Transmit video/instructions to old TV ? - Page 1
Forum section: electronics / rf-microwave

author: lordvader88
author_rank: Frequent Contributor
timestamp: February 22, 2019, 02:59:27 pm
content: I want to get a really really old TV, with tubes, or just transistors, no IC's, could be B/W. Just to play with and learn from, like old radio's I have. I think there's still analog TV stations here. But if not, I see tons of DIY AM/FM audio transmitter circuits, what about DIY video transmission circuits ?What about just sending something basic, like turn the screen 1 color, then another. Just across the room. If they could do it in the 1930s, I hoping it's not that much more complicated than the 1,000s of basic radio circuits online.Just wondering, for someday, when I get a vintage TV

author: CJay
author_rank: Super Contributor
timestamp: February 22, 2019, 03:25:17 pm
content: Find a modulator from an old 8 bit computer and attach an antenna?You'll need to feed it an analogue video signal of course and generating that is going to be the most difficult part, if you can find somehting like a MC1377 (not too difficult) and the necessary delay line (difficult) it would make it much simpler.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 22, 2019, 03:44:30 pm
content: You are very late to the game. There used to be millions of little channel 3/4 modulators that would take the composite NTSC video signal and modulate it onto one of the old VHF channels (now illegal).While the MC1377 is great for creating the composite signal, you still have to modulate it onto an old TV channel to get it into the antenna connection. Unless you find a TV with a video input (good luck with that).Amazing enough you can still buy a modulator at BestBuy:https://www.bestbuy.com/site/insignia-rf-modulator-black/4947028.p?skuId=4947028Or else find an old discarded VHS cassette machine and recycle the little modulator module out of it.

author: lordvader88
author_rank: Frequent Contributor
timestamp: February 22, 2019, 04:59:26 pm
content: I need some old TV books to study, thats way ahead of the tech I was hoping for.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 22, 2019, 05:10:54 pm
content: Quote from: lordvader88 on February 22, 2019, 04:59:26 pmI'm not quite sure what you are trying to learn here?Old OTA (Over The Air) television on VHS and then UHF was simply AM modulation for the luminance (black and white) channel. Then when they added color, they created a sub-channel at 3.579545 MHz up from the base-band channel frequency. That left the base-band luminance channel essentially unchanged for backwards-compatibility with B&W television receivers.Transmitting video over the air was simply AM modulating the luminance+sync exactly like AM radio except a different signal (video instead of audio) and on a different frequency (MHz for television vs. KHz for AM radio)There is all manner of information about the origins and history and technology of television available on Wikipedia. You could start with the article on NTSC.https://en.wikipedia.org/wiki/NTSCEDIT: If you were hoping to actually transmit television through the air (vs. a direct connection to the antenna input) you should know that it is probably even more illegal now than it was back when VHS analog was in wide use. The US and Canada have kicked old analog TV out of the old VHF band and most of the UHF band as well.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 22, 2019, 05:20:03 pm
content: We don't know were you are in Canada, so maybe there are "still analog TV stations here" depending on where "here" is? The history of transition from analog to digital terrestrial television broadcasting in Canada appears to be a mishmash of changing decisions. Even worse than here in the US. You can read the sordid details here:https://en.wikipedia.org/wiki/Digital_terrestrial_television_in_Canada#Transition_detailsIn any case you better hurry. because the last decision is that analog TV in Canada will be shut down in 2022

author: CJay
author_rank: Super Contributor
timestamp: February 22, 2019, 08:10:14 pm
content: Quote from: Richard Crowley on February 22, 2019, 03:44:30 pmThat was kind of my point, creating a colour composite signal isn't trivial, creating three separate mono signals and having the MC1377 do the heavy lifting of encoding them is a lot simpler then you feed it to a modulator.I'm amazed you can still buy modulators!

author: vk6zgo
author_rank: Super Contributor
timestamp: February 23, 2019, 04:13:33 am
content: If your country was the same as Oz, you could buy "set top boxes" which would receive terrestrial digital TV & output composite analog video & sound.If you had one of those (there are still probably a few around), you could plug its outputs into a modulator to achieve a signal your receiver could use.The modulators are designed to provide a low level signal to your TV antenna input via coax cable.If you stick a bit of wire in the modulator's output, you could probably radiate the signal & receive it across the room, but it seems to me to be going a bit overboard.After all, all the same circuitry is used in the receiver with a direct cable connection, & it is less likely to be noisy or "ghosty"!Other sources of composite video are older DVD players, analog CCTV cameras ,etc.Except for physical size, whichmightbe important, it is a lot less hassle using such things rather than to start from scratch.

author: radiolistener
author_rank: Super Contributor
timestamp: February 23, 2019, 04:58:10 pm
content: The modulator can be used to connect some kind of video equipment to the old TV, for example video camera or game box or something like that. So I think it should not depends if your country has analog TV or not. In both case the modulator can be available in the store with no legal issues

author: IanB
author_rank: Super Contributor
timestamp: February 23, 2019, 05:10:17 pm
content: Since TV went digital, you became able to buy "set top boxes" that would receive the digital signal off air and output an analog VHF signal for connection to the antenna input of analog TVs. Since they tried to maintain backwards compatibility with the VHF TV signal, I think this signal will be receivable by even very old TVs. So you could just obtain one of these boxes.(In the UK it is slightly different, since analog television switched from a 405 line system on the VHF band to a 625 line system on the UHF band. Very old British televisions designed for VHF wont work with the more recent UHF signal. But I don't think such a change happened in North America.)

author: janoc
author_rank: Super Contributor
timestamp: February 23, 2019, 07:42:43 pm
content: Quote from: radiolistener on February 23, 2019, 04:58:10 pmThe modulator by itself is not illegal, it is meant to be connected to the TV's antenna jack by a length of coax. However, once you start considering hooking it up to an antenna, that's a very different matter.

author: tkamiya
author_rank: Super Contributor
timestamp: March 07, 2019, 02:46:12 pm
content: Any old VCR/VTR will have an RF modulator at the end. You can pick one up from Good Will stores. Making composite signal is easy with a cheap EBay devices.Unless someone does crazy things like huge antenna or power booster, isn't output power is so small, it falls under incidental transmitters category? I wouldn't do it though. It will require me to re-study FCC rules to exactly find out what the rules are for license-less transmission and be able to measure it. Just in case...If you are talking about coax connection, you are safe.

author: janoc
author_rank: Super Contributor
timestamp: March 08, 2019, 03:15:52 pm
content: Quote from: tkamiya on March 07, 2019, 02:46:12 pmDon't think so.QuoteIf you connect an antenna to an RF source it would be a rather difficult argument to make that this isn't intended to radiate ... There is the part about causing interference as well.

author: jonovid
author_rank: Super Contributor
timestamp: March 08, 2019, 04:28:25 pm
content: the good bad and ugly of RF TV Modulators. IMO!many of the first video cassette recorders VCR's TV input RF Modulator gave the strongest signal befor ACMA then PMG / US FCC regulations capped the output level.it was known for ch-0 46MHz or ch-1 57MHz RF Modulator to send a signal upto 5 meters (20 foot) away, with just a wire coat hanger stuck in the RF out socket.so 1980's story's of people getting the neighbors, VCR TV output in the next room or apartment showing an adult movie.1980s 2 ch Modulatorand a aliexpress Modulator of today