Re: [Discuss-gnuradio] OFDM behaviour of recent UHDs

[Vincenzo Pellegrini]

hi Josh,

thanks for the very prompt answer.

Will run the tests you suggest tomorrow morning (CET) and let you know.

As to the power, the receiver measures the very same received power value 

in both cases. You can see this from the (first from top) bar indicator on the instrument in the two pics.

regards

vince

2013/4/15 Josh Blum <address@hidden>

On 04/15/2013 03:39 PM, Vincenzo Pellegrini wrote:
> Hi everybody,
>
> I have been experiencing some difficulties in obtaining
> the same "signal clarity" performance that I used to have with
>
> uhd_003.004.000-f500b92
>
> when I tried to transmit the same samples of the same signal
> (also same usrp B100, same XCVR2450 front-end, same frequency =5.8GHz, same
> receiving device, same tx/rx antenna positions)
> with both:
>
> uhd_003.005.001
> and
> uhd_003.005.002
>
> at the following links you can find images of a DVB-T modulation analyzer
> exposed to both transmissions.
>
> www.pellegrini-radio.it/uhd_003.004.000-f500b92.jpg
> www.pellegrini-radio.it/uhd_003.005.002.jpg
>
> If you look at the MER value, a much poorer constellation quality is
> evident when operating with the newer UHD and its matched images.
> (no performance difference was noticed in this respect between
> uhd_003.005.001 and uhd_003.005.002).
>
> Has this been experienced before?
> As somethin changed in between that I should be aware of?
>

If 3.4.0 worked, I would definitely give 3.4.5 a try to see if any of
the patches or fixes could have inadvertently caused the issue. That
will at least narrow down which versions are causing the difference.

There was a fix to DSP scaling to prevent clipping. Its possible that
the power level is simply lower? What signal amplitude are you using,
and does doubling it solve the issue?

http://code.ettus.com/redmine/ettus/projects/uhd/wiki/ChangeLog#003004005

-josh

> my best regards to everybody
>
> vince
>
>
>

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--
Vincenzo Pellegrini
http://www.youtube.com/user/wwvince1