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Re: History of 29.9



At 03:31 PM 2/13/98 -0500, Craig Fearing wrote:
>The NTSC subcarrier frequency is precisely 3579545 Hz, 

Close enough, but why not pick a subcarrier frequency that was related to
the existing 15.750000Khz,
60.000 monochrome frequency? I was told that the color subcarrier had to be
chosen to be around 3.6MHz- enough below the 4.5Mhz sound intercarrier
subcarrier to be filterable, provide at least 500KHz of double sideband
space for color components and to be an odd multiple of half the nominal
horizontal scan frequency to reduce the visibility of dot patterns created
by the color subcarrier.

The specification for NTSC color subcarrier is 63/88 * 5.00MHz =
3.57954545...MHz
Or (4.5MHz / 286) * (13 * 7 * 5 / 2) = Fsc. (do the factors, they are the
same numbers.)

See Benson, K.B. "Television Engineering Handbook" Revised Edition section
21.3.4 for details.

Thus, the decision was made to screw up the frame rate forevermore to avoid
problems with existing receiver technologies.

Or perhaps I just dreamed that. . .

David Tosh <dlt at earthlink.net>
Engineer, Complete Post Hollywood

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