[linux-dvb] Re: DVB-C QAM128 errors and signal strength

[Jaakko Hyvätti <jaakko@hyvatti.iki.fi>]

On Wed, 6 Aug 2003, Jarkko Lavinen wrote:
> I am in HTV cable network in Helsinki.  I am able to tune and receive
> both QAM64 and QAM128 modulated frequencies.  The difference between
> these two is that QAM64 has little bit errors and no block errors
> whereas QAM128 has lots of bit errors and too many block errors to be
> usable.

  Jarkko dropped by last week and lended me the Siemens card.  I myself
have Technotrend ones, so this is an interesting test to see how the cards
perform with identical installation and signal.

  It seems my antenna signal is somewhat better, as my S/N is
significantly better and QAM128 streams display no uncorrected errors. I
modified my getfrontend.c <URL:http://www.iki.fi/hyvatti/dvb/> to give all
information the dvbtune -m gives, but you can use getfrontend while vdr is
running as it does not need exclusive access, just opens frontend read
only.

Jarkko, QAM128 stream:
>   +--------+--------+----------+----------+--------+
>   |        | Streng | Bit errs |      SNR | Uncorr |
>   +--------+--------+----------+----------+--------+
>   | avg:   |  65535 |   530000 |    57600 |     30 |

Me, another QAM128 stream:
$ getfrontend /dev/dvb/adapter1/frontend0
Signal=65535, Verror=11540, SNR=60138dB, QAM_128, FREQ=289.994239MHz,
SR=5.900000Msym, INV=OFF, BlockErrors=0, (S|L|C|V|SY|)

  So my SNR is considerably better, and I get Verrors at order of about
5000-10000, and no uncorrected errors.

  I would say it is the combination of a bit poorer antenna signal and
apparent Siemens unability to cope with it.  It is interesting that
another adapter, Hauppage, tuned to the same signal, does not display any
errors.  Verror=0, well maybe occassionally jumps to 10 but then goes
back.  S/N is reported by Hauppage to be a bit better too, around 61500
vs. Siemens 60000.

  I wonder if the rumours of Siemens having a better tuner are not true
after all.  Maybe it is just some parts of tuner that are good, or later
versions that now sell at 120 euros that are of degraded quality.  Or
maybe we can find QAM128 register settings that fix Siemens.

Jaakko

-- 
Foreca Ltd                                           Jaakko.Hyvatti@foreca.com
Pursimiehenkatu 29-31 B, FIN-00150 Helsinki, Finland     http://www.foreca.com


-- 
Info:
To unsubscribe send a mail to ecartis@linuxtv.org with "unsubscribe linux-dvb" as subject.