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Aviation History
1935
1935 - 0566.PDF
278 FLIGHT. MARCH 14, To,35_ Two Standard Radio equip- j ments. At the top, on the j left, is the ATR.6, for j medium- and short-wave j work on large aircraft ; the j receiver is shown below it. • On the right is the ATR.3, j with its receiver unit, in- j tended for short-wave work I in fighting machines. no mechanical controls are employed, and all backlash is thereby obviated. For the reception of CAY. telegraphy, a local oscillation provides the required beat note, maintained at constant amplitude by the automatic volume control, with the result that the aircraft may fly directly over a station transmitting C.W telegraphy without loss of beat note, and without in terference due to key clicks. Both the transmitter and receiver are provided with metal bosses carrying flexible rubber rings which are held in special supports inside a welded tubular steel crate; this crate is enclosed by ventilated detachable sides. Thus both the trans mitter and receiver are contained in one unit, floating on rubber, and the crate can be bolted direct into the aircraft without any special trouble. For small aircraft, the trans mitter and receiver can bs supplied in separate crates. The control unit is particularly interesting, and can be fitted near the pilot when the installation is remotely con trolled. It contains a D.C. feed meter indicating the total current consumption, an aerial ammeter indicating the aerial current, three jacks for microphone, telephones and key, and a special receiver, tuning control with wave-change switch where the receiver employs two wavebands. It is connected to the installation by a cable carried in a braided. sleeve to prevent interference from external sources being picked up on the receiver. Its construction is similar, to that of the main installation, except that it is not contained inside a crate, and the supports for the rubber rings are fitted directly to the structure of the aircraft. Five levers provide remote controls through Bowden-type wires for " ofl-receive-send" switch, " C.W.-I.C.W." transmitter, " C.W-I.CAV." receiver, and wavelength change for transmitter. A trailing aerial is normally used, but in large aircraft a fixed aerial may be found sufficient. Power supply is from a dual-voltage wind- or engine-driven generator, although, if required, a rotary transformer can be arranged to run from the aircraft lighting battery. Including generator and aerial equipment, the approximate total weight of the A.C.44 is 6olb:, while the dimensions of the crate carrying the receiver and transmitter are gin. x i6|in. x 17m , and of the control unit 8]in. xdiin.x 2|in. Another Plessey equipment, the AC.57, is designed to pro vide telephonic or telegraphic communication en short wave lengths from fixed aerial systems on high-speed military machines. As in the A-C44, the entire equipment, with the exception of the controls, is carried in a steel crate. The wavelength range of the transmitter is 65 to 120 metres or 40 to 80 metres, the output power to the aerial being 15 . • :. • ' . :- "•'£; .-. watts. A special valve made under Plessey patents enables a very small and compact transmitter to be built, incorporat ing a master oscillator circuit having all the frequency stability of a larger transmitter employing a separate master oscillator. Anode modulation providing a depth of 70 per cent, for tele phony and I.C.W. telegraphy is employed on the amplifier. The tuning controls have locking devices so that they can be set at any two wavelengths in the selected band. Operating either from 70 to 450 metres, or from 40 to 120 metres, the receiving circuit is a six-valve superheterodyne with a H.F. amplifier preceding the frequency-changing valve. Automatic volume control is employed, control of the beat note for C.W. reception being maintained as in the A.C.44: The tuning control is also electrically operated, as in tntr t-ype of installation already described. The weight of the installation is approximately 4olb., and the dimensions of the complete crate 8£in x ijjin. x 7|m. A Wide Range There are seven different sets of aircraft radio equipment listed by Standard Telephones and Cables, Ltd. Tins com pany operates its own aeroplane for experimental work, audi has been able to correlate the research work of its laboratories and that in the air, with good results. The company's ATR.2 set is tor transmission and recepuo of telephony, CAV. and M.CAV. (modulated continuous wave) telegraphy on medium and short wavelengths, and it is • fore appropriate for medium- and large-sized aircraft carry 0 an operator. The transmitter is virtually divided into units, one covering the 550-1,100 metre waveband, an other in two-to-one wavelength range chosen between 30 ^ r20 metres, as, for example, 40-80 metres. The receiver 1 contained, and covers both wavebands without change 0 ^ The normal supply is from a dual-voltage air-driven get1 ^ without accumulators or dry batteries. If required, no ' a rotary converter - -^" ""• accuffla,a system can be supplied with accumu^' switchbox and charging generator, so that the eclUIP™ aiYC be used on the ground. The transmitter circuit is a flv - ^ one, including a master oscillator to ensure stabiiiy- output power is 20 watts on telephony or telegraphy ^^j. The receiver for medium-wave reception has one stage For grid II.F. stage followed by a detector and L.i "7Rector short-wave reception an oscillator valve" and the tirs ^ .^ precede the above valves, thereby converting the c 0CI1,i a five-valve superheterodvne. The medium-wave air" °0j-0 range is from 120 to 150 miles for telephony, and 5 ^ g$. for C.W. telegraphy. The ground-to-air range iron ^ ^ class aerodrome equipment should be about 15° m phony, and 300 miles for C.W. telegraphy.
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