From: VWWall 
Newsgroups: alt.engineering.electrical
Subject: Re: 240 volts
Date: Wed, 05 Mar 2008 12:44:10 -0800
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Dave Martindale wrote:

> For the record, here is something I wrote (a long time ago) to explain where
> the magic numbers in NTSC come from.  The ratio 63/88 does not appear
> anywhere in the original standard that I could see.  There are a number of
> other ratios that do appear, and a particular product of them can be reduced
> to 63/88.  So that value is theoretically exact - but knowing it doesn't tell
> you anything about where it came from.  The note below does.



I was a junior engineer at Bell Labs at about the time all this was 
happening, but not directly involved with TV.  Thanks for the insight!

Aren't we glad that the CBS method of using a whirling "color wheel", 
didn't become the standard.  I actually built a working model in 1949. 
The DLP TV sets have gone back to this way of getting color!

It would be interesting to attempt to do your analysis on PAL or SECAM, 
(or even the new digital standards).

-- 
Virg Wall, P.E.

From: [email protected] (Dave Martindale)
Newsgroups: alt.engineering.electrical
Subject: Re: 240 volts
Date: Thu, 6 Mar 2008 20:59:51 +0000 (UTC)
Organization: University of British Columbia, Canada
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VWWall  writes:

>I was a junior engineer at Bell Labs at about the time all this was 
>happening, but not directly involved with TV.  Thanks for the insight!

Thanks.

>It would be interesting to attempt to do your analysis on PAL or SECAM, 
>(or even the new digital standards).

I'd be interested as well, but it would probably have to be done by
someone with better access to PAL or SECAM documentation.  I just happen
to have a copy of the NTSC committee's original report, but nothing
similar for the other standards.

What I do know:

PAL started from a monochrome system with different frame and field
rates, wider channel spacing, and thus more video bandwidth.  This
allowed them to use a higher subcarrier frequency, reducing its
visibility.  Despite that, there was room in the channel to transmit
both colour components double sideband, so they could encode (R-Y) and
(B-Y) directly instead of having to generate I and Q.

But they did a couple of weird things.  They specified different RGB
colour primaries (which are probably more realistic than the NTSC ones).
But instead of recalculating the RGB to YUV transform matrix for these
new primaries, they re-used exactly the same matrix as NTSC.  And the
relationship between subcarrier and H sync is more complex, with a 90
degree phase shift per frame that I don't understand at all.

	Dave


From: [email protected] (Michael Moroney)
Newsgroups: alt.engineering.electrical
Subject: Re: 240 volts
Date: Wed, 5 Mar 2008 22:01:09 +0000 (UTC)
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[email protected] (Dave Martindale) writes:

>For the record, here is something I wrote (a long time ago) to explain where
>the magic numbers in NTSC come from.  The ratio 63/88 does not appear
>anywhere in the original standard that I could see.  There are a number of
>other ratios that do appear, and a particular product of them can be reduced
>to 63/88.  So that value is theoretically exact - but knowing it doesn't tell
>you anything about where it came from.  The note below does.

[snip]

Fascinating.  That also explains the mystery why the vertical synch was
defined to be 59.94 Hz when it "should have been" 60 Hz to avoid power
line interference effects.

From: [email protected]
Newsgroups: alt.engineering.electrical
Subject: Re: 240 volts
Date: 6 Mar 2008 02:24:59 GMT
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On Wed, 5 Mar 2008 22:01:09 +0000 (UTC) Michael Moroney  wrote:
| [email protected] (Dave Martindale) writes:
| 
|>For the record, here is something I wrote (a long time ago) to explain where
|>the magic numbers in NTSC come from.  The ratio 63/88 does not appear
|>anywhere in the original standard that I could see.  There are a number of
|>other ratios that do appear, and a particular product of them can be reduced
|>to 63/88.  So that value is theoretically exact - but knowing it doesn't tell
|>you anything about where it came from.  The note below does.
| 
| [snip]
| 
| Fascinating.  That also explains the mystery why the vertical synch was
| defined to be 59.94 Hz when it "should have been" 60 Hz to avoid power
| line interference effects.

And it's a good thing they did design it the way they did.  Otherwise the
backronym for NTSC would have become (N)o (T)elevision (S)ince (C)olor.

