# GNURadio -\> UHD transition LFRX (Ubuntu, Karmic)

**URL:** <https://www.ruby-forum.com/t/gnuradio-uhd-transition-lfrx-ubuntu-karmic/201003>\
**Category:** GNU Radio\
**Created:** [December 28, 2010, 12:40am UTC](https://www.ruby-forum.com/t/gnuradio-uhd-transition-lfrx-ubuntu-karmic/201003 "2010-12-28T00:40:06Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![luislavena](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/0ea827/32.png) [@luislavena](https://www.ruby-forum.com/u/luislavena)\
**Post date:** [December 28, 2010, 12:40am UTC](https://www.ruby-forum.com/t/gnuradio-uhd-transition-lfrx-ubuntu-karmic/201003/1 "2010-12-28T00:40:06Z")

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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).

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**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [December 28, 2010, 12:57am UTC](https://www.ruby-forum.com/t/gnuradio-uhd-transition-lfrx-ubuntu-karmic/201003/2 "2010-12-28T00:57:40Z")

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On Tue, Dec 28, 2010 at 12:33 AM, john [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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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<div class="post-metadata">

**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [December 28, 2010, 2:25am UTC](https://www.ruby-forum.com/t/gnuradio-uhd-transition-lfrx-ubuntu-karmic/201003/3 "2010-12-28T02:25:50Z")

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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

```

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<div class="post-metadata">

**Author:** ![john\_old](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/9f8e36/32.png) [@john\_old](https://www.ruby-forum.com/u/john_old)\
**Post date:** [December 28, 2010, 5:46am UTC](https://www.ruby-forum.com/t/gnuradio-uhd-transition-lfrx-ubuntu-karmic/201003/4 "2010-12-28T05:46:02Z")

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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
> 
> * * *
> 
> Discuss-gnuradio mailing list  
> [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
> [Discuss-gnuradio Info Page](http://lists.gnu.org/mailman/listinfo/discuss-gnuradio)

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

```