PDP-8 and other rare mini computers
http://www.pdp8.com
-----Original Message-----
From: Eric Smith <eric_at_brouhaha.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Thursday, December 09, 1999 7:35 PM
Subject: NTSC sync rate (was Re: Hewlett Packard A2094 Monitor (Standard
RGB?))
>"John B" <dylanb_at_sympatico.ca> wrote:
>Tony wrote:
>> US TV is 15.570kHz, VGA is 31.25kHz or thereabouts.
>
>John B wrote:
>> No, the US TV (NTSC) Scan Rate is 15.750Khz
>
>Well, if you want to get nitpicky, the NTSC horizontal sync
>rate is 15.73425 KHz.
I know.. I didn't want to get *picky*.. the vertical rate is 59.94...
>
>The old EIA RS-170 monochrome standard was 15.750 KHz, but that
>is not suitable for NTSC color use. The color burst frequency
>is 3.579545 MHz +/- 10 Hz, and the the horizontal rate is required
>to be exactly 2/455 of that frequency. Otherwise the color information
>will produce luma artifacts and/or interfere with the sound carrier.
>
>Note that they could have chosen to make the color carrier 3.583125 MHz,
>and kept all the video timing exactly the same as for RS-170. Then they
>would have had to raise the center frequency of the audio carrier by
>0.1%. The FCC apparently would not let them make that change, in the
>interest of compatability with existing monochrome receivers (which is
>incredibly stupid, since the receivers wouldn't have even noticed), so
>they had to lower everything else by 0.1% instead. Thus the need for
>disgusting hacks like drop-frame time code. Sigh.
>
>Eric
>
>
>Reference: _A Technical Introduction to Digital Video_ by Charles A.
>Poynton, John Wiley & Sons, 1996
>
Received on Thu Dec 09 1999 - 17:40:48 GMT