video via powerline - modulating/demodulating video signals - Page 1
Forum section: electronics / beginners

author: ACS
author_rank: Newbie
timestamp: June 10, 2019, 02:05:54 pm
content: I am 14 years old and visit the 9th class at a high school. I look for a diy solution to help my school. The goal of my project is to run a video signal over the powerline. My Idea is to amplitude modulate the analogue video signal with a carrier frequency in the high kHz or low MHz range. Then I will feed that modulated signal over the powerline, on the receiving side I want to filter out the 60hz mains voltages and feed a demodulator with the high frequency modulated signal. What I want is a simple modulator and demodulator, which I can give and receive a (composite) video signal.Can anyone help me by sharing some ideas or circuit’s?Thanks in advance for your assistance!

author: Marco
author_rank: Super Contributor
timestamp: June 10, 2019, 02:13:08 pm
content: Doing powerline data transfer legally is going to be hard. There are existing low frequency signalling protocols you don't want to be interfering with, the higher frequencies might emit EMI.Why not "just" use two raspberri PIs, an USB digitizer and two homeplugs? (Getting it all to work together still won't be entirely trivial.)

author: HB9EVI
author_rank: Frequent Contributor
timestamp: June 10, 2019, 02:55:18 pm
content: Not a very good idea to work on mains directly for a start. I'd maybe support that idea when transmitting a video signal broadband over a coax, but like that? no way.If it's a basic need to get the signal from one room/floor to another, I'd evaluate following points:- is the content to transmit really only available in analog; if the media it origins from is digital, then keep it digital for transmission.- if its origin is digital, use tcp/ip over wifi if there is no wired network; as a hamradio operator I don't encourage you to use powerline communication.- if the content is bare analog, convert it to digital und follow the ideas above.btw. to be more verbose wouldn't be a bad idea. What's the aim of that project? Is it a school project you have to complete or is it a technical problem the school faces for their duties.As a school project, I'd advise you something easier to start with; if it's a school matter, leave the fingers from it - if the school invests on a students agenda and something goes wrong or doesn't work, you're the one to blame - and from my own experience I tell you: that's not the position you want to be in.

author: soldar
author_rank: Super Contributor
timestamp: June 10, 2019, 05:07:45 pm
content: Quote from: ACS on June 10, 2019, 02:05:54 pmYou got that backwards. You modulate the carrier with the signal. The most basic video signal is going to have a bandwidth of 4 - 5 MHz so you will need a carrier at least ten times that. The old lowest VHF channel 2 was 54 MHz. AM modulation of a VHF carrier is not rocket surgery but I do not think it is a beginner's project either. And I am not sure power-line is the best transmission medium. Over the air might go better.You say you are in Germany and you have 60 Hz Mainz?

author: HB9EVI
author_rank: Frequent Contributor
timestamp: June 10, 2019, 06:06:45 pm
content: technically over the air is certainly better, but not by the law. Self built transmitters are reserved to radio amateurs only.Even if there are ISM bands, self constructed devices are not allowed to be operated on those frequencies either.

author: Domagoj T
author_rank: Frequent Contributor
timestamp: June 10, 2019, 06:15:10 pm
content: But why?There are multiple existing solution, both the ones that use mains as the ones that don't. Is the goal to have video transmitted, or is the goal to mess around with mains?

author: HB9EVI
author_rank: Frequent Contributor
timestamp: June 10, 2019, 06:23:49 pm
content: this is why I asked about the nature of this project: is it about learning and constructing a project or just an everydays need which needs mostly a simple and cheap solution...seriously, no sensible teacher would propose a mains project to a 14 year old...and who knows what's true on that first post...

author: ogden
author_rank: Super Contributor
timestamp: June 10, 2019, 07:10:01 pm
content: It is not even worth to consider *analog* video transmission over power lines which are full of noise, especially in time of cheap LED lamps. Design of proper coupler and powerful AC power line *broadband* transmitter alone is complex task. Even if you somehow put your video signal into power line, you will have single channel for whole block behind distribution transformer.In short: AC powerlines are useless means of connecting analog videocamerascamera. You asked for ideas. Here is one: think of other way of helping your school.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 10, 2019, 11:33:31 pm
content: Quote from: ACS on June 10, 2019, 02:05:54 pmYour 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.You can't filter out the Mains frequency signal either, as that would also cause the loss of an important part of the video signalThere are systems that let you do something like this, but they use digital methods.They are also something that cannot be done in a "homebrew" manner, due to both the safety aspect & RF interference possibitiesYou could end up being up to your neck in licencing authorities!

author: ogden
author_rank: Super Contributor
timestamp: June 11, 2019, 08:03:34 am
content: Quote from: vk6zgo on June 10, 2019, 11:33:31 pmNot 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.

author: soldar
author_rank: Super Contributor
timestamp: June 11, 2019, 08:49:41 am
content: Quote from: ogden on June 11, 2019, 08:03:34 amIn 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.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 11, 2019, 11:11:09 am
content: Quote from: ogden on June 11, 2019, 08:03:34 amHe 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.

author: ACS
author_rank: Newbie
timestamp: June 12, 2019, 06:28:21 pm
content: 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?

author: ogden
author_rank: Super Contributor
timestamp: June 12, 2019, 07:22:02 pm
content: Quote from: ACS on June 12, 2019, 06:28:21 pmAnalog 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 schoolQuoteWay 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.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: June 12, 2019, 08:24:34 pm
content: 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.htmlmy guess is they run with a common chip supported by the linux kernel. for a normal old fashioned pal signal it should do