OT: discussion on TV frequency history, was RE: [MPlayer-users] R e: which deinterlace filter

[D Richard Felker III]

On Tue, Oct 21, 2003 at 10:56:46PM +0200, Karl Ewald wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> Hi Rich,
> 
> I must say Reimar's comments do sound sensible to me.
> While in digital circuitry, it is easy to divide frequency by using a
> counter, this cannot be done in the same way in analog circuitry. So instead

Frequency divider is trivial. We were talking about frequency
multiplier = time divider, and I have no idea how you do that without
having a higher frequency clock source to begin with...

> you will happily use different sources for the horizontal and the vertical
> timebase, since it doesn't really matter how the vertical rescan relates to
> the horizontal position, you have a fairly large number of horizontal lines
> that are blanked out between successive pictures, during which you need to
> move the electron beam back up vertically, it doesn't really matter how this
> is aligned with the horizontal oscillation.
> 
> I wouldn't be surprised if you had in fact trouble hooking up a VCR even to
> a 60s made TV set, and the vertical frequency generator issues discussed are
> stemming from the 40s or early 50s!
> 
> I recall reading in an operating manual for a 1975 made PAL color TV set
> (WEGA brand, if anyone cares, built from a mix of tubes and transistors)
> that program button 8 (the highest one) is intended for attaching a VCR or
> video player and has a shorter timebase (can't remember the exact term, and
> I'm translating it to English now anyway, so please don't be too picky about
> the expression), so apparently it was known that the video signal modulated
> (there was no video-in, so the attached device had to have an HF modulator
> in it to merge the signal as an additional channel onto the antenna cable)
> from video playing devices was slightly different from the one received from
> live broadcast.
> 
> I recall that we had late 50s or 60s made b&w TV sets which had adjustment
> knobs called "catch" (German: Fang) which as I recall were used to fine-tune
> the frequency generators to the broadcast signal to avoid the picture from
> "running through" (or, indeed force it to by misadjusting). This would
> indicate that in these TVs, the vertical frequency was not taken from the
> power supply, at least not directly, since this wouldn't have allowed
> adjusting it in any way. But that was already at least a decade or two after
> the invention of TV broadcast so the first devices may well have done it
> that way.
> It also indicates that back then it was certainly not easy to "lock onto"
> sync signals without already having a timebase that is very close to that of
> the signal, that's why your idea "the actual sync pulses can drive the
> refresh" doesn't suffice without having already a suitable frequency
> generator to match them.
> 
> Karl

Thanks for the info, though I'm still skeptical regarding the
relationship of all this to whether color TV signals could be watched
on early B&W TVs. BTW, please don't top-quote on mailing lists. Many
people consider it impolite.

Rich