alt Hacker NewsSECAM was pretty crazy because it required a delay line: a memory that would hold the previous scanline so it can be combined with the current one.
Without digital circuits, the delay line was a piece of glass. You’d convert the video signal to a sound wave, send it through the glass, and (hopefully) get it back exactly 64 us later so it aligns with the next scanline.
Here’s a picture: https://www.eevblog.com/forum/projects/glass-ultrasonic-dela...
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lbourdages • yesterday at 5:19 PM
Fascinating! So it's a bit like a plate reverb (used in the olden days in audio engineering), but in the MHz range.
Yes I did read about these while doing my research. Also fascinating. Most (or maybe all?) PAL TVs also have a delay line to correct for phase errors. That ability is what differentiates PAL from NTSC, apart from timing.