Crosley 9-413B Horizontal Issue

[Penthode]

Originally Posted by Penthode

The horizontal frequency is actually 15,734.26573426573 Hz. Or rounded off 15.73 kHz

To calculate the horizontal frequency:

4,500,000 ÷ 15,750 = 285.7142857142857

Round up to 286:

4,500,000 ÷ 286 = 15,734.2657....

The reason? When over 70 years ago NTSC color was being formulated, to minimize a beat interference between the FM sound carrier at 4,500,000 Hz and the color subcarrier nominally at 3.58MHz, the original horizontal sweep frequency was shifted slightly to ensure the sound carrier was an exact integer multiple of the horizontal frequency. The sound carrier could have shifted instead but the concern was that the millions of intercarrier sound TVs would require minor realignment.

The color subcarrier therefore will be 455 times half the new horizontal frequency to minimize beating with the sound carrier:

15,734.265734426573 ÷ 2 X 455 = 3,579,545.454545455 Hz

[old_tv_nut]

Stated as a rational number rather than a repeating decimal, the color subcarrier frequency is
3579545 + 5/11 Hz
5/11 = 0.45454545...

This comes about because of the prime factors of 455. 455 was chosen instead of some close possible numbers because it is the product of some fairly small prime numbers. Each counter stage dividing by a fairly small number meant that the tube frequency dividers of the time were less likely to drift out of tolerance enough to cause a wrong count.