Re: Apple Graphics Tablet

[Michael J. Mahon <mjmahon@aol.com>]

Alex Freed <alex_news@alexfreed.com> wrote:
> On 6/19/2012 8:37 AM, Michael J. Mahon wrote:
>>  This was a common technique in
>> radar scopes. (And there it's not even being used as a frequency
>> multiplier.)
>> 
> 
> A bit off-topic but IMHO an interesting piece of trivia.
> By the end of the 20th century there was a PLL in every house. Every
> house that had an NTSC (or PAL) TV to regenerate the color sub-carrier
> from just 9 cycles of the "color burst" after line sync. However in the
> early days of NTSC they used a very high Q "LC tank" equivalent - a
> quartz crystal that was excited during the color burst by those 9 periods
> and kept in sync till the next line. Not quite perfect. Probably one of
> the reasons NTSC is claimed by some to stand for Never Twice [the] Same Color. :)
> 
> 
> -Alex.

I don't think that was the earliest design. 

The RCA 630TS, the reference design for the first commercial set, used a
PLL. Of course, based on pulling a crystal oscillator, as were all color TV
sets. 

The "30" in "630" came from the fact that this chassis used 30 tubes to
implement an absolutely textbook NTSC receiver! Later designs took numerous
shortcuts, reducing circuit complexity (and noise tolerance) significantly.
(However, I still don't recall one without *two* PLLs--one for horizontal
sync (and burst gating) and another for color subcarrier recovery.)


-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon