Are there channels on 433 MHz?

Hi, I have some experience with nRF24L01+ and I know it is "2.4 GHz" but in reality it transmits at one of 125 channels nominally starting at 2.400 GHz with 1MHz increments. WiFi also uses similar frequency channels. Now I do some experiments with "433MHz" and I wonder - is it a single channel or are there some close channels too? The cheap 433 MHz Tx/Rx eBay devices have no option to change the frequency but more advanced like SI4432 can tune the frequency by changing some registers in similar way as the nRF do. What does it mean?

Smajdalf: Are there channels on 433 MHz?

I wonder - is it a single channel or are there some close channels too?

Its a frequency allocation, a range of frequencies you can use, and the exact frequencies you can use varies depending where you are in the world.

There is no univerasal allocation of 'channels' that I am aware of.

I have problems to formulate what I want to know, I will try it again from the other end.

There is plenty of "433MHz" devices. What exact frequency are they using? Are they all compatible with each other? Are they using the same frequency so Rx and Tx device from different sellers should (try to) send and receive on exactly the same frequency? We have a 433MHz rain gauge. Should a generic Rx be able to "hear" data from the gauge and a generic Tx to "be recognized" by the base of the gauge? What about remote of garage door and similar?

There is plenty of "433MHz" devices. What exact frequency are they using?

Depends on the device, some may be used on a few limited frequencies, some can be configured for any frequency in the band, such as SI4432, SX1278 etc.

Are they all compatible with each other?

No.

Are they using the same frequency so Rx and Tx device from different sellers should (try to) send and receive on exactly the same frequency?

No.

We have a 433MHz rain gauge. Should a generic Rx be able to "hear" data from the gauge and a generic Tx to "be recognized" by the base of the gauge?

No such thing really as a 'generic' 433Mhz device. A lot of the simple\cheap 433Mhz devices use AFSK, the more sophisticated devices such as SI4432, SX1278 wont recognise AFSK.

What about remote of garage door and similar?

Depends on the device, there is a wide range of '433Mhz devices' some might be compatible with each other some might not.