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

[Alexandru Csete]

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