How does the duty cycle limit affect the remote control?
The duty cycle is the maximum proportion of time a device may stay transmitting within a given period. In the 433.050-434.790 MHz band the limit is 10% for systems without frequency hopping, and 1% or 0.1% in the 868 MHz sub-bands. The purpose of the limit is to stop devices sharing the band from drowning each other out.
Short range devices operate in licence-free and shared bands. Nobody owns the band; for everyone to be able to use it, everyone has an obligation to stay silent. The duty cycle limit is precisely that obligation to stay silent.
What it means in practice is this: in a band with a 10% limit a device may transmit a total of 6 minutes in every hour. This does not mean a continuous data stream; the remote control sends short packets for as long as the button is held and stays silent in between. A well-designed industrial remote control repeats the command in packets a few milliseconds long and keeps the total transmit time below the limit.
Consequences on site:
- If there are many devices in the same band, channel occupancy rises; range and response time fall. This is not a clash — because every set has its own identity code the commands do not get mixed up, only the air traffic gets busier.
- On busy sites, raising the receiver antenna and moving it away from interference sources is more effective than increasing the transmit power; the power is already limited by legislation.
- Other equipment transmitting continuously (telemetry, wireless sensor networks) can fill the same band; assess the site before installation.
The full topic: Wireless Crane Remote Control Selection Guide