Re: [Discuss-gnuradio] GNURadio -> UHD transition LFRX (Ubuntu, Karmic)

[john]

On Tue, 2010-12-28 at 00:56 +0100, Alexandru Csete wrote:
> On Tue, Dec 28, 2010 at 12:33 AM, john <address@hidden> wrote:
> > I have migrated to UHD and leaving the rest of the plumbing as is, I
> > have the attached USRP block which works but when I put the UHD block
> > attached, it does not without any error diagnostics.
> >
> > Sometimes the FFT scope works showing the peaks of local radio stations,
> > but I never get any audio.
> >
> > Anything obvious? I wonder if it is the type of the signal on UHD but
> > have no more than that hunch.
> >
> 
> John,
> 
> I suspect the signal strength is too low - I mean the magnitude of the 
> samples.
> One significant difference between UHD and the old driver is the
> numerical range of the samples. The old driver used signed integer
> range with samples between +/- 16000 or so, while UHD uses +/- 1.0. In
> practice I often see samples far below 0.1. For FM and PM it is no big
> deal but for AM-type radio this is just too low because the dynamic
> range of the soundcard is also +/- 1.0. You can use a scope sink
> connected to the UHD source to see the range of the samples you are
> getting and put in a "multiply with constant" block to increase the
> signal to sufficient level.
> 
> Alex
> 
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Thanks Alex,
           You are correct. I needed to put in a complex multiply
constant of ~75,000 to get similar levels on FFT under UHD compared to
USRP.

           Thanks again,

                 Kind Regards,

                       John