What is duty cycle (transmission time ratio), how does it affect the remote control?
Duty cycle is the upper limit on how much a transmitter may transmit in total within a given period. A 1% duty cycle means 36 seconds of transmission per hour, a 10% duty cycle means 360 seconds. In Europe the typical limit is 10% for 433.05–434.79 MHz and 1% for most sub-bands of 863–870 MHz; at 869.4–869.65 MHz 10% is allowed with 500 mW ERP.
The duty cycle limit is imposed to stop devices sharing a band from choking each other. The limit originates from ERC/REC 70-03 and the measurement method is defined in EN 300 220-2 (current version V3.3.1, 2025-03).
The practical effect on the remote control side is this: a design that sends packets continuously as long as the button is held down cannot work more than 36 seconds per hour in a sub-band limited to 1%. That is why real products:
- Keep the packets short and leave gaps between them.
- Stop transmitting when the button is released and put the transmitter into sleep mode.
- Run a timeout counter on the receiver side; if no valid packet arrives within the set time, the outputs are brought to a safe position.
This last item is where duty cycle and safety intersect. For example on the HCT402 the signal loss protection works with a 250 ms timeout: if no valid packet arrives within that time, the motor goes to the safe centre position and oil flow stops.
A device exceeding the duty cycle limit is transmitting contrary to the regulations despite its declaration of conformity; in applications requiring a permanent connection, alternative access methods such as LBT+AFA are preferred.
Full article: Wireless remote control installation: pairing, relay, safety