Frequency Hopping Spread Spectrum vs Fixed Frequency
Wireless remote controls use either a fixed frequency (FF) or a Frequency Hopping Spread Spectrum (FHSS). A lot of Elsema’s remote controls operate on five frequencies, and customers ask about the benefits of doing this versus using a single frequency.
Fixed frequency remote controls use a single frequency channel to transmit and receive the data. In each region of the world there are licence free bands (ISM Bands), for example Australia and Europe is 433 MHz or USA is 915MHz. Licence free bands are usually used by the public and if you get two or more users in the same area using the same frequency the transmissions are corrupted. A corrupted transmission normally causes the receiver not to be activated when the remote control button is pressed.
Frequency Hopping Spread Spectrum (FHSS) does exactly what its name implies – the carrier is automatically changed to hop from frequency to frequency. This allows the transmission to occur over several frequencies which allows the data to tolerate a significant amount of in-band interference providing that it affects only part of the spectrum. In general, if 1, 2 or even 3 frequencies are interfered in a 5 frequency hopping system it will still operate at its full operating range.
Since each FHSS remote control has its own frequencies and hop sequence, the chances of two remotes on the same frequency is greatly reduced. In the event of a hop clash, those remote messages are corrupted, however the probability that both remotes will hop to the same frequency a second time is very low. Therefore, a FHSS remote control system is more immune to interference when compared to a single or fixed frequency remote control system.
The left diagram shows a spectrum analyser of a fixed frequency (FF) and the right diagram shows 5 frequencies hopping over a time domain (FHSS).