29.97 hz not 30 hz why?

[Don]

Archived from groups: rec.video.desktop (More info?)

I always thought that our ntsc field refresh was 1/60 sec which was
originally tied to our power grid which is 60hz to provide a cheap clock
back when electronics was expensive when tvs were first invented. Now I
see that the frame rates are actually 29.97 hz not 30hz. Does this mean
that the power grid is really at 59.94 hz or are they not really
directly related anymore?

tks

Don

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

> I always thought that our ntsc field refresh was 1/60 sec which was
> originally tied to our power grid which is 60hz to provide a cheap clock
> back when electronics was expensive when tvs were first invented. Now I
> see that the frame rates are actually 29.97 hz not 30hz. Does this mean
> that the power grid is really at 59.94 hz or are they not really
> directly related anymore?

The power grid is still 60 Hz. When NTSC color was introduced, they picked
a close but slightly lower frequency to handle the additional information
without having to take apart the existing standard B&W signal. Owners of
B&W sets, designed to sync to 60 Hz, could watch color transmission (in
B&W, of course) by just making a tiny adjustment to their vertical hold.

--
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[Guest]

Archived from groups: rec.video.desktop (More info?)

Jay Rose CAS wrote:

> The power grid is still 60 Hz. When NTSC color was introduced,
> they picked a close but slightly lower frequency to handle the
> additional information without having to take apart the existing
> standard B&W signal.

There is a fairly good and detailed explanation of all this in here:

<http://google.fi/groups?selm=CHJ9wG.7CH%40fc.hp.com>

--
znark

 

[Guest]

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On a sunny day (Wed, 9 Feb 2005 05:48:15 +0200) it happened "Jukka Aho"
<jukka.aho@iki.fi> wrote in <LJfOd.308$Dl2.88@reader1.news.jippii.net>:

>
>
>Jay Rose CAS wrote:
>
>> The power grid is still 60 Hz.
I have read that during leadin of the latest US 'global' blackout it was down
to 58 for a while, before to went to 0V 0Hz

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

> >Jay Rose CAS wrote:
> >
> >> The power grid is still 60 Hz.
> I have read that during leadin of the latest US 'global' blackout it was down
> to 58 for a while, before to went to 0V 0Hz

You're right. I should have written "The power grid is 60 Hz... when it works."

--
Correct address is spell out the letter j, AT dplaydahtcom
Clio- and Emmy-winning sound design
Learn audio for video at www.dplay.com

 

[Don]

Archived from groups: rec.video.desktop (More info?)

Jukka Aho wrote:
> Jay Rose CAS wrote:
>
>> The power grid is still 60 Hz. When NTSC color was introduced, they
>> picked a close but slightly lower frequency to handle the
>> additional information without having to take apart the existing
>> standard B&W signal.
>
>
> There is a fairly good and detailed explanation of all this in here:
>
> <http://google.fi/groups?selm=CHJ9wG.7CH%40fc.hp.com>
>
this is a super answer to my question. Evidently I didn't manage my
searching very well before,
..tks.

don

 

[Rich]

Archived from groups: rec.video.desktop (More info?)

"don" <nospam@wtez.net> wrote in message
news:36se5tF55mrfpU1@individual.net...
>I always thought that our ntsc field refresh was 1/60 sec which was
>originally tied to our power grid which is 60hz to provide a cheap clock
>back when electronics was expensive when tvs were first invented. Now I
>see that the frame rates are actually 29.97 hz not 30hz. Does this mean
>that the power grid is really at 59.94 hz or are they not really directly
>related anymore?
>
> tks
>
> Don

Not related anymore. When they developed color they added a chrominance
subcarrier which was shifted slight in frequency to avoid interference with
the main video carrier. So it was stuck between two harmonics/ 15,738 Hz
horizontal x 455 Th harmonic divided by 2 = 3.58995 MHz for the chrominance
subcarrier frequency.


Rich