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