Ground Based Direction Finding [D/F]
is similar to the aircraft based system but more powerful as bigger / more powerful installations were possible. The aircrew, perhaps the radio operator, held the Morse key in transmit mode for a minute while the ground operator took a bearing on the signal. If two ground stations were used, the point at which the bearings intersected produced a nav fix.
In the 1930's the onboard aircraft transmitting equipment included a 250 ft trailing aerial that was unwound after takeoff and
wound in before landing. Sadly, Amelia Earhart left hers behind on the fatal flight.
These ground based D/F stations were still listed on pilot charts up to at least the late 1950's. The DF code in the airport's text box indicated the D/F facility.
The Marconi Adcock D/F installation as used by Pan Am at their Pacific Island bases had a range of up to 1,500 miles over the ocean. These Pan Am bases were established in 1935. [John G. Borger]
The Pan Am Pacific bases were Honolulu, Midway Is, Wake Is, Guam, Manila for the Asian route. The South Pacific route from Honolulu was Canton Is than Noumea to Auckland.
The Auckland Adcock base was called Musick Point after Capt Edwin Musick, the pioneering Pan Am pilot lost when the Pan Am S-42B "Samoan Clipper" disappeared January 1938.
[Gwynn-Jones P.215] [Parnell / Boughton P.122]
In 1937 Australian Marconi Adcock bases were planned for; Cooktown QLD, Port Moresby PNG and Salamaua PNG. [Parnell / Boughton P.166]
1935 saw AWA establish a D/F station at Essendon Airport, Melbourne, using
Bellini-Tosi equiptment. More Australian ground based D/F stations were soon built at other locations in Australia. [Job 1991. P.127]
The 1939 map of Australian D/F bases and air routes is
available for viewing. (please note this contains a 181kb gif image) [Job 1991.
In addition, radio facilities were also established at Lord Howe Island in the Tasman Sea, between Norfolk Is and Sydney. [Parnell / Boughton P.122]