[BC] TV question

[PeterH]

On Feb 6, 2010, at 8:36 AM, Ron Youvan wrote:

> The last time this came up I looked at several old DVD players and  
> the vertical
> interval WAS 59.94 Hz and NOT 60 Hz.

The Vertical Drive frequency is 59.94 Hz, and it has been since NTSC  
was standardized.

The frame rate is 29.97 Hz.

In the old days, the reference was a 31,500 Hz crystal. 31,500 Hz was  
the Equalizing Pulse frequency. The Horizontal Drive frequency was  
one-half of that, or 15,750 Hz.

With the coming of NTSC, all references are taken from the 3.579545  
MHz color burst frequency, which is actually maintained as a 14.31818  
MHz crystal oscillator.

The Equalizing Pule frequency is one-quarter of 14.31818 MHz, or  
31368.53 KHz. The Horizontal Drive frequency is one-half that, or  
15734.26 Hz. The frame rate is one-five-hundred-twenty-fifth of that,  
or 29.97 Hz.

As several frequencies and rates are related by 2-to-1, a super- 
multiple of the color burst frequency must be the starting point.  
14.31818 MHz is the most convenient reference for this purpose.