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Aviation History
1935
1935 - 0562.PDF
2/0 LIGHT. MARCH 14, To,. reduced power for medium-size machines. It provides f0 graphy by C.W. (continuous wave) and I.C.W Interrupted The wireless cabin of an Imperial Airways H.P.42, showing the Marconi Type A.D. 41/42 equipment, with homing device (at top). The aerial winch can be seen by the door leading to the pilots' compartment. running his generator or transmit a certain note. Lympne, Pulham and Croydon then all take bearings on these signals. These bearings are transmitted to the control tower at Croydon, where they are laid off on a map, and the position at which they cut is then indicated to the pilot of the aircraft. Should this full organisation for some reason not be working, the pilot can obtain a bearing from any one of the three stations. This system of control has the advantage that it does not necessitate carrying any equipment in the aircraft except that used for radio communication. Another form of direction-finding apparatus is the homing device, whereby an aircraft itself can be flown direct towards any station which is sending out radio transmissions. A reading of the compass then gives the pilot the bearing of that station. This is of particular value where there are no regular ground direction-finding stations. A development of this system is now in the course of evolution. This makes use of a rotatable loop aerial, and thereby obviates slewing the aircraft itself: in some cases the reading is shown on a dial, which gives a bearing relative to the aircraft's head. The final form of navigational aid described in the fol lowing notes is the visual or audible beacon. This is in two forms, one for use on air routes and one for landing. The former necessitates the aircraft carrying a special small receiver by means of which the pilot can tell whether or not he is flying directly along a radio-beacon trans mission. This has been widely used in America, but in England, where it is vitally necessary for a control officer to keep track of every single aircraft, the cross-bearing system from the ground direction-finding stations is generally considered to be more applicable to the circum stances. Now to deal *ith actual equipment. An interesting example is the Marconi A D. 41/42, shown above. Two editions of this type are available, one of full power lor use on large civil, military and naval aircraft, and one of continuous wave), and telephony, both the transmitter receiver being designed to cover a wavelength band of 1,000 metres. s°° t(1 The transmitter incorporates two power magnifiers "drive" stage and one modulator. The power rating ie watts to the anodes of the magnifier valves on C.W. teWra'if at full power, and 100 watts on reduced power. The dial of the variable condenser controlling the drive ' cuit is calibrated in metres, permitting the rapid adiustm "t of the transmitter to any desired wavelength within the li v of the set. The method of modulation is by direct-current grid control so that the modulation valve acts as a variable leak aero 1 the grid circuit of the magnifier valve, ensuring full (jel modulation. - p Various Range Under good conditions the air-to-ground range for telephony is 250 miles on full power, and 200 miles on reduced power for I.C.W. telegraphy it is 300 miles and 250 miles; and for C.W. telegraphy 500 miles and 375 miles. The receiver is continuously adjustable over the same wave band as the transmitter, . and makes use of one screened-grid H.F. amplifier, one detector with reaction coupling, and one pentode output. Power supply is normally derived from a wind-driven generator providing both high- and low-tension outputs. Remote control of both transmitter and receiver and the tuning adjustment are arranged through Bowden-type cables. Intercommunication apparatus can be supplied, and enables either the pilot or an operator to use the set, and also affords a means of communication between them. For normal use over iong ranges a trailing aerial is fitted. The weight of the transmitter is 251b. 40Z. and of the receiver nib. 140Z. The dimensions of the former are isin. by i4jin. by 8Jin., and of the latter 7m. by 145m. by 8Jin. Another set, designed for military machines ot the lighter class, is the Marconi A.D. 43/44. It gives communication by telegraphy on C.W. and I.C.W. and by telephony over a wave-range band of 50 to 100 metres. The transmitter incor porates a pentode valve used as a combined master oscillator and magnifier, and a second pentode valve used as a combined Marconi short-wave equipment Type A.D. 43,44 fttefi fighter. Note the welded-ammiriium-tube cradle, which the set is suspended by rubber cords. modulator and sub-modulator. The tuning control 0! the Pa** master oscillator circuit is calibrated directly in metre . (? rating of the transmitter is up to 20 watts, approxih the anode of the magnifier valve. The receiver is a six-valve superheterodyne. 0(,taio'» Under average conditions it should be possible to . j^v range of 60, 50, and 38 miles for C.W., I.C.W.. ana ^ ¥ respectively, while for inter-aircraft work these rang approximately nineteen, twelve, and nine. nvprox^1' With dual generator and remote control the W.^&e* weight of the complete equipment is 651b., while ^ tt)f t of the transmitter are Mrs'"- by 15m by 6|, an ceiver 7ffin. by I5in. by 6 j.
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