On Friday, 23 June 2017 18:41:14 UTC+1, NY wrote:
tabbypurr wrote in message
...
625 line PAL VCRs recorded 405 line material happily enough. They didn't
give a damn what was in the signal as long as the frame pulses were the
right time apart.

Yes, I've heard this. The only thing that matters is the spacing of the
frame sync pulses; the number of line sync pulses (i number of lines)
doesn't matter.

The difficulty is getting access to a 405-line signal. The tuner in all UK
VHS recorders was UHF/625-line only, so you'd need a VHF/405-line tuner that
could output baseband video

no-one broadcasts 405 so not much point. It was similarly pointless pre-82 for different reasons.

and a modulator to convert the off-tape signal
back to a form that the TV could play. And you'd need to do it before
broadcasters stopped broadcasting 405-line in the mid 1980s.

Easier to inject the baseband signal into the tv after the tuner. That's what I did, not a live chassis set. If it is I won't mumble anything about neutrals & RCDs.

Nowadays there are a few hobbyists who have developed modified PCs which
produce standards-compliant 405/25 video by driving the graphics card in a
special mode, and so they could play any video file (off-air MPEG, Youtube).
You could even convert from DVB-T2 1920x1080 high-definition to 405-line!

As you say, that 450-line signal could be recorded and played back on VHS.

Then you need a modulator or else a modified TV which allows you to inject
baseband video.

no mod needed on mine. I don't know if tuner output levels & polarity were standardised though.

As an aside, I wonder what your average 625/25 telly would make of a 405/25
signal (assuming you got past the different modulators and fed baseband).

total scramble. I tried getting a B&W to slow down to 405 and it just would not pull down far enough no matter what I did. If you look at old 405/625 dual standard sets they had massive slide switches to switch a long list of circuit operations.

The frame would sync perfectly but the lines would be all scrambled. Is 625
divided by 405 a simple enough relationship that you'd see a static pattern
of lines, I wonder?

ISTR that with the right line speed adjustment I got an image that was clearly mathematically related and lined up every several lines. So I could see roughly what was on the reording, but it wasn't watchable.

30 line TV is fun too - very different.


NT

It always amazed me that modern European tellies and VCRs can usually copy
with NTSC tapes and signals: I have played a US VHS tape in my player and
got a stable picture (reduced height, corrupted colour due to alternate
lines not having the required phase reversal) - usually accompanied by a
loud clonk as a relay in my telly switches in a different frame-sync
circuit.

The converse is not true: much less US kit can play PAL tapes and signals -
presumably because of The World Ends At The US Borders syndrome :-)