-- 
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org)  /  Do not send to the address below |
| first name lower case at ipal.net   /  [email protected] |
|------------------------------------/-------------------------------------|

From: [email protected] (Dave Martindale)
Newsgroups: alt.engineering.electrical
Subject: Re: 240 volts
Date: Thu, 6 Mar 2008 21:18:42 +0000 (UTC)
Organization: University of British Columbia, Canada
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[email protected] (Michael Moroney) writes:

>Fascinating.  That also explains the mystery why the vertical synch was
>defined to be 59.94 Hz when it "should have been" 60 Hz to avoid power
>line interference effects.

It actually was 60 Hz in B&W days.

In retrospect, it seems like changing all of the video frequencies to
avoid touching sound was a bad decision.  If they'd just left sound
alone, it wouldn't be quite an odd multiple of half the line frequency,
but it's FM anyway - it's not a fixed frequency.  Or they could have
move the sound carrier up a bit - a 4500 Hz shift in sound frequency
in a system with 25 kHz deviation should not have screwed up sound
receiption in the old B&W TV sets.

Either way, we could have had exactly 60 Hz frame rate, and drop-frame
time code would never have been invented, and the slow time error
accumulation of even drop-frame code would not worry anyone.  And 24 FPS
films could be run at exactly 24 FPS instead of 23.98.  Many potential
headaches would disappear.

On the other hand, ironically, the multiplier to generate subcarrier
from a 5 MHz reference source would become 5733/8000 instead of the
value of 63/88 we have now.  By pure blind luck, the 1000/1001
multiplier used to shift the video frequencies just happens to cancel
most of the prime factors of 455:

	455/1001 = (5*7*13)/(7*11*13) = 5/11

and that's mostly why you get the simpler 63/88.

	Dave

From: [email protected]
Newsgroups: alt.engineering.electrical
Subject: Re: 240 volts
Date: 7 Mar 2008 02:25:30 GMT
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On Thu, 6 Mar 2008 21:18:42 +0000 (UTC) Dave Martindale  wrote:
| [email protected] (Michael Moroney) writes:
| 
|>Fascinating.  That also explains the mystery why the vertical synch was
|>defined to be 59.94 Hz when it "should have been" 60 Hz to avoid power
|>line interference effects.
| 
| It actually was 60 Hz in B&W days.
| 
| In retrospect, it seems like changing all of the video frequencies to
| avoid touching sound was a bad decision.  If they'd just left sound
| alone, it wouldn't be quite an odd multiple of half the line frequency,
| but it's FM anyway - it's not a fixed frequency.  Or they could have
| move the sound carrier up a bit - a 4500 Hz shift in sound frequency
| in a system with 25 kHz deviation should not have screwed up sound
| receiption in the old B&W TV sets.
| 
| Either way, we could have had exactly 60 Hz frame rate, and drop-frame
| time code would never have been invented, and the slow time error
| accumulation of even drop-frame code would not worry anyone.  And 24 FPS
| films could be run at exactly 24 FPS instead of 23.98.  Many potential
| headaches would disappear.

ATSC has real 60 Hz (and 30 Hz and 24 Hz) as optional modes, in addition
to those that are 1000/1001 lower.


| On the other hand, ironically, the multiplier to generate subcarrier
| from a 5 MHz reference source would become 5733/8000 instead of the
| value of 63/88 we have now.  By pure blind luck, the 1000/1001
| multiplier used to shift the video frequencies just happens to cancel
| most of the prime factors of 455:
| 
|        455/1001 = (5*7*13)/(7*11*13) = 5/11
| 
| and that's mostly why you get the simpler 63/88.

A fixed number of audio samples per field would be nice, too.  That is not
the case with 59.94 Hz and either 44100 Hz or 48000 Hz.  With 44100 Hz, we
get exactly 735.735 audio samples per field (see how 1001 affects that).
With 48000 Hz we get exactly 800.8 audio samples per field (see how 1001
also affects that, too.  If we had exactly 60 Hz, we would have exactly
735 or 800 samples per field.  OTOH, exactly 120000 Hz as an audio sample
rate will give a whole number of audio samples per field for all field
rates (5005 at 23.976 fps, 5000 at 24 fps, 4800 at 25 fps, 4004 at 29.97
fps, 4000 at 30 fps, 2400 at 50 fps, 2002 at 59.94 fps, 2000 at 60 fps, as
well as 1001 at 119.88 fps and 1000 at 120 fps for those shooting video in
those special high frame rate cameras).

