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High-frequency direction-finders (operating on a frequency band of 1.5 to 30 Mc/s) have been used extensively during the war for shore station d.f. networks. The aerial system employed has been almost exclusively the buried-U Adcock type. The main considerations for using this type of aerial system were as follows:- (a) Small polarization error. (b) Wide frequency-band coverage. (c) Adequate sensitivity. (d) Suitability for use either with radiogoniometers or cathode-ray type direction-finders for rapid bearing indication. The main developments in h.f. direction-finding have been in the reduction of polarization error by the use of earth screens, and an attempt to reduce phase interference effects by ray-separation technique. Improved methods have also been devised for aerial balancing and for compensating for instrumental irregularities. In this connection an internal injection method has been developed for checking the overall balance of aerials, feeders and radiogoniometers, especially for use on sites where an external local calibrating transmitter is unreliable. Attention has been paid to improvements in design of radiogoniometers, and instruments have been developed for injecting calibrated voltage ratios into the field coils for laboratory checks of instrumental performance. A special type of local calibrating transmitter has been developed which employ frequency modulation for rapid local calibration checks and more especially for sense circuit calibrations. This has proved extremely useful in detecting minute aerial irregularities occurring over narrow frequency bands. An investigation has been carried out into the operational performance of various d.f. systems on all classes of traffic. A comparison has been made of the merits of visual and aural presentation and their effect on accuracy, speed of operation, flexibility and simplicity of maintenance. The advantages of group station working are discussed, and finally a type of instrument is described the d- esign of which is based on the results of operational statistics.