chapter  9
Automatic direction finder
Pages 1

The early airborne navigation systems using

ground-based navigation aids consisted of a

fixed-loop antenna in the aircraft tuned to an

amplitude modulated (AM) commercial radio

broadcast station. Pilots would know the location

of the radio station (indeed, it would invariably

have been located close to or even in the town/

city that the crew wanted to fly to). The fixed-

loop antenna was aligned with the longitudinal

axis of the aircraft, with the pilot turning the

aircraft until he received the minimum signal

strength (null reading). By maintaining a null

reading, the pilot could be sure that he was flying

towards the station. This constant turning was

inefficient in terms of fuel consumption and

caused inherent navigation problems in keeping

note of the aircraft’s position during these

manoeuvres! The effects of crosswind

complicated this process since the aircraft’s

heading is not aligned with its track.