|So why it is 59.94 is beyond me.
The Line Frequency (f line) and Field Frequencies (f field)
for NTSC were defined in the original monochrome systems
with respect to power line frequency. Historically, 525
lines were displayed at a 30 Hz rate (1/2 AC line frequency)
or horizontal line frequency (f line) of 15.75 kHz.
Each TV frequency channel is mandated as 6MHz wide to conserve
the spectrum. The monochrome picture carrier is offset
1.25MHz. The audio carrier is separated from the monochrome
carrier by 4.5MHz (5.75MHz offset). The introduction of
color required a monochrome compatible system while
preventing interference between audio and video carriers
and maintaining a 6MHz bandwidth. To accomplish this and
maintain 4.5Mhz audio, and 525 lines, the line frequency
was changed to an odd multiple of half line rate to ensure:
1) a color burst phase reversal between alternate lines
2) the beat frequency between color subcarrier and average
audio level is approximately 920kHz.
To accomplish this the following definitions were adopted.
a.Line frequency is defined as:
f line = 4.5MHz/286 = 15.73426kHz
b.Field frequency is defined as:
f line/(525/2)= 59.94Hz.
c.Color burst frequency (fsc) is defined as:
fsc = (455/2)*(4.5MHz/286) = 3.579545MHz