sentences:  Around 1905 the first continuous wave radio transmitters began to replace the earlier spark transmitters.The Morse code signal of the spark transmitter consisted of pulses of radio waves called damped waves which repeated at an audio rate, so they were audible as a buzz or tone in a receiver's earphones.In contrast the new continuous wave transmitters produced a signal consisting of pulses of continuous waves, unmodulated sinusoidal carrier waves, which were inaudible in the earphones.