What is the difference between the 433 MHz and 868 MHz bands?
In the 433.050-434.790 MHz band the permitted power is 10 mW e.r.p. and, for systems without frequency hopping, the duty cycle is limited to 10%. In the 868 MHz sub-bands the power rises to 25 mW e.r.p. but the duty cycle drops to 1% or 0.1%. The lower frequency diffracts better behind obstacles, the higher frequency needs a shorter antenna.
The difference between the two bands is a trade-off; neither is superior in every condition.
The regulatory side (the ERC/REC 70-03 and ETSI EN 300 220 framework):
- 433.050-434.790 MHz: 10 mW e.r.p., duty cycle ≤ 10% for systems without frequency hopping.
- 863-865 MHz: 25 mW e.r.p., duty cycle ≤ 0.1% or polite spectrum access.
- 868.000-868.600 MHz: 25 mW e.r.p., ≤ 1%.
- 868.700-869.200 MHz: 25 mW e.r.p., ≤ 0.1%.
The physics side: the wavelength at 433 MHz is longer; diffraction around obstacle edges is better, meaning it wraps around a concrete corner more easily. The price is a longer antenna for the same efficiency. At 868 MHz the antenna gets shorter and the permitted power is higher, but the duty cycle limit prevents continuous transmission.
Important note: the operating frequency is not stated in the product records of the AXI ST and SF sets. Confirm which band your device works in from the product label and the user manual; the information above is general regulatory and RF information about the bands.
The full topic: 433 MHz or 2.4 GHz?