Moderators: Dave Moll, Andrew Davie, Steve Anderson
there are people who advertise 625-405 line conversion services in the magazine "405-Alive", details of which are on the preceding page.
ppppenguin wrote:Optical conversion works OK. Point a 405 camera at a 625 monitor. Not as good as electronic conversion but adequate. I've done it the other way round to recover 405 tapes where there isn't currently an electronic solution available off the shelf. Darius's analogue 625 to 405 converter was a remarkable piece of design, using CCD chips originally designed as 1 line delays for colour TVs. Bandwidth is limited and parts are hard to get. You'd want to be pretty dedicated to follow in his footsteps.
Experimenting is fine and good. Just to prove the point I've built a 625 to 405 converter using boards left over from a professional design job. Basically a decoder chip, FPGA, SDRAM and DAC. It works very well.
But if you just want to run your 405 sets with best possible picture quality then an Aurora is well worth the price.
Harry Dalek wrote:I recall seeing a photo in electronics Australia on a 70s 525 line 625 line converter for a tv station here must of been made all via transistors the case was the length and size of a wall .
ppppenguin wrote:That would be the CO6/508 analogue field store converter designed by the BBC and made under licence by Pye. The prototype was ready just in time for he 1968 Mexico olympics when live coverage by satellite was feasible. Until then conversion between different field rates could only be done optically.
There's a photo of the beast in that report. I may have some other photos somewhere.The main stores were polygonal prism ultrasonic delay lines, like a PAL delay line on steroids. Some logic chips were used in the design. Probably RTL or DTL as TTL was very new indeed back then.
The main reason I built a 625 to 405 converter was just to prove the point. I'd been writing about the subject for some and felt I ought to prove that I could do it. Since I've designed standards converters before (relatively simple 625<>525) I had the tools and techniques readily available.
Steve Anderson wrote:Hmm, where in Australia might you get a 405-line TV? Unless someone unknowingly brought one into the country from the UK in the sixties. NZ had for short while a cable system that ran on 405, but I believe it was short-lived. It's not that easy getting a 405-line TV in the UK, elsewhere I would have thought nigh on impossible.
But given a monochrome 625 TV it's not that hard to 'adjust' the horizontal circuits to suit. The EHT might be the bug-bear though.
One of the small mom & pop corner shops here have a small (around 14") monochrome TV sitting on a shelf in the shop. It's covered in dust and I've never seen it switched on in 16 years. I've made noises that I may be interested in buying it, but to avail. I suspect they're hoarders. Who knows what upstairs looks like! I'm sure it'll need some work to get it going.
I was hoping to use it with the NBTV/SSTV-625 converter thereby negating the colour effects of the shadow-mask CRT on the TV I'm currently using. 14" or so is better suited to SSTV than 21" where you have to stand some distance away from it.
Karen Orton's favorite 5" mono TV's would be even better, but I have never seen one here.
Harry Dalek wrote:As the ic's become more complex this should become easier ? well beyond me but it does interest me i would for sure build one if i could at least i can copy circuits just a bummer the old designs used parts we don't have any more ///Hats off to you very impressive to be able to make one of those !
APRIL FOOL SPOOF 2012
405 line TV in Australia and New Zealand
The Aurora standards converters have been a great success, introducing many people to the joys of 405 line TV. Well over 500 converters have been sold. Not surprisingly the vast majority have been the SCRF405A model, to the UK for running 405 sets. This is followed by the 819 line version for old French sets. Very few other countries used 405 so only a few 405 sets have found their way outside the UK and Ireland. By the time Australia and New Zealand started their TV services 405 was on the way to obsolescence so they started on 625. Despite this a few 405 and dual standard sets have found their way to enthusiasts “down under”. Unfortunately this has exposed a little known problem concerning TV in the antipodes. (I love that word, especially when pronounced “antipoads” by Stanley Unwin) This is the problem of picture inversion.
First a little background. Actually it’s really putting the future before the past because it’s about colour TV. Colour CRTs are extremely sensitive to stray magnetic fields, hence all the shields and degaussing arrangements. The earth’s magnetic field cannot be neglected, with some early sets just changing the set from pointing north/south to east/west could cause visible purity and convergence errors. Moving a set from the northern to the southern hemisphere can also cause visible errors. In older colour sets the purity and convergence were adjusted by the installer so there wasn’t a problem. With later pre-converged CRTs they were available in northern and southern hemisphere versions. Now with flat panel displays there is of course no problem.
In the early days of TV in the antipodes it was found that reversing the vertical scan in both the cameras and receivers could give a noticeable improvement in picture quality. When interchanging programmes between northern and southern countries you got the occasional inversion error but the broadcasters were pretty good at getting it right. Unlike present day widescreen signalling which is frequently done wrong. But what about the poor old 405 line sets that have found their way down under? These were made without inversion facilities and are thus likely to display the picture upside down. The Aurora converter was never designed to cope with this problem. Hardly surprising since there are so few 405 sets in the antipodes. Hence it’s quite likely that these sets will, on occasion, display an inverted picture. The crude answer is a DPDT switch in the feed to the vertical scan coils but this means an unpleasant modification to the set and can often lead to geometry and centring errors as these settings are rarely the same for both polarities. A better solution was needed.
If you are one of that exclusive band of people who have a World Converter (I do wish Darryl had found a better name than WC-01) http://www.tech-retro.com/Aurora_Design ... erter.html there is no problem. A simple firmware upgrade can be done completely free of charge. The SCRF converter is a more difficult problem. It just doesn’t have the hardware resources needed to do the job. After much head scratching Darryl finally found a way to modify the hardware. The new model is called the SCRF405AA (the 2nd “A” is for Antipodean). It is only available to special order and there is a cost premium of $60 (US). It is switchable so that it can still function as a normal SCRF405A. Darryl is also considering a part exchange offer for your existing SCRF405A. This is still being discussed but is likely to be something like $100. Further details of the SCRF405AA can be found here on Darryl’s website: http://www.tech-retro.com/Aurora_Design ... ipode.html
An odd thought occurred to me as I was finishing this note. Many of you will be aware of the role of the Parkes observatory in relaying pictures from Apollo 11. http://www.parkes.atnf.csiro.au/news_events/apollo11/ There were considerable difficulties that have been well explained on that website. One thing they didn’t mention was the inversion problem. It hardly mattered when the pictures were coming from outer space where “up” is not really defined but for pictures coming from the lunar surface they had to make sure they got it right. The world would have thought it strange to see Armstrong and Aldrin wandering about upside down.
I don't know if any of the Antipodean members saw the April Fool spoof that Darryl (the Aurora man) and I ran a few years ago. Here it is for your amusement.
Harry Dalek wrote:HI JeffI don't know if any of the Antipodean members saw the April Fool spoof that Darryl (the Aurora man) and I ran a few years ago. Here it is for your amusement.
NO i had not seen that one ! why do we always get the upside down jokes we are on the positive pole which is up negative is down
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