The operator's console for the Bellini-Tosi Medium Frequency Direction Finder (MF DF). This was Australia's first standardised radio navigation aid. The system had the advantage of not requiring special airborne equipment, other than a standard radio transceiver.

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)

 

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