FHSS (Frequency Hopping Spread Spectrum)
FHSS is the carrier hopping from channel to channel within the band according to a predetermined pattern. Transmitter and receiver share the same pattern and the same timing. A narrowband interference source corrupts only a few channels in the pattern; corrupted packets are discarded by the checksum and transmission continues on the next hop.
In a fixed frequency system, a continuous transmission landing on your channel blinds the link entirely. In FHSS the same source affects only a few steps of the hopping pattern; the remaining steps are clean and transmission continues from there.
- Hopping pattern: it can be derived from the device identity; when different sets use different patterns, the chance of collision on the same site drops.
- Synchronisation: the receiver has to lock onto the pattern and the clock, so establishing the link takes a little longer than in narrowband systems.
- Interference behaviour: a single corrupted hop appears as delay, not as a lost command.
The XRF protocol used in AXI's HCT400 and HCT402 hydraulic lever control sets uses this architecture: interference resistance through frequency hopping, bidirectional acknowledgement and a unique pairing identity per device are the features listed in the dump data. This structure makes it possible for more than one kit to work together on the same site.
Context where this term is used: 433 MHz or 2.4 GHz?