433 MHz Band (LPD433 / ISM)
The 433.05–434.79 MHz range is a common sub-GHz band allocated to short-range devices in Europe. Because the wavelength is about 69 cm it reaches behind obstacles better, and a quarter-wave antenna is about 16 cm long. The permitted output power and conditions of use are subject to national regulation.
The band's standout aspect is its physics. A lower frequency means a longer wavelength; diffraction is more effective and the shadow region behind an obstacle is shallower than at 2.4 GHz. Free-space path loss at the same distance is also lower: at 100 m about 65 dB is calculated for 433.92 MHz and about 80 dB for 2.45 GHz.
- Antenna: a quarter-wave wire antenna is about 16 cm; to fit it into a compact remote control a helical antenna is generally used, and the price of that is a loss of gain.
- Congestion: the band is shared with garage remotes, car keys and telemetry devices; occupancy can be high in residential areas.
- Bandwidth: being narrow, it is not suited to high data rates and wideband spreading techniques.
Conditions such as output power, duty cycle and channel usage vary from region to region; the limits under which a device was placed on the market are written in its declaration of conformity and on its label. Since the dump data contains no band information for AXI's ST and SF series, the product label should be consulted for the frequency of these sets.
Context in which this term is used: 433 MHz or 2.4 GHz?