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Aviation History
1934
1934 - 0306.PDF
FLIGHT, MARCH 29, 1934 PLESSEY AIRCRAFT RADIO EQUIPMENT ALREADY there are a large number of the smaller—small that is in comparison with Imperial Air-ways—operators who have found the use of radioa very great advantage. Not only is this the. case lor those taxi operators who, particularly when on newspaper and Press work, have to fly through almost every kind of weather and can only do so by keeping in radio touch with Croydon, but also there is no doubt that it will be impossible to run the majority of the proposed internal air lines, about which everyone is talking so much now, without the widespread use of radio. It will be necessary to have a regular and efficient meteorological service for the dissemination of weather reports and also a number of direction finding stations which can give pilots of those aircraft accurate information as to their position, at any moment during the flight. A firm which has recently evolved a compact light, but none the less efficient radio equipment for aircraft in this category, is the Plessey Co., of Ilford. We recently had the opportunity of trying out their AC44 equipment as fitted in a " Moth," and found it not only simple, but as far as we could discover foolproof to work. We had been told that safety devices made it impossible to over- load the valves, and these were tested by earthing the aerial and then switching on the transmitter. No harm whatsoever resulted. This equipment is made in two forms. The A.C.44, which is of medium power and is intended for use on civil or military aircraft where telegraph or telephone communication is required on medium waves and where remote operation and wave length changing is required between any one of four preset wave lengths ; and the A.C.44B., which is similar in its essentials, but provides for a continuously variable wave length range and is not intended for installations which necessitate the use of re- mote control. The A.C.44 can be preset to operate on four wave lengths between 600 and 1 000 metres, and those generally used for aircraft purposes are 600, 862, 900 and 930 metres. If desired, however, other wave bands can be provided. The receiver tuning is continuously variable over the same wave band and, if required, can be provided with a second band above or below the normal or on short waves. The transmitter, which is of the type employing a master oscillator for frequency control, is coupled to the aerial circuit in a special manner which prevents overloading of the amplifiers should the aerial be lost. Telegraphy and I.C.W. are obtained by means of a low power modulation system. The output of the transmitter is: — C.W. telegraphy .. Telephone I.C.W. telegraphy 36 watts 18 ,, 18 ,, Under normal conditions a range of 150 miles is obtained with telegraphy and I.C.W. and 250 miles with C.W. The construction is somewhat unique in that external shock absorbing devices are not required, as the apparatus is carried on a magnesium framework which, through sorbo rubber rings, is connected to a tubular steel crate with enclosed ventilated sides. The receiver is of the super- heterodyne type with automatic volume control, and special circuits for the reception of C.W. telegraphic signals. Four valves are employed with an output power sufficient for loud reception in two pairs of headphones. The control unit of the Plessey equipment is an unusual but efficient item, which solves all the problems connected with remote control. It contains small meters showing the total current consumption and the aerial current, jacks for microphone telephones and key, a volume control, and a receiver tuning control, thus obviating the necessity for operating a tuning control on the main instrument by mechanical means with its attendant drawbacks. The use of a tuning control separated from the receiver by many feet of cable is a great achievement, as it would normally, one would suppose, lead to instability. This drawback has, however, been completely overcome in this Plessey equipment. This method of separating the control unit from the main instrument confines the use of Bowden wire controls to the operation of definite-movement items like the off-receive-send switch, C.W.-telephone-I.C.W. switches for transmitter and receiver and the wave length change. Either a trailing aerial or a fixed aerial may be used and any normal form of power supply such as a double voltage wind or engine-driven generator (the model we inspected was supplied by a double voltage generator made by the Electrode-Dynamic Co.), or a rotary transformer running from a battery, according to which suits the aircraft best. The following table gives the dimensions and weight of the equipment: — Dimensions 14 x 7 x 11 in. 14 x 7 x 3J in. 8f x 6| x 2£ in. TransmitterReceiver Control unitRemote controls Winch with aerial wire and weightFairlead Microphone Telephones (one pair) Telegraph key Generator and wind- mill Cables 6 in. diam. According to in-stallation 12 x 4£ in. According to in-stallation 9 x 16| x 17 in. Weight15 lb. 3 lb. 11 oz.3 lb. 2 oz. 6 1b. 7 1b. CrateApproximate total weight, type A.C. 44 „ A.C. 44B 2 lb. 8 oz. 10 oz. 10 oz. 12 oz. 14 lb. 5 1b.60 lb. 54 1b. The Plessey AC.44 aircraft radio equipment. The control unit is on the left. From this it will be seen that the whole outfit is very compact and, indeed, still allows ample room for the passenger when installed in the front cockpit of a Moth." Television developments BEFORE a number of Air Ministry officials, a demon- stration of Baird Television was given on Monday, March 26. The latest apparatus is a great improvement on that previously used. The definition has been made far finer than hitherto by increasing the screen division to 180, horizontally. This has largely eradicated flicker, and the picture, as presented on the fluorescent screen, can be compared in quality to the best newspaper photograph reproduction. The cathode ray tube has also been im- proved and enlarged, so that the screen for normal home use is now about 10 by 12 inches in size. It was suggested, at the demonstration, that control stations at aerodromes could in future televise a map to aircraft pilots whereon would be marked their position as obtained from directional wireless fixes. The position of other aircraft in the vicinity would also be marked, and it was thereby con- sidered that flight through fog would be made safer. Prob- ably, however, the weight of the apparatus will be con- sidered too much for the present, and it does not seem likely that much use will be made of the system in aircraft until a means is discovered of showing the pilot a picture of the ground and obstructions ahead of, and immediately in the vicinity of, his machine. 306
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