Why particularly 433.92 MHz is used in RF transmitter and receiver?

Answer 1

RF Code first began offering products in the 303MHz range (US & Japan) and later in the 433MHz range (US & Europe). These signal frequencies are limited, low-power, unlicensed ranges in the ISM (Industrial, Scientific and Medical) portion of the UHF band. RF Code began offering 433MHz products because of acceptance of this frequency in Europe. 433MHz is also the frequency which offers optimal performance in crowded environments such as offices, data centers, and hospitals.

Generally, radio signals at lower frequencies travel farther than those at higher frequencies. Lower frequencies also benefit more from the effects of reflection and refraction which makes them more suitable for applications in crowded environments. For example, the 433MHz wavelength is approximately 69 cm vs. 10 cm for 2.4GHz. The larger wavelength of the 433MHz signal allows it to diffract around obstructions that might be found in a typical, crowded operating environment such as an office or warehouse. At frequencies of 2.4GHz and above, the signal is susceptible to obstructions, creating blind spots (areas of no coverage). Higher frequencies also require more power.

Answer 2

433MHz (433.92MHz in fact) is the most used frequency on earth. It's a free use unprotected Short Range Devices frequency used by a lot of devices.

To name a few, car keys, door openers, external wireless thermometers

and pressure sensing devices, radio ham TV,... and

wireless alarm systems.

Answer 3

The FCC has set-aside certain frequencies for certain uses. Some frequencies require licenses and others are allowed to operate unlicensed if they meet certain parameters (usually power level and type of transmission). 433.92 Mhz has obviously been set-aside for unlicensed use for low power data transmissions, which is why so many devices use that frequency for that purpose.