Abstract :
The following paper describes the development of simple experimental direction-finders for wavelengths between 6 and 10 metres, and their use in an investigation of the accuracy of direction-finding on these wavelengths. It is shown that the inherent accuracy of the instruments is well within the limits of ? 2?, while their sensitivity is sufficient for observation on an experimental 50-watt transmitter at ranges up to 22 miles over flat ground. Bearings have also been taken on signals emanating from London television transmitters, blindlanding beacons, and also from commercial and amateur transmitting stations some 3 000 miles away. Detailed experiments have shown that the site on which the direction-finder is used must be clear of obstacles, particularly trees and vertical wires, for a radius of at least 50 to 100 yards; and there are indications that similar conditions are necessary for the site of the transmitter. When such conditions are satisfied, the bearings observed at distances up to 22 miles from the transmitter may be in error by as much as 8?, although in the majority of cases the error was less than 2?. Such errors tend to diminish in magnitude as the range increases, and they may or may not be affected by small changes in position of the direction-finder, by changes in frequency of the transmitter, or in the orientation of the transmitting aerial. For a given set of conditions the changes in bearings observed from day to day do not exceed about 2? for ranges of 20 miles, although in some long-distance observations made on signals from American stations at a range of 3 000 miles the variations in bearings were much larger. A brief study has been made of the behaviour of the loop direction-finder when horizontally polarized waves are emitted at the transmitting station. It is shown that the errors experienced in this case can be almost entirely eliminated by the use of a rotating spaced vertical aerial arrangement in place of the loop. The evidence resu- lting from the use of this Adcock type of direction-finder indicates that the errors with the loop set are due to the reception of horizontally polarized waves.
