Are there generic generic repeaters for 433 MHz communication (such as for doorbells)?
The band isn't standardized and what equipment that's allowed on it differs from country to country. In EU where this band is most popular, you have a EU-wide directive that's regulating the 434MHz band, but individual countries are allowed to make exceptions. There are more specific rules for 433MHz than for 434MHz in EU, though in many countries these are regarded as the same band.
Outside EU it turns even more complicated, since every country has it's own rules for spectrum allocation. In North America and South-East Asia you can barely use the band license-free at all. For example several countries have reserved the band for cargo container tracking systems/RFID.
Apart from the lack of standards and international legislation, it is not possible to make a &quot;generic repeater&quot; simply because it is a license-free band, where any form of signal is allowed. Imagine the following scenario:

In a central location of a city, you have 434MHz transmitters for doorbells, thermometers, telemetry, car locks, garage doors, radio amateurs, &quot;smart&quot; homes etc etc. So the band is already quite crowded.

A new building site is put up nearby. This means numerous cranes, pile drivers, trucks and other machinery using this band too. And they all use continuous transmission since they are control systems. You'll have things like concrete trucks coming in at any time, each with a 434MHz remote. Overall some 10 new remote systems on the band, in addition to what was already there.

Now someone invents a generic repeater which just scans the band for anything that appears to be a digital signal, of any bandwidth, with any modulation, then repeats the incoming signal the best it can with the maximum allowed output power (generally 10dBm E.R.P), at the same bandwidth. It will have to be very smart because signals could be modulated as FSK or ASK or OOK or something else... Where each modulation technique comes in different flavours: 2-FSK, 2-GFSK, 4-GFSK- 6-GFSK etc etc...

If they somehow get this repeater working as intended, then that means all of the mentioned sources will have their signals amplified in whatever direction the repeater is set to point (either directional or omni-directional). This will lead to a massive increase of local signals on the band. Because normally all these transmitters may only have some 10 to 100m range or so, after which they wouldn't really interfere with each other much. But because of the repeater, we potentially have every device in the area interfering with each other suddenly. With the result that no communication in the area will be possible at all - turns out we haven't actually invented a repeater but a signal jammer.

And congratulations, this repeater has now not only blocked the 434MHz band but is also causing major disturbance on the 868MHz one where the first harmonic ends up.


You can design repeaters for the band but they have to be specific for a certain equipment, as is the case for Wi-Fi. All the repeaters you have linked are specialized for a certain kind of signals.