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Aviation History
1947
1947 - 1921.PDF
NOVEMBER 6TH, 1947 FLIGHT A New British Radio Compass Standardized for the R.A.F. and Available for Civil Aircraft MENTION of the new G.E.C. Radio Compass wasmade in our review of the S.B.A.C. Exhibitionat Radlett but, since this device is the first of its kind to be wholly designed and manufactured in %iis country, it merits a fuller description, particularly since it is to become standard equipment for the Royal Air Force. Developed by the Salford Electrical Instruments, Ltd., division of G.E.C. in conjunction with the R.A.E., Farnborough, the compass, when shown at Radlett and Radiolympia, excited considerable attention. In par- ticular, the major airline companies evinced a great deal of interest, and there is every intention on the part of the manufacturers to make the equipment avail- able, possibly in a modified form, to commercial users. The name '' Radio Compass '' implies the function of the equipment. Receiver, aerials and circuits combine to produce on a 360-degree dial an indication of the bearing of the station or beacon being received. Thus it is possible to home, to obtain fixes, or to obtain bearings at regular intervals for normal D.R. naviga- tion. Physically, the equipment comprises a receiver, a loop aerial, sense aerial, and twin control units (one each for navigator and pilot), together with a large, clear "compass" dial for the navigator, and a smaller repeater for the pilot. So many refinements are incorporated in these essen- tial units that only the more striking items can be de- tailed. Beginning, appropriately, with the loop aerial, this now belies its name, for it has been reduced to a flat lozenge-shaped coil only a few inches in depth, with iron-dust cores. For retrospective fitting to aircraft this loop is enclosed in a housing shaped rather like a flat-fish ; the aerodynamic drag of this housing is of the order of one-third that of the previously used stan- Units making up a com- plete aircraft installation. They comprise, left to right, first control box, junction box, navigator's large - diameter bearing indicator, the flat aerial wit with motorised drive, and, below it, the cathode follower unit, second con- trol box, pilot's repeater indicator, and receiver unit. Receiver unit with cover removed to show the neat interior arrangement. 7 he rotary transformer can be seen at the rear. dard loin loop. For incorporation in new aircraft a "dish-pan" type of housing is used, and the loop aerial is accommodated inside the aircraft skin so that there is no external projection. Automatic Direction Finding • \, In the design of the receiver, which covers the fre- quency-range of beacons and broadcasting stations, ease of servicing has been the guiding line. Unit con- struction has been carried to the stage in which the whole equipment can be dissembled into ten units, in- cluding controls, amplifiers, wavechange and condenser drive, generator and filter unit, etc. Twenty-one valves are employed, all of approved type and easily replace- able, with filaments supplied directly from the aircraft D.C. supply voltage. The main control switch on the control panel gives the normal facilities of a receivei with either automatic or manual volume control, to- gether with automatic direction finding ("A.D.F.") and a position marked as "LOOP." Use of the receiver in the ordinary way requires no specific comment, but reference should be made to the ingenious arrangements for tuning. When the receiver is switched on, an optically enlarged frequency scale is projected with considerable brilliance on to the kidney- shaped ground-glass screens of each of the control boxes. Motor-driven tuning is employed, and it is "necessary only to turn the tuning knob slightly to left or right to decrease or increase frequency. The servo drive is of proportional type whereby the speed of tuning is dependent upon the amount by which the knob has been turned. Nothing has been sacrificed for compactness in the control panel, and facility in the operation of this type of tuning control is claimed to be very rapidly acquired. . - When the required broadcast station or beacon has been tuned-in (and in this connection it should be stressed that a special ground station is not required, any suitable beacon broadcasting station can be used) a bearing may be obtained bv switching the main control to '' LOOP '' and operating another similar servo control for driving the loop until the null position has been found aurally. A check for sense is made in the usual way by shifting
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