
This was the most common system used by the Army in the second half of WW2.
http://en.wikipedia.org/wiki/AN/MRN-2From Wiki
"The set is a ground mobile, two course, VHF aural Radio Range with station identification, periodic sector identification and simultaneous voice transmission. it is a crystal controlled set and operates in the frequency range of 100 to 156 Mc. for use in guiding aircraft equipped with VHF radio receivers, such as SCR-522, to a landing field, or for use along ferry routes. effective range is 100 Miles."
This is a description of the aural radio range from the SCR-277
"In operation the transmitter sends out signals coded "A" or "N" in each of the four quadrants around the beacon. The signals overlap on the range, providing the pilot of the aircraft an indication of his position in relation to location of the beacon. Thus, if he is heading toward the beacon he will receive an aural signal coded "A" or "N" if he is between the beam, and when he is on the beam he will receive "AN" signal."
It was common for a pilot to get disoriented listening to the "A" or "N" in Morse code, and fly the reciprocal course by mistake.