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

[Juha <juhis@trinity.is-a-geek.com>]

Still slightly offtopic, but I'll give it a try. Would you happen to
know if this card:

http://www.usa-x.org/1shop/product_info.php?products_id=44&language=en

has the same tuner part as your techotrend card? The website says that
its got 'PHILIPS SAA 7146AH' and 'PHILIPS Vista VES1820-N70851.N1'
chipsets. Sounds like a good purchace if it has the same tuner as yours
and a bad one if it's not supported by linux-dvb ;)

TIA

Juhis


On Mon, 2003-08-11 at 10:54, Jaakko Hyvätti wrote:
> 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



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