Why did old TVs require that the channel be on 3 before accessories like VCRs and game consoles could work on them?


Anyone who grew up in the CRT era of TVs remembers that you had to turn the channel to 3 before you turned on the VCR or game console. Otherwise, the picture would not work. Why was this so necessary?

Edit: woah this blew up while I wasn’t looking! Thanks for the replies!

In: Technology

The accessory had a built inn TV transmitter. It would not output a high power signal so you could not use it to transmitt the signal over the air very far. But if you connected it to the antenna cable in your house it would be picked up by the TV. You would often be able to select what channel to transmitt on which would have to match the channel on your TV. But some channels such as channel 3 and 7 were common ones. This would be so that you did not accidentally transmitt on the same channel as your local TV station as then you would not be able to watch this TV station.

You would have your normal cable line that had all the channels on it. You would plug this into your VCR. You plug another cable from your VCR into your TV.

When your VCR was idle, it would just forward the signal from its line in onto its line out. However, when your VCR was on, it would interrupt the signal for one channel and put its own signal on that channel instead.

Channels on old CRTVs that had TV *tuners* are basically different frequencies that you tune your TV to, like how you turn your radio to a specific frequency to pick up a channel you wanted to listen to.

Edit: it was channel 3 (or the selectable alternative to avoid interference) because the NES/VCR had to be talking in the same “language” (channel 3 frequency 60-66 MHz, channel 4 frequency 66-72 MHz, or channel 5 frequency 76-82 MHz depending on where you live and which had the least interference for you).

Back in that day we had no way of transmitting the image and sound from the game console or VCR directly to the TV like we do today with S-video, component, HDMI, Display port, etc. So the simple solution was to turn the image and sound into radio ~~waves~~ frequencies and transmit it to the TV like a TV station. To comply with Federal regulations this TV signal from the console would have to be very weak so that it wouldn’t interfere with any other signal. This means that the console could only transmit the signal a few millimeters to centimeters. To get around this limitation they used coaxial cable to carry the signal but you still had to tune the TV into the frequency the console/VCR was transmitting at.

This guy does a good job explaining that a NES and similar devices are actually mini TV transmitter stations. [~~https://youtu.be/8sQF_K9MqpA~~](https://youtu.be/8sQF_K9MqpA) [https://www.youtube.com/watch?v=8sQF_K9MqpA](https://www.youtube.com/watch?v=8sQF_K9MqpA) (I’m not sure what’s going on with URLs today, people are saying my link is broken but when I click on their links, I get the exact same URL that I posted…)

Edit: this really blew up. To clarify some things:

* I accidently put radio ***waves***, the NES doesn’t transmit (yes it’s a transmitter) radio waves, it transmits electric Radio Frequency (RF) to the RF modulator/adaptor that translates that signal into the frequency range used by the selected channel. (There’s probably something I don’t understand about this as I understand modulation is changing the frequency rate to transmit more and varied information u/maxwellwood did a great job expounding on this [here](https://www.reddit.com/r/explainlikeimfive/comments/nud63i/eli5_why_did_old_tvs_require_that_the_channel_be/h10vhzt?utm_source=share&utm_medium=web2x&context=3)).
* Technically speaking anything that transmits electric RF also inadvertently transmits radio waves in the form of electromagnetic RF radiation. This is mitigated. Blocked by what is known as shielding.
* Yes, I know about the two screw antenna connection. Technically, a coaxial cable is that two screw connection bundled into a single, shielded cable with a universal/standardized connector.
* Yes, you can transmit your game console’s frequency over the air to your TV with the appropriate Electric RF to electromagnetic RF amplifier. All electric RF produces radio waves as far as I’m aware whether on purpose or not. Doing this while remaining in the grey area of legality in most countries would get you a pretty crappy signal to the TV though at any distance you couldn’t just use the cable.
* All cables used to take audio/video (AV, A/V) from a device to a TV is a transmission of data regardless of electric verses electromagnetic.

Very similar to those audio device adapters which transmit on particular FM station frequencies, it’s a very very localized pirate radio station.

Except the switchbox was a direct interface to the antenna input, and did not transmit into the air. Channel 3 is a particular frequency and was commonly unused in most places (over the air) so there would be less interference/collision. If you area did have a channel 3 over the air then you had the choice of 4. And no market had channels immediately next to each other due to bleed-over, so if you had a 3 you didn’t have a 4 or if you had a 4 you didn’t have a 3. Usually the channels were 2,5,7,9,11 or such, nicely spread out, many markets didn’t have a 3 OR 4 at all.

Of course when over the air was mostly replaced by cable, there was less need for channel separations. And digital has no neighbor-bleed problem at all.

Older TV sets did not have inputs for devices. They could only display pictures that came in as TV signals. So the devices had to emit a TV signal.

TV signals have to be on some channel. By convention channel 3 was used (only a few areas had a Channel 3 station).

When TVs were invented, it never occurred to the manufacturers that they could be used for anything besides broadcast content from regional television stations. That’s what they are set up for: VHF broadcast reception within several predefined channels.

When the first home video devices were invented (VCRs, computers, video games, etc) the only way for your television to recognize the signal was if the device in question created a signal identical to what the broadcast station would create.

Conveniently, most televisions had the ability to connect an external antenna in the back. All your device had to do was convert the desired composite video into an NTSC broadcast signal with appropriate levels, and feed it into an antenna cable, which you wired directly to your television.

The last step is telling your television where to find the signal. Most devices broadcast on either channel 3 or channel 4, and there was usually a switch on the back to choose.

It’s a cultural thing. In the UK we had two dedicated AV channels which didn’t take up existing channel slots. And as far as I can tell, this is still the case for TV that don’t have digital channels built into them.

I never got this – all the analogue CRT TVs I had were tunable, I used to put the console on channel 6 because we had 4 TV channels and I’d put the VHS on 5. Did American TVs not let you do that?

Is this a US spesific thing? Cause I had several CRTs growing up, the oldest one being from the 70s (which only has 2 tunable channels), and every one of these would work directly with game consoles.

Atari 2600 had a switch for 3-4 in case the channel 2 in the area was too strong and interfered with 3.

Here’s a cable TV company [“Keep It On 3”](https://www.youtube.com/watch?v=QYOImTAV4Zg) customer education series of commercials from 1995, produced so that people with cable boxes didn’t tie up the Customer Service lines, and trigger truck rolls, just because they didn’t have their damn TV sets on Ch 3.

OK, I made this. I went nuts. Managers gave me this assignment, they expected just a single commercial, perhaps with a service tech, wearing hardhat, standing in front of his van, saying: “Please keep your TV set on Channel 3.”

Instead they got this.