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Aviation History
1949
1949 - 0730.PDF
April 28th, 1949 485 Boosey and Hawkes, Ltd., Electric and Musical Industries, Ltd., and Simon Sound Services. An inter-communication telephone system is usually part of the controller's equipment so that he may have imme- diate call on the meteorological office, fire tenders, crash crews, etc. The simplest type has ten keys, the depression of any one instantly calling the desired department. Suit- able installations may be obtained from the Automatic Tele- phone Electric Co., Ltd., Standard Telephones and Cables, Ltd., Inter-Office Telephones, Ltd., the Modem Telephone Co., Ltd., and the Telephone Manufacturing Co., Ltd. Another accessory which should prove valuable in the future is the constant-output microphone amplifier, one of which is shortly to be produced by A. C. Cossor, Ltd. Such a device enables constant modulation level to be radiated by the transmitter irrespective of the distance of the micro- phone from the controller. It should be mentioned that some transmitters already incorporate this feature. Complete systems for airport-tower installations are manufactured by Marconi, S.T.C., and G.E.C. Inter- national Aeradio, Ltd., act as consultants in this important sphere of airport installations. Area Control and Point-to-Point Communication.—For this service it is usual to find the higher-powered transmit- ters, ranging from 300 W up to 50 kW. Most transmitters now manufactured are provided with optional crystal or high-stability master oscillators, which feature has recently become more important due to the stricter radio frequency regulations made at Atlantic City in 1947. Transmitters of all sizes are manufactured by S.T.C., Marconi and Re- diffusion. The G.E.C. make a twin-channel 150 W trans- mitter as well as a single-channel 1 kW model, and the Cossor Radar transmitter, Type T 1509, is much in use by the Services and civil aviation authorities. Particular men- tion should be made of the new S.T.C. transmitter Type DS10, which provides for a number of different radio fre- quencies using a common power pack, the whole being assembled in an attractive cabinet. Suitable communication receivers are those by Marconi, who manufacture several different models, S.T.C., Redif- fusion, G.E.C. and Stratton and Co., Ltd. Some receivers incorporate the additional feature of a crystal guard- channel, a practice which it is hoped will be followed by other manufacturers in the near future. Single-channel crystal-controlled receivers are available from G.E.C. and Decca Navigator. The latter company are shortly to pro- duce their Type 160 receiver, which incorporates many new features. Apart from the fact that the receiver may be controlled by a crystal or optional master-oscillator, there is provision for remote control of the B.F.O. and audio gain up to a distance of 100 yards without R.F. or A.F. on the control lines. Mention should also be made of recent developments in regard to frequency-shift telegraphy and radio teleprinter equipment. For heavily loaded point-to-point circuits there is much to be gained by use of radio teleprinters, and a further development may be their use in aircraft. Apart from the fact that teleprinter working has an added degree of secrecy, it is easier to train the operators, and, in emer- gency, any unskilled person is able to transmit a message. Recent investigations have shown that the best and most reliable results can be obtained by '' frequency shift'' working, and suitable equipments for this service are manu- factured by Marconi, S.T.C., Rediffusion and British Tele- communications Research, Ltd. Such equipments can be arranged for use in dual-or triple-diversity' reception. The frequency-shift receiving adapter as manufactured by British Telecommunications Research, Ltd., is probably the most compact unit made to-day. Occasionally there is a necessity for short-distance radio teleprinter working, for instance between airport and city centre. This may be done by using any of the small V.H.F. transmitters and receivers mentioned above, with suitable tone generators and detectors in the transmitting and receiving ends respectively. Such adaptors may be obtained from most manufacturers of carrier telegraph and telephone equipment such as the G.E.C., S.T.C., Siemens Bros., Ltd., and the Telephone Manufacturing Co., Ltd. Navigational Aids M.F. beacons, although one of the original radio aids to navigation, are still one of the most popular with air crews. The ground equipment consists of a simple transmitter to- gether with a non-directional aerial, an identity call-sign being given out automatically in morse code. In the past most beacons had an output power in the region of 200- 500 watts and, whilst these have proved satisfactory in temperate climates, there are good reasons for higher power, say. about 2 kW, in sub-tropical and tropical climates, due to the higher atmospheric noise level. Transmitters for this purpose are made by the companies referred to above under area and point-to-point working. Metropolitan Vickers make a small 100-watt transmitter which can be used as a locator beacon. Direction-finding Service.—This is still in great demand in civil aviation on M.F., HF. and V.H.F. Direction- finding Stations of the M.F. type are not used so much nowadays but are still manufactured by Marconi. H.F. direction-finding is used to some extent on the long-distance air routes, and a recent additional feature of this type of station is cathode-ray presentation. The latest type of equipment as manufactured by both Marconi and S.T.C. incorporate this feature. V.H.F. D/F. is becoming more widely used, particularly as it is well suited for the homing of aircraft to the airfield. A simple- but effective type of .equipment for manual operation is manufactured by E. K. (Right) A general-purpose six-channel 500-wott trans- Type T6S57I by j^ Remote control up !ral miles is possible. (Left) The transm/ttarTTSJS* manufactured by ^Offflf • ' suitable for medium distance air/ground and point-to-point working.
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