[gugagore]

There are sync pulses on every line of analog video, as well as to color burst in most analog video standards. You couldn't just sweep theta and r continuously for a whole frame.

[Shikadi]

Why not? The sync pulses are because the scan is discontinuous, you could just have one plus color burst every spiral

[gugagore]

I'm guessing that NTSC and PAL have a color burst on every line, vs every frame, because over an entire frame the local oscillator might not be stable enough. At least back in the day.

Same with the timing of the sweep circuits, which only need to hold sync for a single line of video.

[Shikadi]

Oh cool, didn't realize color burst was used for that, I skimmed over it in the past and misunderstood its purpose. TIL