2.4 GHz ISM Band
The 2400–2483.5 MHz range is the most widely used licence-free band worldwide. Its wide bandwidth makes it suitable for frequency-hopping and bidirectional protocols. Since the wavelength is about 12.2 cm the antennas are small, but in return it suffers more loss behind obstacles than sub-GHz bands.
The band has two clear advantages: bandwidth is plentiful so many channels can be opened, and the antenna is physically small. This allows frequency-hopping protocols to use a wide hopping space.
- Path loss: at the same distance there is roughly 15 dB more free-space loss than at 433 MHz; at 100 m about 80 dB is calculated.
- Behaviour behind obstacles: because of the short wavelength, the shadow behind concrete, metal and dense structures is deeper.
- Occupancy: the band is shared with wireless networks, personal devices and microwave ovens; frequency hopping becomes critical in this environment.
In Europe, use of the band is regulated through the relevant harmonised standard, and the commonly applied upper limit is 20 dBm, that is 100 mW equivalent isotropically radiated power. On the AXI side, the XRF protocol of the HCT400 and HCT402 sets works in this band with frequency hopping and bidirectionally; the dump data states a 100 m range for these sets.
Context in which this term is used: 433 MHz or 2.4 GHz?