampler: that is in software, right? I'm trying to run at 44 MHz so I can do the despreading for 802.11 inside the FPGA. I think I can do the differential detection in the fpga too so that the stream to the PC will just be the raw bits.

I've done some matlab simulations with good results using the USRP to collect off my own wlan. Even without an equalizer I'm getting near perfect packet reception.

Technically, if the packet rate is low enough I could do everything in software IF I put some smarts in the FPGA to only send the IF samples that belong to a packet. But net traffic would have to be less than a couple percent to be sustainable.


From: Matt Ettus <address@hidden>
To: discuss gnuradio <address@hidden>, Clark Pope <address@hidden>
Subject: Re: [Discuss-gnuradio] Run USRP at alternate clock frequency?
Date: Fri, 31 Mar 2006 16:02:35 -0800

Clark Pope wrote:
> I finally got my 44MHz oscillator in. Tried to remove the existing
> oscillator but I got nowhere with my iron and copper braid. Can anyone
> suggest a cheap tool that will allow me to get this surface mount
> oscillator up?

Nope.  Its tough unless you have a Metcal talon.  I would suggest that
you just cut the traces from the 2 pins on the left side and the one on
the right.  This will disable the oscillator, but would be very hard to

If there were a warranty, this would definitely void it :)

The USRP Rev 4's which are shipping now are much easier to run off an
external oscillator, but that won't help you.

By the way, we also have very good and fast rational resamplers in the
source.  Are you sure that wouldn't help you?


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