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Re: [Discuss-gnuradio] changing the vctcxo

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] changing the vctcxo
Date: Thu, 8 Mar 2007 16:29:26 -0800
User-agent: Mutt/1.5.9i

On Thu, Mar 08, 2007 at 03:54:15PM -0800, Hans Glitsch wrote:
> Hi,
> Thanks for the replies.
> Yes, I have had it working with the rational resampler, but I'm trying to 
> eliminate that block.  I'm eventually going to use a very low power, 
> fanless pc to run the software, so we're trying to shave off as many cycles 
> as possible.
> I attached an external signal generator at 38.4MHz and decimated by 250 to 
> get down to a sample rate of 153.6KHz per channel (we use four rx 
> channels). This works well, gives the needed bandwidth, and lowers the usb 
> data rate down to a minimum.  If I can replace the vctcxo for a few dollars 
> and eliminate this block, then I think it's worth it.

Makes sense.

> I just found this one on Digikey: 
> http://www.abracon.com/Oscillators/ASVTX11.pdf
> I'm not an experienced hardware guy, but it looks like it would work in the 
> usrp.  Please tell me if I'm wrong.
> Thanks,
> Hans

Have you tried using oprofile to determine where the hot-spots are in
the code?  http://oprofile.sf.net

In some of our other code we've noticed that substantial time is being
consumed computing sin and cos in some NCOs.  That's one of the next
places we're looking at addressing with some SIMD assembler.


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