 All modern high-power (>50 kW) shortwave radio transmitters incorporate DCC of some kind, as well as some mediumwave (MW) transmitters.DCC causes the carrier wave level to be automatically reduced when the audio is very weak or no audio is present.During periods of silence (no audio), the carrier power is reduced by 50%, so the 250 kW transmitter is putting out a carrier of 125 kW during audio pauses.