General > General Technical Chat
Why does NTSC use a strange frequency for the chroma carrier?
BrianHG:
This is what it looks like if your video frame rate doesn't match you AC's source line frequency and there is some magnetic flux leakage into your picture tube via magnetic or electrical drive:
(Seek to 3:33.)
If the MCU outputted that logo at a perfect 60hz refresh cycle speed, even through there may be a slight warping in that image, the warp pattern would have been static still and not visible.
Ben321:
Now days we have solid state drive circuits for CRTs that can much better produce the precise horizontal and vertical scanning frequencies. For example, VGA CRT computer monitors could easily be driven at 75Hz or 85Hz vertical scanning rate for more flicker reduction (the faster the vertical scan rate, the less the picture appears to flicker to the human eye).
BrianHG:
--- Quote from: Ben321 on January 16, 2023, 12:25:26 pm ---Now days we have solid state drive circuits for CRTs that can much better produce the precise horizontal and vertical scanning frequencies. For example, VGA CRT computer monitors could easily be driven at 75Hz or 85Hz vertical scanning rate for more flicker reduction (the faster the vertical scan rate, the less the picture appears to flicker to the human eye).
--- End quote ---
Yes, but even with a top of the line studio multiscan CRT, here in North-America, at 75hz, in some locations we can see the image wobble 15 times a second due to high power tension lines being within a block of your location. It doesn't matter how good the CRT electronics are if you are bathed in a 60hz magnetic field like I am during the coldest winter days and hottest summer days where the high tension power lines 2 blocks from my how radiate such a strong field, I can measure AC voltage on disconnected transformer cores, large ones giving enough to light a LED. The next non-wobbly vertical scan rates step up is 90hz or 120hz video.
james_s:
--- Quote from: BrianHG on January 16, 2023, 01:30:55 pm ---Yes, but even with a top of the line studio multiscan CRT, here in North-America, at 75hz, in some locations we can see the image wobble 15 times a second due to high power tension lines being within a block of your location. It doesn't matter how good the CRT electronics are if you are bathed in a 60hz magnetic field like I am during the coldest winter days and hottest summer days where the high tension power lines 2 blocks from my how radiate such a strong field, I can measure AC voltage on disconnected transformer cores, large ones giving enough to light a LED. The next non-wobbly vertical scan rates step up is 90hz or 120hz video.
--- End quote ---
I've seen houses that are directly under or very near high tension transmission lines. I always thought it would be interesting to put a large coil in the attic and see how much power could be extracted from that.
BrianHG:
--- Quote from: james_s on January 16, 2023, 08:37:17 pm ---
--- Quote from: BrianHG on January 16, 2023, 01:30:55 pm ---Yes, but even with a top of the line studio multiscan CRT, here in North-America, at 75hz, in some locations we can see the image wobble 15 times a second due to high power tension lines being within a block of your location. It doesn't matter how good the CRT electronics are if you are bathed in a 60hz magnetic field like I am during the coldest winter days and hottest summer days where the high tension power lines 2 blocks from my how radiate such a strong field, I can measure AC voltage on disconnected transformer cores, large ones giving enough to light a LED. The next non-wobbly vertical scan rates step up is 90hz or 120hz video.
--- End quote ---
I've seen houses that are directly under or very near high tension transmission lines. I always thought it would be interesting to put a large coil in the attic and see how much power could be extracted from that.
--- End quote ---
Like these: https://shop64002.carrierwrt.org/category?name=fluorescent%20light%20under%20power%20lines
Yes, most if not all of those are real.
Thanks to a 25 foot metal beam which was the edge of my workbench desk at my house, if I placed 1 electrode into the ground and one on that desk beam as an antenna, I got around 1watt of free power.
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