Standards converter for "new" sets

[Studio263]

With the issue of running 405-line stuff now largely resolved does anyone have any ideas how to keep the newer sets going?

The problem is how does one generate a high quality signal to view on 625 line colour sets, complete with NICAM sound and teletext? Modulators in VTRs (etc) do a reasonable job but the sideband shaping is poor so the tuning never seems to be that sharp. The PAL encoding in DVD players / set top boxes never seems to be very good (it doesn't show the sets at their best anyway, with smeary colours often displaced from the objects that they are supposed to be part of), I've not seen a NICAM encoder (apart from the one in a certain very expensive Philips pattern generator) either and then there's teletext (the first ever digital home entertainment medium), will this just be forgotten?

Any ideas?

[ppppenguin]

Kat Manton's PC based approach to signal generation could generate any desired video signal including teletext but I don't think NICAM is possible this way. This approach uses an ordinary modulator. Direct Digital Synthesis has been discussed before and in theory could make any desired RF signal directly. Practice may be harder!

[Steve_P]

Cable TV stuff should do it. The head ends were full of modulators which would have carried Nicam + Teletext. Agile and Fixed Channel Types.

Taylor Brothers come to mind, along with Scientific Atlanta.

Taylor is here: http://www.taylorbros.co.uk/

There is a lot of stuff being chucked soon, I imagine!! One can only ask your local cable operator!!

Cheers,

Steve P

[David_Robinson]

There are quite a few digital satellite channels currently having the old-style teletext, e.g. Channel 5, CNN. How long this will last is anybody's guess. No NICAM though. As for modulators, I currently use a Sony SL-HF950 Betamax recorder for this and the quality of the modulator is excellent. For live pictures the modulator in my Humax PVR-9200T Freeview PVR is also very good. Still no NICAM though.

[DrZarkov]

Nearly all continental stations still have Teletext, there were attempts like MHP to change that, but they all flopped. So there is no chance that this will change in the near future. I (and many million other viewers in continental Europe) see why it should change. Sure not as long as the 625 line service continues.

[Studio263]

Originally Posted by DrZarkov

Sure not as long as the 625 line service continues.

This is the problem! Not long to go now, a life watching Freeview seems a bit grim compared to what you can now. I was thinking about multiple freeview receivers feeding into the existing aerial system for when the black day comes, but adding the NICAM modulation still seems to be the stumbling block.

Is there a freeview receiver that gives a better picture than the Sony one (VTX-D800U)? These are only available second hand now and look tricky to fix if they go wrong.

[Danny]

Hi i was chatting to a friend about this problem "what will happen when we whant to run txt sets in our collections " the humble G11 is now treated as part of tv history . we have been told that SVHS machines can record teletext but i havent tried this yet. I wonder if an encoder could be devised though. Danny

[stuie319]

Hi,

Playing back many VHS tape recordings sourced from terrestial broadcasts and switching to text will often show some semblence of teletext, from a garbled header with the date, to half pages. So I imagine its not unfeasable that a high bandwidth machine could save and resolve teletext. As for standards convertors for 625, other than text and nicam as mentioned, i'm puzzled by the objective. Digital sources already convert to 625 analogue at baseband which can be directly fed or modulated. When the day comes that direct analogue transmission stops, any convertor thereon would only be doing the job of todays DTT boxes, complete with digital artifacts. There would be no way of recreating true analogue PAL unless you did the whole chain from camera to reciever, or from tape surely. Does analogue distribution still exist or are tx feeds back converted to analogue from digital at source like 405 was?
ramble over i'll get me coat....

Regards Stu

[DrZarkov]

When I compare the signal of one of the few still existing bigger analogue transmitters in Germany with a digital satellite or DVB-T ("the german "Freeview") signal, the analogue signal is far superior! But this is only half the trues: In studios they are using digital equipment for many years now. There is no pure analogue TV any more since more than 20 years.

But back to converters: It should be just a question of software to generate a teletext signal using a PC. The other problem is that it will take only a few years until no graphic boards with analogue output will be available. Has anybody tried to buy a graphic board for the "hopeless oldfashioned" AGP slot, which is no longer in use since about 18 month?

[Studio263]

How about a way of downconverting HDTV into PAL? There must be enough data here to construct a decent picture without the blocks, jerks and limited colour pattete (3 x 8 bit) that Freeview (DTV) has? Is this technically possible?

