Frequency (Hz)
Frequency is the number of cycles a wave completes per second, measured in hertz (Hz). 1 MHz means one million and 1 GHz one billion cycles per second. The values used in remote control bands — 433 MHz, 868 MHz and 2.4 GHz — directly determine both the range character and the antenna length.
As frequency rises the wavelength shortens, because the product of the two equals the speed of light. In practice this has three consequences.
- The antenna gets smaller: a quarter-wave antenna is about 16 cm at 433 MHz and drops to about 3 cm at 2.45 GHz.
- Path loss increases: at the same distance, 2.45 GHz produces about 15 dB more free space loss than 433 MHz.
- Bandwidth becomes plentiful: at high frequency it is easy to allocate wider channels, which means higher data rate.
In a remote control application the data to be carried is a few bytes; the need is not high speed but a link that survives behind obstacles. That is why sub-GHz bands are advantageous for range, while 2.4 GHz is suitable for bidirectional and frequency hopping protocols. The XRF protocol used in AXI's HCT400 and HCT402 sets works with frequency hopping at 2.4 GHz; for the band of the ST and SF series, check the product label and the declaration of conformity.
Context where this term is used: 433 MHz or 2.4 GHz?