Re: [Discuss-gnuradio] An interesting application for my new USRP... some input requested

[John Ackermann N8UR]

Larry Doolittle wrote:

[ snip ]
> In principle, you could dedicate a second channel to recording the
> GPS band, and extract near perfect frequency calibration from that.
> Unfortunately for your time-frame, GPS reception in itself is a
> serious project that has not been fully solved by the GNU Radio
> community (i.e., Krzysztof).
>
>
> > 2.  If I clock the USRP from a highly stable external reference, is 
> > there any other source of possible frequency error in the system (since 
> > we're at HF, I shouldn't need to use a downconverter)?  In other words, 
> > will the measured FFT frequency have any error source other than errors 
> > in the external reference?
>
>
> Not in the long term.  Any acquisition hardware adds phase noise,
> but that mostly averages away for the measurement you want to make.

Thanks for the response, Larry.  You're right that phase noise should 
average away over these time intervals.  I could also record a pilot 
frequency (ie, put 10MHz from my frequency standard) as part of the 
stream -- I did that at audio for the beat-note method I used in the past.

Actually, over these time intervals GPS wouldn't be as accurate as my 
local references -- assuming you're doing normal GPS time extraction, 
you need to get out to a few thousand seconds of averaging before GPS 
reaches its best accuracy.

I snipped your earlier comment about the data stream, but are you 
suggesting just capturing a single wide data stream instead of four 
discrete ones?  I was thinking that going with the four narrow channels 
would reduce the data transfer requirements, but if that's not an issue, 
what the heck...

Thanks again,

John