Airways Museum Virtual Tour - Bellini-Tosi MF DF
Whist the aircraft's radio operator transmitted, the Aeradio operator would use the goniometer at bottom left to tune the antenna system until a null was heard in the signal. The dial would then indicate a bearing to the aircraft.
As two nulls would occur 180 degrees apart, the operator was able to resolve this ambiguity using a 'sense' switch which enabled determination of the correct bearing. Since a DF bearing could only fix the aircraft's position along a line of bearing from the station, bearings from more than one station were required to determine the aircraft's actual position.
Operating in the MF band, the Bellini-Tosi equipment suffered from atmospheric interference, and sometimes unreliable bearings due to coastal and night effects caused by radio signal propagation changes. For this reason the Bellini-Tosi equipment was supplemented from 1939 by the Adcock HF DF system which gave more reliable performance.
Click here to find out more about the B-T MF DF system
(Photo: CAHS collection)