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Aviation History
1949
1949 - 0729.PDF
(Left) Pictorial representation of Standard Telephones cathode-ray V.H.F. D;F. installation at an airport, showing the main station with the remote ind;cato«-"frr-tfefsjtower. (Right) The nt*LMarconi caikode- ray V.H.F. DjF.NquijHMiil'" with (above) the aerial head carrying an H array of folded dipoles, a magslip and goniometer. AIR RADIO to the other, but in the main they will hold good. Airfield and Approach Control.—Communication between the control tower and aircraft in the air is probably the first essential communication service of an airport, and this is now achieved almost universally by V.H.F. radio telephone. H.F. and M.F. are still used, however, and are likely to continue for several years yet. In the United Kingdom, the airfield control-zone is usually taken as an area of five miles' radius from the control tower, whereas the approach zone may be anything from five to fifty miles. In other parts of the world these distances may be greatly exceeded. In some cases the approach and airfield control areas become one and the same. Generally speaking, the power output of V.H.F. transmitters for airfield control should be from 5 to 25 watts and for approach control from 50 to 100 watts. A number of V.H.F. radio equipments are in production to-day, most of the low-power sets being made in the com- bined form of transmitter/receiver. Since several channels are normally in use at an airport, it is more convenient for the transmitters and receivers to be separate units, and most manufacturers have made suitable modifications to separate the transmitters and receivers. Such sets are manufactured in this country by the General Electric Co.. Ltd., Marconi's Wireless Telegraph Co., Ltd., and Pye Telecommunications, Ltd. All these small transmitters have an output of be- tween 10 and 15 watts and, in the case of the Marconi transmitter, M.C.W. at 1,000 cycles is also available where thi" service is required. E. K. Cole, Ltd., make a small transmitter with an output of 5 watts. The above manu- facturers also produce suitable receivers, and a model made by E. K. Cole, Ltd., for the Services, the R.1392 receiver, is in use at most of the larger airports in the country. Most of these new receivers incorporate a muting system which completely quietens the loudspeaker during no-signal periods. E. K. Cole, Ltd., have under development a new "miniaturized" receiver occupying only 7m space on a standard international rack. The receiver will incorporate effective muting, a noise-suppressor, and a channel indi- cator. Apart from working with aircraft, the control tower of a large airfield may also wish to communicate with fire tenders, ambulances, etc., on the airfield, and in this con- nection experiments have recently been taking place at London Airport and a fitting programme has been started. Mobile versions of the above small transmitters and re- ceivers are in very many cases suitable for such purposes. Larger V.H.F. transmitters for approach control are also available from most manufacturers, including Pye Tele- communications, Ltd. (100 W), Standard Telephones and Cables, Ltd. (50 W), Marconi's Wireless Telegraph Co., Ltd. (50 W), Redifiusion, Ltd. (50 W), The General Elec- tric Co., Ltd. (100 W), Murphy Radio, Ltd. (50 W). A typical example of such transmitters is the Standard Tele- phones V.H.F. Transmitter Type DU2, brief details of which are: Frequency range .. 115-135 mc/s Service M.C.W. and telephonyPower output .... 45-55 watts Frequency control. . CrystalNo. of channels .. Two Supply 110/250 V, 50/60 eye, single phasePower consumption Not exceeding 1 kW The transmitter incorporates an automatic system of modu- lation-depth control. Where H.F. communications (2-8 mc/s) are required for short-range radio telephony, there are a few transmitters and receivers available. G.E.C. manufacture a crystal- controlled receiver, and Rediffusion have a transmitter/ receiver, in one cabinet, with which it is possible to select instantly any one of five pre-set frequencies. Murphy have recently produced a prototype single-channel H.F. re- ceiver specially developed for reception of H.F. radio tele- phony on airfields. Mention should also be made of the receiver manufactured by the Decca Navigator Co., Ltd., which is suitable for this purpose and is referred to in more detail in a later paragraph. Communication receivers manufactured by most of the larger firms may be used for reception of radio telephony in the H.F. band, but the crystal-controlled receiver is to-be preferred as it has the property of always being correctly tuned. The Rediffusion transmitter/receiver Type GR49 has been used at many airfields; the abridged specification is as follows: — Frequency range .. 1.4 to 8 mc/s Service Telephony No. of channels .. Five (pre-set) Frequency control.. Crystal R.F. power output. 50 W An alternative edition to this set incorporates C.W. facilities. There are a number of accessories which are bound to form part of the complete tower communication system, one of the most necessary being recorders suitable for making a permanent record of the incoming and outgoing conversa- tions between the tower and aircraft. These are being made in one form or another by The Dictaphone Co., Ltd.,
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