[mythtv-users] SNR reported by kernel dvb for HD-5500 card

[Johan]

On Fri, 2008-04-04 at 10:04 -0400, Tom Dexter wrote:
> I'm using HD-5500 cards for OTA DTV.
> 
> Does anyone know if the signal to noise reported by the HD-5500 card
> is out of whack?  I think it almost has to be.
> 
> If I monitor it with femon from the media-tv/linuxtv-dvb-apps package
> I get what appears to be a correct signal strength (it usually jives
> with my Samsung HD receiver).  The snr however is never beyond the 8%
> to 13% range.  I can't believe it would even get a lock if that were
> correct:
> 
> femon -a 0 -h
> FE: LG Electronics LGDT3303 VSB/QAM Frontend (ATSC)
> status SCVYL | signal  94% | snr  12% | ber 00000000 | unc 00000000 |
> FE_HAS_LOCK

> 
> It'll appear like that when I'm getting flawless reception.
> 
> If I use the F7 key to bring up the signal monitor in my mythfrontend
> it'll show around 3.9dB.
> 
> My Samsung receiver only shows strength, not quality...and as I said,
> it jives with the above signal strength.  When I had my Sony
> DHG-HDD500 HD DVR I believe the quality usually showed 'good' or
> better.
> 
It's all down to how the registers of the receiverchips are read and
interpreted. Maybe this link can help you:
http://www.mail-archive.com/linux-dvb@linuxtv.org/msg20376.html

Actually, it's old enough to be implemented by now. Femon's method
reporting a percentage might not be correct. A SNR of 100% would mean
that Signal and Noise are equal, but in fact you have to interpret this
for femon as perfect. 
Is femon really using the driver (which reports in dB) or is it just
reading raw registervalues and making its own calculations...

If 8-13% works fine than that is your reference for a good reception.

Johan

> There's no way that's even close is it?
> 
> Tom