[ppppenguin]

Originally Posted by Studio263

How about a way of downconverting HDTV into PAL? There must be enough data here to construct a decent picture without the blocks, jerks and limited colour pattete (3 x 8 bit) that Freeview (DTV) has? Is this technically possible?

This is done routinely in professional equipment. The quality of pictures downconverted from HD is often better than those originated at 625 lines. For example the entire Planet Earth series was originated in HD.

Professional TV equipment uses 3*10 bit colour components but there is very little loss with 3*8 bits if this is done correctly. The main reason for having 10 bits is to give headroom for multi-stage processing. AFAIK, no transmission system, current or proposed, uses more than 8 bit components.

Do not confuse the originated picture quality (often extremely good) with the artifacts caused by the transmission system. The extreme compression that is necessary for transmission will inevitably cause some visible effects. Sometimes (too often!) the compression is too great and the artifacts are too visible.

Remember that all TV transmission systems impose their own artifacts. Interlace, the original compression system, causes interline flicker effects. PAL has fuzzy colour and chroma/luma crosstalk problems that can be very visible. Both tehcniques were extremely good for their time.

I'm sure that when transmission systems are largely HD, there will be 625 outputs from the receiver boxes for many years.

[Andy Green]

Originally Posted by Studio263

The problem is how does one generate a high quality signal to view on 625 line colour sets, complete with NICAM sound and teletext?

Richard Russell's Test Card Generator also does Teletext -four pages at any one time. I Have one, and it is an excellent piece of kit - it also does just about all TV standards, and you can load a picture direct from a PC. (so complementing the Aurora nicely.

see rtrussell.co.uk

[dominicbeesley]

Hello, a few questions on this...

The teletext thing has been playing on my mind recently - especially when i visit places with freeview with its crappy, unuseable teletext replacement!

1) Does any one have or know where to find decent specs on how to transmit teletext. I'm going to set myself up at some point soon with an FPGA programmer setup and would like to do a teletext encoder as a first project.

2) Would anyone want a unit that
- plugs into PC via USB
- downloads RSS feeds
- makes a set of teletext pages
- unplug from usb
- plugs into back of telly to display the RSS info as a set of teletext pages?

3) Is all this stuff patent protected or is it an open standard?

4) Just an idea - any more ideas gratefully accepted!

5) No promises it may end up somewhere in the middle of the project pile for a long time!

Cheers

Dom

[murphyv310]

Originally Posted by dominicbeesley

Hello, a few questions on this...

The teletext thing has been playing on my mind recently - especially when i visit places with freeview with its crappy, unuseable teletext replacement!

1) Does any one have or know where to find decent specs on how to transmit teletext. I'm going to set myself up at some point soon with an FPGA programmer setup and would like to do a teletext encoder as a first project.

2) Would anyone want a unit that
- plugs into PC via USB
- downloads RSS feeds
- makes a set of teletext pages
- unplug from usb
- plugs into back of telly to display the RSS info as a set of teletext pages?

3) Is all this stuff patent protected or is it an open standard?

4) Just an idea - any more ideas gratefully accepted!

5) No promises it may end up somewhere in the middle of the project pile for a long time!

Cheers

Dom

Hi

the RT Russell test card generator has 4 page teletext built in and can be reprogrammed via the PC using RT Russells version of basic, its a great piece of kit.
trevor

[dominicbeesley]

Thanks for the reply, I understand that the converter is very good. But thats not really a _real_ teletext service. I'd like to build something that keeps teletext alive by doing something useful - 4 static pages is great for test / demo but not something you'd actually go and use on a daily basis.

Cheers

Dom

[Kat Manton]

Hi,

Personally, I find the picture quality of DVB-T on my somewhat tired 25" Mitsubishi Euro-12 to be significantly better than off-air PAL analogue. But I am feeding RGB into the SCART from a graphics card with 400MHz DACs, probably a little better than those in Freeview boxes and DVD players. The limiting factor is the bandwidth of the RGB drive circuitry in the set.

As Jeffrey says, there are artifacts with all systems. I think that after a time, our brains get used to one set of artifacts so, at first, trading one set of artifacts for another is noticable.

The brain is the best filter available but needs a little training. I can compare this with the 'problem' some younger people have with vinyl. I've known people born after the introduction of CD who've never heard vinyl; on first hearing it they can't listen through the surface noise, they're not as used to it as I am.

Sure, there are occasional artifacts on DVB-T but after watching it via the RGB input for some time now, going back to off-air PAL I find it looks fuzzy and washed-out and I really notice the low chroma bandwidth. What was once a pretty good picture is now unwatchable in comparison as I'm out of practice at filtering PAL artifacts; but I don't notice any artifacts with DVB-T now.

