This presentation came about due to an after-meeting discussion. We were talking about HDTV, and I was explaining several of the concepts. Someone (Gary Meyer, I think) mentioned that it would make an excellent presentation at one of our meetings.
It was preferable to match the screen refresh rate to the power source to avoid wave interference that would produce rolling bars on the screen. Synchronization of the refresh rate to the power cycle also helped kinescope cameras record early live television broadcasts, as it was very simple to synchronize a film camera to capture one frame of video on each film frame by using the alternating current frequency as a shutter trigger.
The eye is more sensitive to changes in the orange-blue (I) range than in the purple-green range (Q) — therefore less bandwidth is required for Q than for I. Broadcast NTSC limits I to 1.3 MHz and Q to 0.4 MHz. I and Q are frequency interleaved into the 4 MHz Y signal, which keeps the bandwidth of the overall signal down to 4.2 MHz.
NTSC saves only 11% of the original blue and 30% of the red. The green information is usually preserved in the Y channel.
Receivers must sample the incoming signal at very precise intervals to properly interpret the 8-level signal. Improper timing results in receiving useless information, so this makes reception in moving vehicles nearly impossible due to the Doppler effect.