Page 124 - Electronic Navigation Cyber Book

RADIO DIRECTION FINDING

With the advent of the GPS and the massive leaps forward in
microelectronic technology, the system of radio direction finding (RDF)
looks distinctly aged.
It is, the oldest of the position fixing systems having been around in one
form or another since the First World War. RDF systems used throughout
the last century owed their existence to Sir R. A. Watson-Watt who
invented the original concept and to Adcock who designed the non-
rotating antenna system that eliminated the earlier troublesome
mechanical rotating antenna. To this day, RDF system principles remain
unchanged, it is the signal processing and computing functions offered
by modern microelectronics that has propelled RDF into the 21st century.

Once the mainstay of maritime position fixing the medium frequency RDF
receivers and the large loop antenna that once dominated a ship's
superstructure, have now been assigned to the scrap heap. But RDF is
still alive and modern vessels do carry VHF RDF equipment. It is still an
efficient system for localized position fixing and remains the only method
for finding the bearing of a transmitter in an unknown location. If the
relative bearings taken by two suitably equipped ships are laid-out on a
chart, the two bearing lines will intersect at the position of the unknown
transmitting station. Such a station need not be a radio beacon. It could
be a vessel in distress and thus the two receiving ships are able, by
triangulation, to pinpoint the distress position at the intersection of vectors
drawn on a chart from their two known locations. Naturally, the same
holds true for two land-based RDF stations.

© 2018 Digital Galaxy Index 124