A DC synchronization aka "sync" pluse was included to
keep everything together so if signal got scrambled, the TV
would bring it back together quickly.

Actually, the sync pulses keep the horizontal and vertical scanning in the
receiver at the same frequency and phase as the transmitted signal.


Those rates were chosen because the studio lights were arc
lights and flashed on and off at the power line rate, so the TV
cameras had to be syncronized to them or you would get moving
black stripes across the screen.

This might have been a consideration, but the principal concern was "hum
bars" in the receiver. Modern power supplies are sufficiently well-filtered
that this isn't a concern.


The RCA system for compatible color TV (compatible with black
and white), used 1/4 of the color information based on the fact
that your eye only sees about that much.

Actually, it's more like 1/3.


The color information was encoded on a phase modulated 3.57MHz
subcarrier, which at the time was beyond the picture information, but
still within the transmitted signal.

Actually, it was within the picture (luminance) information. NTSC has always
had a potential video bandwidth of 4.2 MHz.


The original RCA system, alternated the phase of the carrier every line,
so that it would fix itself if there was a transmssion or syncrhonization
problem. To save money, the National Television Standards Commitee
(NTSC) which chose the standard, dropped the alternating phase.

Actually, it was dropped because it didn't seem possible at the time to
design a reasonably priced receiver that would take full advantage of this
feature (in particular, the elimnation of the Hue control). Also, the US
distribution system didn't have problems with non-linear phase, so PAL had
little practical advantage.

Also, the original proposal used red and blue color-difference signals,
rather than the more-efficient I and Q. The original NTSC proposal was
virtually identical to PAL. (If you don't believe this, I have a copy of
"Electronics" magazine that confirms it.)


The French used a different color encoding system called SECAM,
which was also based on the RCA system (1/4 color, 4.43mHz color
carrier) but designed to be totally incompatible so that you could not
watch French TV in England and vice versa.

SECAM stands for "sequential avec memoire".

SECAM was actually adopted because the French were idiots. They wanted a
system that was relatively easy to record on videotape. Unfortunately, it
made the receiver more-complex and expensive. A classic example of lousy
engineering.