The specification and measurement of polarization errors in Adcock-type direction-finders

This critical review of the specification and measurement of polarization errors in Adcock-type direction-finders was prepared in 1944. The respective merits of the ¿standard-wave error¿ introduced by Barfield, and the ¿pick-up ratio¿ for wanted and unwanted fields suggested by several other workers, are examined. It is concluded and recommended that the former is to be used for Adcock direction-finders erected not higher than about ¿¿ above ground, while the latter is appropriate for more elevated systems. Comparison of direction-finders falling into different categories can only be carried out if a complete specification of polarization error performance over all relevant angles of incidence is available. The problems involved in using a relatively nearby test transmitter are discussed. For frequencies above about 3 Mc/s it is shown that a suitable local radiator consists of a rotatable closed loop used at moderate elevations, and at distances not less than a wavelength. The effects of loop size are discussed, and it is shown that adequately large loops are practicable; for example, for frequencies in the range 3¿30 Mc/s, a loop up to about 5 ft in diameter may be used, providing the distance is not less than 100 m. For frequencies below about 2¿3 Mc/s it is suggested that the ¿local-injection¿ method due to Barfield may be more practicable than a radiation method. It is pointed out that the performance of a direction-finder is in general intimately bound up with the electrical properties of the site on which it is erected.