[linux-dvb] [RFC] SNR units in tuners

Andy Walls awalls at radix.net
Mon Oct 27 16:54:56 CET 2008


On Mon, 2008-10-27 at 15:03 +0100, Georg Acher wrote:
> On Mon, Oct 27, 2008 at 10:37:52AM +0000, Morgan Tørvolt wrote:
>  
> > As I used to work with satellite signals on an earth station, and was
> > responsible for the development of measurement techniques, I thought I
> > should join in here for some hopefully revelaing info.
> > 
> > I am guessing here of course, but I believe that there is no real SNR
> > measurement in any of the tuners available for computers. 
> 
> My guess is that it is possible. Actually, it is quite easy for QPSK ;-) You
> only need to calculate the distance of the IQ-value from the ideal symbol
> center ( (sqrt(0.5),sqrt(0.5)) or whatever) after the
> rotator/retiming-block.
> 

Isn't that just Error Vector Magnitude (EVM)?

<musing>
I suppose over a number of samples, EVM gives you an idea of the noise
power + source transmitter deformation, if the received signal remains
at a constant power.  I suppose you could estimate signal strength by
examining amplifier gain settings.
</musing>

Regards,
Andy




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