Site and Path Errors in Short-Wave Direction-Finding

The paper deals with the results of a series of investigations into the errors observed in short-wave direction-finding on wavelengths of 20¿50 m 6¿15 Mc/s). It is shown that the errors observed on a transmitter at a distance of several miles vary rapidly and erratically with azimuth, wavelength and distance. In some cases a change of bearing of 2¿3 deg has accompanied a change in azimuth of 0.5 deg or a change of wavelength of only 1%. It was also found that for two different sites the average numerical error and the (statistical) probable error were roughly proportional to the wavelength. For one site, the probable error on a wavelength of 50 m (6 Mc/s) was 1.7 deg and on 30 m (10 Mc/s), 0.8 deg. A hypothesis is put forward to explain these results on the basis of an assumption that the errors are due to re-radiation from a large number of reflectors scattered at random over a considerable area around the direction-finder. The implications of such a theory are discussed, and it is deduced that for average sites the probable error will have a maximum value on a wavelength of about 100¿150 m. Some tests, carried out with a portable direction-finder, show that even on apparently ideal sites, the local errors are not always negligible.