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Re: [Discuss-gnuradio] BURX 26MHz clock

From: David Evans
Subject: Re: [Discuss-gnuradio] BURX 26MHz clock
Date: Fri, 20 Aug 2010 06:47:50 -0700 (PDT)

Thanks John,

This is how I understood it, but I suppose my real question is (not being a dsp 
expert), why would you want to do this? 

I assumed that being a 26MHz clock, this would be ideal for GSM rate signals?


----- Original Message ----
From: John Orlando <address@hidden>
To: David Evans <address@hidden>
Cc: GNURadio <address@hidden>
Sent: Thu, 19 August, 2010 18:39:30
Subject: Re: [Discuss-gnuradio] BURX 26MHz clock

On Thu, Aug 19, 2010 at 12:17 PM, David Evans <address@hidden> wrote:
> Hi,
> Probably a stupid question...
> By connecting the BURX's 26MHz clock to the USRP2's 100MHz ref. input, as
> described in the source, does this pull the mainboard clock to 26MHz, or does 
> just phase lock to it? i.e. if I collect samples with usrp2_rx_cfile, these 
> all be samples at 26MHz?

On the USRP2, there isn't any way to provide an external clock source
(at least not a straight-forward way...you can always unsolder the 100
MHz oscillator etc).  So if you're interested in using the BURX's
on-board 26 MHz TCVCXO, this would clock the BURX board only, leaving
the A/D converters still running at 100 Msamples/sec.

The USRP2 can phase lock to an external 10 MHz reference, and it is
also possible (with firmware modifications to the aeMB code) to phase
lock to a reference clock frequency other than 10 MHz (this has been a
topic of discussion on the mailing list over the last week or so).  So
you can access the 26 MHz TCVCXO output of the BURX board through the
U.FL connector, and route it to the SMA input on the USRP2 where the
10 MHz reference typically goes, which will phase lock the two clocks.
But you will need to tweak the aeMB firware to make this happen.

John Orlando
CEO/System Architect
Epiq Solutions

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