[linux-dvb] Re: Twinhan DST / TS204 and signal quality questions

[Manu Abraham <manu@kromtek.com>]

On Monday 16 Aug 2004 1:32 am, Johannes Stezenbach wrote:
> Werner Johansson wrote:
> > What seems strange about these Twinhan sat cards is that the signal
> > quality and strength indications seems very low compared to what I get on
> > my two regular STBs (one Philips/Canal Digital branded box and one Viasat
> > branded Thomson DSI-35TH). All the sat equipment is connected to a
> > Thomson SWID 98 C multiswitch fed with 4x2 signals from two quad LNBs
> > pointed at 1W and 5E. Having tried different ports on the multiswitch
> > they all behave the same, tried different cabling as well with no
> > difference.
> >
> > Also I have sat cards from two batches (one card with serial # starting
> > with 0312 and two consecutive numbered cards starting with 0401), both
> > giving the same results (roughly signal ~ 0x3c00 - 0x3d00 and snr ~
> > 0x1500 - 0x1900), which seems really low compared to the 80-90% quality
> > and strength I get from the STBs??
>
> If a STB displays a weak signal, what happens? Right, people call the
> support hotline and complain: "Why is my signal so bad? My Mom's
> STB gets a much stronger signal!"




		
		Is there something that we can do to measure the signal level output(using a 
spectrum analyzer) from the tuner ? Can we check the signal level from the 
inside stages of the tuner (Output stages of the TSA 5059/ ZARLINK SL 1952 or 
even a tap from the AGC of the STV0299) ?





> Solution from the marketing department: Adjust the scale of
> the displayed signal strength so it is always >80% (unless the
> signal is so bad that the picture suffers). Then both the
> customers and the support people are happy.
>




		What i have seen is that the signal quality/level what you receive on the 
Twinhan frontend is much lower than that of a conventional STB's. Even with 
conventional STB's in my region we have a problem with STB's that employ the 
tuner from LG. We have a low signal on the Hotbird 1,2,3,4,6 satellite. So 
therefore viewing Hotbird channels on a LG based STB is not a pretty good 
idea, unless you have a pretty large antenna, whereas you don't have any 
problems on Nilesat, Arabsat etc. I believe that's one of the reasons why LG 
STB's don't sell well in this region. The same goes for Samsung LNB's.


		The Twinhan tuners also behave much like the LG tuners when you have a bad 
signal. Even when i don't have a picture on the Twinhan card, i can watch the 
same channel on a conventional STB.




> On the driver level we don't bother, we just deliver raw register
> values and let the application do scaling/interpretation. The
> downside of this is that you cannot compare the numbers you get
> from different frontend hardware.



		It is right that at the driver level there's nothing that can be done, since 
it can only rectified by the company that manufactures the tuners (not the 
cards).

Regards,
Manu




> > The TS204 flag, would that imply that the Reed-Solomon FEC has not been
> > done on the card itself, or are the last 16 bytes of data just junk from
> > the correction process?
>
> It's junk.
>
> Johannes