[Discuss-gnuradio] Re: USRP - No quadrature samples

[Nick Withers]

On Mon, 2009-06-29 at 19:43 +1000, Nick Withers wrote:
> G'day everyone,
> 
> I'm a bit worried... I no longer seem to be able to get anything but
> zeroes on the quadrature channel out of gr-radar-mono (and my derived
> wind profiler code).

I've attached an image of a plot of the in-phase samples received from
my wind profiler code... It may well be horribly misleading, given that
it's highly pre-alpha stuff, but it might also give someone a clue.
Certainly looks bizarre to me! Looks like a mix of the real and
quadrature samples I want / am expecting to see (~10 kHz wave; we're
sampling over 0.2 ms), along with their sum(?) and some zeroes thrown in
for good measure.

But yeah, this may not actually be as a result of the same problem, but
more my in-development work.

> (Warning: This is pretty much all FPGA-side code)
> ____
> 
> Short version: I seem to be getting only zeroes for quadrature samples.
> Could this be a software problem? Have I mucked up my hardware?
> 
> I'm using a USRP rev. 4 with a BasicRX. GNUradio 3.2, Ubuntu 9.04.
> ____
> 
> I get quadrature "samples" as expected if I run with debugging ("-D"
> flag to usrp_radar_mono), which chucks through FPGA-generated data. If I
> modify my wind profiler code to throw quadrature samples to both the
> real and imaginary output channels, I get nothin' but zeroes on both
> real and imaginary.
> 
> I'm examining data by using read_complex_binary
> (gnuradio-core/src/utils/read_complex_binary.m) and plotting with
> "plot(real(samples))" / "plot(imag(samples))" in GNU Octave.
> 
> It's taken me a while to notice this problem and a couple of things have
> happened lately that may be related:
>   - I've physically moved my USRP / PC / signal generator; and
>   - I've updated over a hundred packages on the Ubuntu 9.04 PC to bring
> it up to date.
> 
> Could this be a software issue? From looking at synaptic it did look
> like I had registered GNUradio / USRP packages (libgnuradio, libusrp,
> etc.), which I imagine I had installed yonks ago before I'd built
> GNUradio from SVN. I've tried removing all those and rebuilding GNUradio
> 3.2 from scratch, but the problem persists. I can rebuild the box, but
> if it's just gonna reinstall the same required libraries and so forth
> that I may be having a problem with it may not give me very helpful. I
> can rebuild the box with another OS but I'm trying to stay as boring and
> mainstream as possible.
> 
> ...Or maybe I've stuffed my USRP hardware? I'm working almost
> exclusively in the FPGA...
> 
> If someone with an up-to-date Ubuntu 9.04 machine with GNUradio 3.2
> could try to reproduce this I'd owe them a beer!
> 
> Any pointers appreciated, cheers all!
-- 
Nick Withers
email: address@hidden
Web: http://www.nickwithers.com
Mobile: +61 414 397 446

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