Hacker News Reader

Comment by mjevans | Hacker News Reader

Analog circuits aren't my area of expertise. However it seems likely that the complexity of a stable and identical spiral scan circuit is either extremely difficult or possibly improbably expensive.

Compare the above to what we have in reality: it seems that there were some vacuum tube tricks that made a grid system much easier. https://en.wikipedia.org/wiki/NTSC#Technical_details

View on HN

A spiral scan circuit would just be something like:

x = r cos (theta) y = r sin (theta)

when you vary r so it gives you a spiral instead of a circle. So it shouldn't be too hard to generate the signals required.

Or there could be a different arrangement of the beam deflectors that didn't give you independent control of X and y.

But getting equal time on each pixel as you spiral out would be crucial to trigger the right phosphorescent equal luminance from your light-emitting material. Theta would not be linear with time.

The intensity of the beam could be modulated to counter this.

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.

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

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.

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

Reply on news.ycombinator.com