Electronics > Beginners
video via powerline - modulating/demodulating video signals
soldar:
--- Quote from: ogden on June 11, 2019, 08:03:34 am --- Not necessarily. In theory you can put 5MHz channel on 20MHz carrier. Problem here is getting good SNR required for analog video, FCC certification that takes money and no chances with EU certification whatsoever. Conclusion: dead end.
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In theory and in practice you can use that 5 MHz signal to modulate any carrier of any frequency but signal detection can get complicated and there's no point in doing it anyway.
vk6zgo:
--- Quote from: ogden on June 11, 2019, 08:03:34 am ---
--- Quote from: vk6zgo on June 10, 2019, 11:33:31 pm ---Your idea won't work, as the video signal has components from DC to around 5 MHz.
Your "carrier" is within that frequency range, so it will just generate interference signals within the video passband.
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Not necessarily. In theory you can put 5MHz channel on 20MHz carrier. Problem here is getting good SNR required for analog video, FCC certification that takes money and no chances with EU certification whatsoever. Conclusion: dead end.
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He said "high kHz or low MHz" --- 20MHz doesn't really count as "low MHz" in my book!
It was standard practice with analog TV transmitters to perform the modulation at 38.9MHz (Vision carrier) & 33.4 MHz (Sound carrier).
Most of the signal correction, like Group Delay, Differential Gain & Phase, etc, as well as filtering to create a VSB signal was done at this relatively low IF .
The Vision carrier was higher in frequency than the Sound carrier at IF, but that was inverted by the upconverter to channel frequency.
ACS:
Thanks for all of your thoughts and criticism! Obviously, I described the project too superficially. The project is more about creating a proof of concept and learning something along the way. For my tests I always use a low voltage galvanically isolated 50hz/60hz sinewave, generated by an audio amplifier for safety. My first idea was to use a fully analogue system, because of its relative simplicity and latency. But I see your points concerning interferences and bandwidth problems. So, in the future I plan to go the digital way, as recommended from many of you. I plan to use a premade “ethernet over powerline adapter”, two Raspberry Pi’s and an USB digitizer. I hope that, I will have more success that way.
Thanks again to all of you, for taking the time to correct my ideas or provide new ones.
postscript: After a quick Internet research, it seems to me that USB digitiser are pretty expensive. Is there any way to built one myself, maybe with a universal Atmel microcontroller (With an SPI output? Or are there two slow?)? Or are there more operational specific IC´s for that purpose?
ogden:
--- Quote from: ACS on June 12, 2019, 06:28:21 pm ---postscript: After a quick Internet research, it seems to me that USB digitiser are pretty expensive.
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Analog video is outdated technology- that's why. Today you shall be looking for Ethernet-enabled video cameras with H.264 compression. You plug such camera into ethernet over powerline adapter and that's it - you helped your school
--- Quote ---Is there any way to built one myself, maybe with a universal Atmel microcontroller (With an SPI output? Or are there two slow?)
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Way too slow. Atmel AVR with 8Kbytes RAM you can have 64*48 pixels frame buffer. ADC speed is even worse. You can sample maximum 4 horizontal pixels of each video line using AVR.
HB9EVI:
that's quite reasonable; maybe try with those ones:
https://de.aliexpress.com/item/Kebidumei-USB-Video-Capture-Ger-t-USB-2-0-Einfach-zu-Cap-Video-TV-DVD-VHS/32948322499.html
my guess is they run with a common chip supported by the linux kernel. for a normal old fashioned pal signal it should do
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