I'll also welcome HD broadcasts; apart from giving better 625-line pictures I should get rather better 819-line pictures on my 23" Sondyna than currently possible. I'm already keeping an eye on the price of Blu-ray and HD DVD drives, with one in the PC I should be able to demonstrate 819-line properly at long last.

Adding Teletext to the Linux/MythTV system is something vaguely on the list of things I may look into eventually. Rough thoughts on the matter; get text from somewhere (a user-selectable list of web pages, perhaps) and encode it, increase the number of lines in the X modeline, then add a filter to the MythTV system to add the teletext at the top of the image. It's just down to finding time to research it and write a bit more software.

Cheers, Kat

[ppppenguin]

Originally Posted by dominicbeesley

1) Does any one have or know where to find decent specs on how to transmit teletext. I'm going to set myself up at some point soon with an FPGA programmer setup and would like to do a teletext encoder as a first project.

3) Is all this stuff patent protected or is it an open standard?

AFAIK the teletext standard is open for anyone to use. I've got a poor quality photocopy of the original "White Book" standards document but the standard was subsequently enhanced so that an original "White Book" decoder won't display some pages accurately. The Wireless World decoder (1975/6?) had this problem.

I can see no huge problems in such a design. Kat's software based approach should work OK. A hardware approach, using programmable logic and a microprocessor should also work well. The MPU would format the data stream and send it to the FPGA. the FPGA would store the data stream in its internal RAM, serialise it put it on the right lines and add the teletext preamble etc. Also need a small amount of analogue circuitry to insert the text into the video. All pretty much routine design work for somebody like Darryl or myself though obviously a lot harder if you're not familiar with the technologies. Could use a processor core within the FPGA though I've never done this. If you google around you may even find that somebody has been there before and published their code.

I would probably start with something like the Xilinx Spartan 3A FPGA starter kit which I think has all the necessary digital functionality (no MPU, you'd need to use the Microblaze core).

[dominicbeesley]

I've built a fair number of things with uControllers and uProcessors, I'd now like a go at FPGAs. I'll probably go with a small Xilinx setup. Not sure what programmer to go for but I may build my own hanging off the back of an old BBC micro - just to make life a little harder!

For the analogue circuitry it looks like there are a number of options, I'll probably try with a simple analogue switch chip to start off with and see how it handles bandwidth.

Any info on the teletext standard gratefully accepted. So far my internet searching has not turned up anything more than a brief diagram from Wikipedia.

Cheers

Dom

[ppppenguin]

Originally Posted by dominicbeesley

I'll probably go with a small Xilinx setup. Not sure what programmer to go for but I may build my own hanging off the back of an old BBC micro - just to make life a little harder!

I hope that was a joke. You would have a serious struggle to make that work. The actual program for a Xilinx FPGA is held in an external PROM of some kind. Xilinx make it easy to use various serial and parallel flash devices. I have also used a lot of ordinary 27C040 EPROMs, usually with a microprocessor but sometimes alone.

The Xilinx kit I mentioned has built-in programming facilities via USB. For development work I usually use one of the Xilinx JTAG programming probes that attach to a parallel port. A later version works on a USB port.

Download the Spartan 3A data from the Xilinx website. Also documents ug331, ug332 and xapp986. Enjoy your bedtime reading

Originally Posted by dominicbeesley

For the analogue circuitry it looks like there are a number of options, I'll probably try with a simple analogue switch chip to start off with and see how it handles bandwidth.

The ordinary 74HC4053 is fine for video. Don't forget to clamp or DC restore the video ahead of it otherwise the black levels of the video and text won't match.

[arjoll]

Not sure if the info is any use (probably not!) but the DVB-S versions TV1/2 (TVNZ) and TV3 (Mediaworks) still broadcast teletext, and my satellite receiver outputs it quite happily to our Sony TV.

In other words I can switch to satellite, press the teletext button on the Sony remote and have teletext, just the same as with an analogue transmission. That's with a straight composite in to the Sony (the component in is used by the Media Centre).

I also get either Greek or Romanian teletext on one of the Optus B3 ethnic services but can't remember which

Surely there are some STB's available in the UK that output teletext?

As for NICAM it would just be a matter of getting a modulator to suit - I'm sure there are some around, but most of the 'stereo' modulators I see here are geared to the Australian market and use A2 not NICAM, so no use in NZ (or the UK).