The very old, early consumer TV remote controls used ultrasonics. They used the principle of small hammers striking some little metal bars inside. Each bar was resonant at a particular frequency. The receiver would follow its command according to the frequency it was recieving. These remotes are no longer available. The same is for many of the remotes for the early models of sets. The next generation of remotes used IR (infared). They tranmit the command data over an IR beam. All the new remotes are using IR for their data transmission.
There is a newer generation of remotes that will be coming on the market in a few years. These are going to be using 2.4 gHz RF (radio frequency). The data will be sent on an RF carrier. This is going to soon be low in cost for the manufactures to achieve. It will also be able to through walls, and around corners, because it is RF, and not optical as like the IR type transmission. Each TV set will be able to address its own security code, so that there will not be any conflicks or crosstalk.
The best place to find the very old remotes are at the flea markets. Sometimes you can find them at a garage sale. The only problem, is that it has to be the right one for your set. I tell people that since the prices are very cheap at the flea markets, they should buy a number of them when possible. This way there will be parts to make one out of a number of them.
When I was about 8 years old, I saw a remote control TV for the first
time. This was very facinating for me. This was back in the 1950's.
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