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

[Josh Blum]

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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