Service manual

STP 11-25R13-SM-TG
S - 23
(7) This frequency is within the deviation limit set by the NTSC monochrome standards. With the
horizontal scan frequency changed, the color subcarrier must be chosen to interleave. It must be an odd
multiple of one-half the horizontal-scan rate. With 3.6 MHz as an upper limit, it was found that the 455th
harmonic of half the horizontal scan rate becomes:
F (color subcarrier) = 455 x
15,734.26 Hz
= 3.579545 MHz
2
(8) Since there are 525 lines and using a 2:1 interlace, the new vertical scan frequency becomes:
F (Vertical) =
2
x
15,734.26 Hz
= 59.94 Hz
525 1
(9) Note that the new scanning frequencies used for color transmission are slightly below the
nominal values used in monochrome receivers. However, the changes amount to less than the
percentage allowed and the new frequencies fulfill the requirements for compatibility in monochrome
reception.
(10) To maintain close synchronization of color receivers, the tolerance for the subcarrier frequency
is set at +0.0003 percent, or around +10 Hz; the rate of change cannot be more than 1/10th Hz per
second. The same tolerance applies to the field and line frequencies. In actual practice, all of these
frequencies are developed from the same source to minimize variations from the established figures.
S-21. Bandwidth Limitations.
Since picture detail is a function of the transmitted signal bandwidth, and since there is a limited
amount of bandwidth allowed for chrominance information, this is an important point to consider. As
shown in Figure S-22, the highest usable video brightness signal frequency is 4.1 MHz, with the
chrominance subcarrier at 3.58 MHz.
Figure S-22. R-Y and B-Y Chromaticity Coordinates