The Decca Navigator System, herein abbreviated as DNS
for convenience, is a hyperbolic radio navigation system which was established
in the United Kingdom after World War 2 and later used in many areas around
the world. It operated by measuring the phase differences between continuous
signals from a master and slave stations. These differences were then related
to a hyperbolic lines printed on a chart. By plotting the readings from
two pairs of hyperbolas at any particular instant, users could plot their
position instantly.
The system used groups of at least three shore based transmitter stations called chains operating in the 70-130 kHz radio band. Each chain comprised of one Master and two or three Slave stations, usually located 80 to 110 km from the Master station. The accuracy of DNS ranged from 50 meters during daytime to 200 meters at night. It could decrease up to 800 meters as the distance from the baseline increased. Accuracy was also affected by seasonal effects which generally reduced the accuracy by a factor of 6 to 8. The maxium daytime range for DNS was 300 to 400 miles with a reproducibility of 200 meters. At night, accuracy was guranteed out to 240 nm by the British Admiralty.