-- 
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org)  /  Do not send to the address below |
| first name lower case at ipal.net   /  [email protected] |
|------------------------------------/-------------------------------------|

From: "Michael A. Terrell" 
Newsgroups: alt.engineering.electrical
Subject: Re: 240 volts
Date: Thu, 06 Mar 2008 21:42:34 -0500
Organization: http://home.earthlink.net/~mike.terrell/
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Dave Martindale wrote:
> 
> [email protected] (Michael Moroney) writes:
> 
> >Fascinating.  That also explains the mystery why the vertical synch was
> >defined to be 59.94 Hz when it "should have been" 60 Hz to avoid power
> >line interference effects.
> 
> It actually was 60 Hz in B&W days.
> 
> In retrospect, it seems like changing all of the video frequencies to
> avoid touching sound was a bad decision.  If they'd just left sound
> alone, it wouldn't be quite an odd multiple of half the line frequency,
> but it's FM anyway - it's not a fixed frequency.  Or they could have
> move the sound carrier up a bit - a 4500 Hz shift in sound frequency
> in a system with 25 kHz deviation should not have screwed up sound
> receiption in the old B&W TV sets.
> 
> Either way, we could have had exactly 60 Hz frame rate, and drop-frame
> time code would never have been invented, and the slow time error
> accumulation of even drop-frame code would not worry anyone.  And 24 FPS
> films could be run at exactly 24 FPS instead of 23.98.  Many potential
> headaches would disappear.


   Headaches? No.  Minor problems, at best.  You have to realize how
primitive electronics was when NTSC was developed.  Or they could have
just kept TV monochrome, until digital technology was perfected. The
development of NTSC video mandated compatibility with existing
monochrome TV sets, and introducing a sync buzz wasn't acceptable. 
There was also a problem with chroma noise crawling up the screen if
they kept the original timing.

 
> On the other hand, ironically, the multiplier to generate subcarrier
> from a 5 MHz reference source would become 5733/8000 instead of the
> value of 63/88 we have now.  By pure blind luck, the 1000/1001
> multiplier used to shift the video frequencies just happens to cancel
> most of the prime factors of 455:
> 
>         455/1001 = (5*7*13)/(7*11*13) = 5/11
> 
> and that's mostly why you get the simpler 63/88.


   Considering that frequency division was done with vacuum tube
multi-vibrators, they had to keep the ratios as simple as possible.  We
are talking tubes like the 6SN7, octal based tubes.  There were no fancy
phase locked loop synthesizers back then. 


> 
>         Dave


-- 
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

From: [email protected]
Newsgroups: alt.engineering.electrical
Subject: Re: 240 volts
Date: 7 Mar 2008 03:34:42 GMT
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On Thu, 06 Mar 2008 21:42:34 -0500 Michael A. Terrell  wrote:

|   Considering that frequency division was done with vacuum tube
| multi-vibrators, they had to keep the ratios as simple as possible.  We
| are talking tubes like the 6SN7, octal based tubes.  There were no fancy
| phase locked loop synthesizers back then. 

OTOH, 63/88 would not have been hard to do, given the range of frequencies.

I don't know if they knew of this method, or not.  But they most certainly
did know the pre-requisites, which were to generate harmonics, filter a
narrow band, do phase comparison, and work at UHF frequencies.  What could
be done is take the 63rd harmonic of 5 MHz (or 21st harmonic of 15 Mhz if
that would be easier), and take the 88th harmonic of 3.579545 MHz (or the
22nd harmonic of 14.318182 MHz if they wanted that), bandpass filter them
at 315 MHz, and do the phase comparison there.  Then the phase error would
be used to tweak the derived frequency oscillator.

An actual circuit design using tubes of the era is left as an exercise for
the readers that really care.

-- 
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org)  /  Do not send to the address below |
| first name lower case at ipal.net   /  [email protected] |
|------------------------------------/-------------------------------------|