A description is given of a simple U-type rotatable radio direction-finder, which was used to investigate the improvement in performance of short-wave direction-finders obtained by the use of large earth screens, and to determine the smallest ratio of screen-size/wavelength for which the polarization errors were reduced to a satisfactorily small value (≃1 deg).The screens were constructed of sheet metal, wire netting and radial wires, and the results showed that provided a metal sheet was not less than 4λ in diameter, polarization errors as small as 1 deg could be attained. For wire-netting screens of the same diameter, a mesh size not greater than ½ was required to attain this performance.