A) The ratio of on-air time to total operating time of a transmitted signal
A duty cycle is the time that a device spends in its active state as a fraction of the total time under consideration. In an amateur radio and RF safety context, the term is used with reference to transmitters. So a transmitter's duty cycle is the time a transmitter is functionally transmitting in a specified period of time. Different operating modes have different duty cycle characteristics since the RF being radiated is often intermittent. A lower duty cycle reduces the average exposure to the RF radiation.
Examples of operating mode typical duty cycles:
- CW = 40%
- SSB voice = 20%
- FM = 100%
Average power = PEP x operating cycle x (transmitting time / averaging period)