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

From: Chris Stankevitz
Subject: Re: [Discuss-gnuradio] Losing data during long collects
Date: Wed, 04 Jun 2008 22:59:56 -0700
User-agent: Thunderbird (Windows/20070326)

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


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

Ahh, I see...

Thanks everyone,


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