MOST of the transmission methods used today are rather elementary. The signal to be transmitted is made to vary the amplitude or phase of a sine wave, or perhaps the height, width, or position of a pulse. The variation is continuous, and at each repeater some noise, cross-talk or distortion is added to the signal, causing some deterioration in quality. By the time the signal has gone through hundreds of repeaters, it is a miracle that there is any quality left.