Re: [Discuss-gnuradio] Losing data during long collects

[Chris Stankevitz]

Eric Blossom wrote:
> What evidence do you have that data is being dropped?

Eric,

I know data is missing from my recorded file because the C/A code of 
every GPS satellite in my collection jumps by an unexpected amount.  The 
C/A offset for GPS satellites should increase 1024 "chips" every ms. 
Holes in GPS data are unmistakable -- and I had been dealing with them 
for months before I got a new hard drive setup.

However, just because the data is missing from the file doesn't mean 
there is a problem with the USRP.  For example, my data writing routine 
can insert some junk into the file (e.g. I write an error message out to 
stdout along with the USRP bits vs to stderr).  Or I could have fouled 
up the buffer or threading.

USRP's cfile utility cannot write my data without overruns, so I use my 
own app which I have attached to this email in case anyone is 
interested.  I will try Juha's recorder to see if it performs better.

> Can you hook up a siggen and feed a single sinusoid to the USRP rx
> daughterboard?  Tune the USRP so that the sinusoid is not at DC in the
> complex baseband, and log that data using your program and/or
> usrp_rx_cfile.  Then use octave or some other tool to look for
> discontinuities in the received signal.

I will perform this test; however, I expect I will see the same results 
since GPS provide me with quality sinusoids.

> This would allow you to confirm or refute the existence of the
> discontinuity using a much less complicated detector than your GPS
> receiver.

Ahh, I see...

Thanks everyone,

Chris

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