GNURadio -> UHD transition LFRX (Ubuntu, Karmic)

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.

   Kind Regards,

              John

p.s. I know that switching back and forth between UHD and USRP
sourced-GRC will likely cause f/w issues particularly for the latter (in
that UHD seems to load on the fly).

On Tue, Dec 28, 2010 at 12:33 AM, john [email protected] 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

On Tue, 2010-12-28 at 12:33 +1300, john wrote:

   Kind Regards,

              John

p.s. I know that switching back and forth between UHD and USRP
sourced-GRC will likely cause f/w issues particularly for the latter (in
that UHD seems to load on the fly).

After looking at the output level on the FFT on the UHD, I realised it
was way too low compared to the USRP implementation.

The final solution was to complex multiply the output of the UHD block
by 75,000.

Josh had mentioned the output level of UHD but it didn’t twig that I
would need a multiplier.

Kind Regards,

        John

On Tue, 2010-12-28 at 00:56 +0100, Alexandru C. wrote:

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