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

[Tom Dexter]

On Fri, Apr 4, 2008 at 10:04 AM, Tom Dexter <digitalaudiorock at gmail.com> 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
>  status SCVYL | signal  96% | snr  13% | ber 00000000 | unc 00000000 |
>  FE_HAS_LOCK
>  status SCVYL | signal  93% | snr  12% | ber 00000000 | unc 00000000 |
>  FE_HAS_LOCK
>  status SCVYL | signal  98% | snr  13% | ber 00000000 | unc 00000000 |
>  FE_HAS_LOCK
>  status SCVYL | signal  93% | snr  12% | ber 00000000 | unc 00000000 |
>  FE_HAS_LOCK
>  status SCVYL | signal  96% | snr  13% | 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.
>
>  There's no way that's even close is it?
>
>  Tom
>

According to a user on the pcHDTV forum, you can get the approximate
s/n of the HD-5500 in dB my dividing the raw number reported by 256.
For example, if I run femon without the 'human readable' option I get:

femon -a 0
FE: LG Electronics LGDT3303 VSB/QAM Frontend (ATSC)
status SCVYL | signal bb79 | snr 19a1 | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status SCVYL | signal bfd8 | snr 1a3a | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status SCVYL | signal adb3 | snr 17bf | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status SCVYL | signal a19d | snr 1618 | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status SCVYL | signal c322 | snr 1aad | ber 00000000 | unc 00000000 |
FE_HAS_LOCK

I can divide that snr hex value by 256 to approximate s/n in dB, as in
this version of femon I just altered:

femon -a 0 -h
FE: LG Electronics LGDT3303 VSB/QAM Frontend (ATSC)
status SCVYL | signal  75% | s/n  26dB | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status SCVYL | signal  63% | s/n  22dB | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status SCVYL | signal  67% | s/n  23dB | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status SCVYL | signal  61% | s/n  21dB | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status SCVYL | signal  69% | s/n  24dB | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status SCVYL | signal  57% | s/n  20dB | ber 00000000 | unc 00000000 |
FE_HAS_LOCK
status SCVYL | signal  64% | s/n  22dB | ber 00000000 | unc 00000000 |
FE_HAS_LOCK

Now that makes much more sense.

Tom