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Aviation History
1937
1937 - 1947.PDF
JULY 8, 1937. FLIGHT. 6t Commercial Aviation SHORT-WAVE DIRECTION FINDING Points About the New Marconi System : An Interesting Development for Long-range Work NOW that Atlantic experiments have actually started in real earnest, this appears to be an opportune moment to describe one of the many radio developments which have made such long-distance services a practical possibility. It is well known that really useful wireless ranges can only be obtained with short-wave equipment and the difficulty has so far been that of developing a direction-finding system which, with the use of such short waves, will still be reliable and accurate. The development and application in 1931, by Marconi's, of the Adcock principle to wireless direction-finding on medium wavelengths overcame the disadvantage of "night effect" — a natural phenomenon rendering other forms of D/F unreliable during the hours of darkness—and installations of this type have been put into service at nearly a hundred points. Until recently, however, the characteristics of wireless waves shorter than about 500 metres rendered them unreliable for D/F work with the available apparatus. Thus the very long ranges over which ordinary communication can be carried out with low- power transmitters on the short wavelengths were not avail able for direction-finding purposes. As an aid to aircraft navigation, direction-finding was limited to the comparatively short ranges obtainable with medium-wave aircraft transmit ters—normally less than 300 miles. The application, in short-wave apparatus, of the same prin ciples which eliminated "night effect" from medium-wave D/F, has, with equal success, brought short wavelengths with in the scope of accurate direction-finding services for long-range work. This feature is embodied in the Marconi Type DFg.12 installation, which covers a wave-range of 15-200 metres. A peculiarity of short wavelengths is that they cannot travel far over the earth's surface, The energy which reaches the distant receiver is that which has been radiated away from the earth's surface at an angle and after reflection from the " heaviside layer " has come down again at a distance from its source (technically known as the "skip" distance), which varies to some extent with different wavelengths. These wave lengths cannot be received for D/F finding or any other purpose except at very short or very long ranges. By good fortune it so happens that the distance at which many of the short wavelengths '' come back to earth '' coin cides with the maximum range normally obtained by a medium- wave aircraft transmitter—round about 300 miles. It fol lows, therefore, that aircraft equipped with both short- and medium-wave apparatus can now be served by a ground D/F station fitted with both types of installation at all times of I.C.A.N., 1937 A NUMBER of points were raised at the twenty-fifth session of the International Commission for Air Navigation, which was held between June 4 and 10 in Paris. Twenty-eight of the thirty-two parties to the 1919 Convention were represented. The following were among the more important questions to tie considered: (1) Standardisation of flying maps: Recom mendations had been addressed to the contracting States and the Commission had drawn up a new programme for the publication of the different sheets of the basic international map published by itself. It has been decided that a new map shall be prepared for D/F work. It has been recommended that established frontier air corridors should be clearly marked. (2) Meteorology : The States have been invited to increase the interchange of climatological summaries through the I.C.A.N. Secretariat. (3) Radio: The Commission has proceeded with the final drafting of the regulations for the international radio- electric service and incorporated a new set of rules concerning the direction of aircraft in bad visibility, prescribing compul sory radio watch-keeping. (4) Journey log-books: The Com mission has adopted a new model of the journey log which will be issued after April 1, 1938. (5) Fitness: New medical re quirements have been laid down in relation to visual acuity and colour perception in different categories. (6) Accidents: It has been decided to invite the States to publish retrospective statistics of air accidents which have occurred during the last ten years A model has been drafted for this purpose. The States have also been invited to exchange accident reports or the like from which useful information may be derived. The next session will be held in May, 1938. the day and night and at any distance up to 2,000 miles, or more, by the correct choice of wavelength to suit the time and distance. Needless to say, the key feature of this short-wave develop ment is the aerial system, which consists primarily of four vertical aerials situated at the corners of a square. The lay out is, in effect, that of two rectangular loops at right angles to one another, with the horizontal top members eliminated and the horizontal bottom members screened and buried—the latter being brought to the stator coils of a goniometer placed at the centre of the whole system. The entire area covered is only a matter of twenty feet square—a great deal less than that required for medium-wave direction-finding. An Empire MaU Inauguration WHEN a member of the top table of any gastronomic con course of people is overheard to say that a very distin guished gathering is present, then surely few can deny it. Such a remark was overheard on June 29 at a notable function, when some 250 guests of His Majesty's Government visited Southampton to witness the inauguration of the first stage of the Empire Air Mail scheme, whereby all letters and postcards are sent to East and South Africa by air. The guests embarked at Southampton and made the journey down to Hythe on board the MA'. Medina. Riding between the special rafts of Hythe Pier was the good ship Centurion, with its commander, Captain F. ). Bailey, waiting to receive letters from H.M. the King. After brief speeches by the Rt. Hon. Viscount Swinton, G.B.E., M.C., Major the Rt. Hon. G. C. Tryon, M.P., Senator the Hon C. F. Clarkson and Sir J. George Beharrell, D.S.O.. the Royal letters were stamped, placed in a silk bag and sealed by a postman prior to handing over to Captain Bailey, who forthwith went aboard the Cen turion. A slight hitch occurred with the starting of No. 1 port motor, but after a not unpleasant delay of thirty minutes Centurion took off and duly circled the M.V. Medina. During the passage out from Berth 46, sixteen different Power boats raced past the Medina at intervals—so that her passengers could learn something of the wide range of these craft A number of them are now over in the Shannon. Back at Southampton the partv was entertained to a lun cheon presided over by Viscount Swinton—at the conclusion of which it was announced that the Centurion had radioed her position as approaching Marseilles.
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