[USRP-users] USRP1 and UHD rx_samples_to_file

Jason Abele jason at ettus.com
Mon Nov 15 14:03:35 EST 2010


On Mon, Nov 15, 2010 at 11:47:33AM -0500, Steven Clark wrote:
> On Fri, Nov 12, 2010 at 10:41 PM, Steven Clark <steven.p.clark at gmail.com>wrote:
> 
> >
> >
> > On Fri, Nov 12, 2010 at 7:23 PM, Josh Blum <josh at joshknows.com> wrote:
> >
> >>
> >>
> >>> The amount of data written to the file is correct. HOWEVER, the output
> >>> written to test.bin looks wrong. It is mostly in range [-4,4], with some
> >>> large amplitude junk at the beginning of the capture. I don't see
> >>> anything
> >>>
> >>
> >> probably just noise
> >>
> >>
> >>  resembling a sine wave. When I capture with the same input using
> >>> GNURadio, I
> >>> see a nice fat sine wave as expected. Any ideas?
> >>>
> >>>
> >> was this with gnuradio + uhd?
> >>
> >>
> > the working capture was with old (non-uhd) drivers.
> >
> >
> >> do you have both slots populated on the USRP1? If so, the UHD may be
> >> selecting the wrong board via some default behavior), can you try it with
> >> one populated?
> >>
> >> try running the the ascii dft with the same options and see if the tone is
> >> present.
> >>
> >> -josh
> >>
> >
> >
> > I had 2 WBXs in the USRP1, but regardless of which one I fed input to, UHD
> > collect looked the same (low level noise + startup junk). I will try taking
> > one WBX out / the ascii thing on Monday back at work.
> >
> > Thanks again for your patient help!
> >
> > -Steven
> >
> 
> I tried removing one WBX and recapturing, and also using the ascii dft
> program. None of these approaches showed my tone. And again, switching back
> to gnuradio + non-uhd drivers worked fine (showed nice beefy tone). Any
> ideas?
> 
> ./rx_ascii_art_dft --rate=250e3 --freq=433e6
> linux; GNU C++ version 4.4.4 20100630 (Red Hat 4.4.4-10); Boost_104100;
> UHD_20101109.230702.c0dfc2c
> 
> 
> Creating the usrp device with: ...
> Using Device: Single USRP:
>   Device: usrp1 device
>   Mboard: usrp1 mboard - 4c7560d7
>   RX DSP: usrp1 ddc 2X + hb
>   RX Channel: 0
>     RX Dboard: usrp1 dboard (rx unit) - A
>     RX Subdev: WBX (0x0053)
>   TX DSP: usrp1 duc 2X
>   TX Channel: 0
>     TX Dboard: usrp1 dboard (tx unit) - A
>     TX Subdev: WBX (0x0052)
> 

Steven,

The UHD and libusrp1 drivers from GNUradio have different default gain
settings.  UHD defaults to 0dB and libusrp1 defaults to mid-gain, which
I think will be around 25dB.  These give very different Noise Figures
for WBX.  Try the rx_ascii_art_dft with --gain=25

Jason




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