405 NTSC colour
 

There's a possibility that Darryl may reprogram the Aurora standards converter to do 405 NTSC out.

Any interest?

See also:

https://www.vintage-radio.net/forum/...read.php?t=948

Re: 405 NTSC colour
 

Hi Jeffrey

While I am (mightily!) impressed that this can be done. I am **Really** struggling to think of where the feature might be used. :-/ :)

The only possibility that comes to mind is if someone has old broadcast equipment that was used in the early days of colour TV implementation. I seem to remember that NTSC 405 lines were broadcasted experimentally for a time. I believe there was a magazine article on this a while back (405 Alive?).


Chris

Re: 405 NTSC colour
 

There are a small number of the experimental 405 NTSC sets still in existence, but only two or three, I think - can you confirm Jeffrey?

Jim.

Re: 405 NTSC colour
 

David Boynes is restoring one:

http://www.earlytelevision.org/pye_e...tal_color.html

http://www.earlytelevision.org/pye_c...storation.html

Re: 405 NTSC colour
 

Not sure exactly how many of these experimental sets survive but probably fewer than 5.

Re: 405 NTSC colour
 

How many manufacturers do you rekon actually made the odd experimental set ? I assume it was really just the big boys ?

Theres an interesting two-part artical in Wireless World (1956) on the Murphy one.

TTFN,
Jon

Re: 405 NTSC colour
 

I guess it wouldn't be too difficult to modify a dual standard colour set to work on 405 NTSC instead of 625 PAL. Would that make the set more authentic or less? :-/

Retune the bandpass filter and notch filter, fit a new crystal, defeat the PAL switch and shift the chroma phase by 33° - job done! Now where can I get a set?

Re: 405 NTSC colour
 

I don't think you need the 33 degree shift. You can consider NTSC as modulated on the U and V axes. You can modulate and demodulate on those axes. The only thing you lose is the wider I bandwidth. I believe that very few coders or sets actually use the I and Q axes with their different bandwidths.

Re: 405 NTSC colour
 

Yes, of course you're right. Look, it's 12 years since I worked on NTSC... :-[

Re: 405 NTSC colour
 

You may have to add a 'tint' control for the ref osc phase, so you can correct for lilac or puce skin-tones, that NeverTwiceSameColour was renowned for! ;D

David - thought I recognised the name - are you a fellow ex-'Television' scribe?

Re: 405 NTSC colour
 

Good grief, that's going back a bit! My finest hour - the March 1974 issue with my home-built colour set on the cover! 8) Well, I didn't exactly build it from scratch, I used manufacturers' surplus boards where possible. All obtained from the wonderful Manor Supplies. The set cost me nearly £300 if I recall correctly - not much different from buying a set. But the magazine articles paid for the set and left me some pocket money! ;D

Back then there was only one thing to be done with 405 - get rid of it ASAP!

Re: 405 NTSC colour
 

Was that the PTV colour receiver? Or was that a little later?

Re: 405 NTSC colour
 

No, that was nothing to do with me. That was a project to build from scratch. I seem to recall it was done by Keith Cummins. My set used a field timebase/line drive board and the IF strip by Bush (RBM), all solid state. The line output (Pye, valves) and the video board (RBM) were hand built to the manufacturer's circuit and the colour decoder was a design from a large size Mullard paperback book that would probably be worth a lot if I had kept it.

I was working as an apprentice at Marconi in Chelmsford at the time, and a lot of people were building colour sets. We clubbed together to buy the major parts. I well remember a big Mullard truck turning up with I think around 15 to 20 26 " picture tubes.

I recall that the RBM IF strip had an unusual design. It had a quasi-parallel system where one channel did the luminance and the other did the chroma and sound. The theory was that you could have a deep sound notch in the luminance path, which eliminated the bane of early 625 IF's, the wiggly sound/chroma beat pattern. This was of course before the widespread use of synchronous detectors.

To use John (the editor) Reddihough's favourite word, HOWEVER, RBM's design had a fatal flaw that I only sussed years later. They had failed to eliminate the sound/luma beat in the chroma IF. Luma at 1.57MHz would beat with sound at 6MHz to give 4.43MHz. I remember noticing at the time that the cross-colour seemed worse than other sets, but I couldn't think of a reason.