Each Adcock range station had four 134-foot-tall (41 m) antenna towers erected on the corners of a 425 × 425 ft square, with an optional extra tower in the center for voice transmission and homing.[1][2][3] The stations emitted directional electromagnetic radiation at 190 to 535 kHz and from 50 to 1,500 watts, into four quadrants.[4][19][note 2] The radiation of one opposing quadrant pair was modulated (at an audio frequency of 1,020 Hz) with a Morse code for the letter A (· —), and the other pair with the letter N (— ·).[note 3] The intersections between the quadrants defined four course lines emanating from the transmitting station, along four compass directions, where the A and N signals were of equal intensity, with their combined Morse codes merging into a steady 1,020 Hz audio tone. These course lines (also called "legs"), where only a tone could be heard, defined the airways.[17]