sky+/HDTV confused?

[geebeeone]

I am just about to get a sky+ box and a HDTV TV. I have been reading the posts re-HDTV and am getting confused.
Will the current sky+ box be o.k. or will it have to be changed to the new one that is coming soon?

 

[Cupart]

Hi GeeBeeOne,

You won't be able to watch any HD channels through your Sky+ box (the picture will appear green and somewhat disorted) eventhough you have a HD television set. You'll be needing a new HD box (early 2006 from Sky) to be able to get the few channels on offer to begin with. There are non-Sky-HD-boxes available from mainland Europe but these won't be any use if you only want to watch Sky. You will also be able to watch SD (Standard Definition) channels on the new HD boxes.

Personally I would wait to get a new HD box as it will take some time before more channels will broadcast in HD and knowing Sky, there will probably be some software problems to start with...

Happy New Year...

:-hny

 

[geebeeone]

Thanks Cupart.
This is typical of Sky, pushing you to buy Sky + boxes but they don't tell you that you will have to buy another one when they start to broadcast HDTV.
I will definately wait to see what will be available when they do send HDTV.

 

[spiney]

Hi def tv broadcasts will be in the newer MPEG4 format - allowing much higher video compression, the whole point of it (!) - instead of the current MPEG2.

Transmission method (QPSK) is the same, so existing dish and cables are ok. However, the new video format requires an MPEG4 decoder, which doesn't exist inside current Sky receivers.

Connection to "hi def ready" tv screens will be via DVI/ HDMI interfaces. There might also be a SCART socket - and even UHF rf out - to also allow use of "ordinary" tv sets, but what's the point of getting hi def if you don't have the appropriate screen?

 

[waydownsouth]

Transmission method (QPSK) is the same, so existing dish and cables are ok. However, the new video format requires an MPEG4 decoder, which doesn't exist inside current Sky receivers

Well not quite correct, Sky's transmission on TP33 on Astra 2B is infact in 8PSK as per the DVB-S2 spec, not QPSK as used by DVB-S, that said your current dish/lnb is fine, just the STB needs replacing for one that supports DVB-S2, MPEG4 and HD frame formats.

DVB-S2 using 8psk gives roughly a 30% increase in throughput for the same transponder bandwidth, and MPEG4 allows acceptable 1080i pictures at 13Mb/s as opposed to 19Mb/s using MPEG2.

DVB-S2 has the added feature that it can be operated in a hieracical mode, that allows both QPSK and 8PSK transmissions simultaneously, thus older DVB-S stbs can see the qpsk traffic, but newer DVB-S2 stbs can see both transmissions, therefore it is possible for a transponder to carry all or near all of its old previously allocated SD payload for existing STBs and in addition carry a single HD channels payload for 8psk stbs. DVB-S2 allows for operation in either this hybrid method or for an even greater throughput in a 8psk only mode.

Cyril

 

[stealthpirate]

Geebee, you'll still be impressed with the Sky+ box, I think mines mint (hasn't broke yet ;) ) and I don't even like Sky!...... HDTV another subscription........MORE monieeeeeeeee for murdick.

 

[spiney]

thanks, Waydownsouth, for that info! I admit I didn't know that the modulation system was also changing. Fortunately, from what you say, it's not to a QAM system - which would decrease SNR and give some problems - but I'd have thought that increasing phase resolution would demand much higher demod standards inside the new receivers, not least much better clocking, etc.

Yes, I can see that "heirarchical mode" would be possible, and both combined on 1 transponder seems a good idea, must look up the details (when I've time ....).

(added) oops I'm wrong again (!), having just looked at some info on the new DVB-S2 standard at:

www.tandbergtv.com/pdfs/dvbinfo.pdf .

Is seems there's a large variety of different new modulation options - including QAM ones - but combined with newer fec error codings, to keep system SNR ("link margin") roughly the same!

(Simply going to QAM - with no other change - would of course lower the link margin, and 8psk will require better demod resolution inside the receiver!).

(Sorry, poor terminology, I should say "APSK", for combined phase/amplitude modulation, "QAM" is stricly the version used in DVB-T, for "Freeview" etc.).

 

[waydownsouth]

Although DVB-S2 does allow QAM options, the only ones that I am aware of that anyone is implementing is 8PSK, which is essentially just like qpsk but four more constellation points between each of the qpsk ones.

Cyril