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Aviation History
1958
1958 - 0658.PDF
674 FLIGHT, 16 May 1958 Display of the Raytheon A.T.C. radar. Map details are electronically superimposed, together with M.T.I, ami circular polarization. AIR TRAFFIC CONTROL... U.S.A.F.; one at Eglin A.F.B., Florida, and another for laterinstallation at Wright-Patterson A.F.B., Ohio. A runner-up for the AMB contract was the system proposed byInternational Business Machines Corporation, called Automatic Position Telemetering. This, it is claimed, can be integrated withautomatic data processing machines and has the advantage of low airborne weight. A.P.T. operates by measuring the time of arrivalof four coded pulses of U.H.F. energy at four ground receiving sites located about 20 miles apart. Pulses sent from aircraft arereceived in a co-ordinate conversion computer to plot the aircraft's location; altitude data could be added by additional pulses. Theaccuracy predicted is 0.05 miles within the station network and 1.5 miles at 90 miles range. Whatever the prospects for computer methods of easing thetask of the air traffic controller, current systems rely heavily on surveillance, airfield and precision approach radars. Presentwork in this direction is directed particularly towards extending en route radar coverage. The very extensive programmes intro-duced in the U.S.A. and Canada for coast-to-coast coverage are examples in point and the big 40ft Raytheon L-band antennae arespreading in a vast (and highly expensive) network across North America. Radars in use for air traffic control purposes may be roughlysubdivided by wavelengths. It is generally true to say that the choice of wavelength is made by consideration of the range, thepulse power required and the necessity to avoid clutter from per- manent echoes, rain and cloud. Interference is reduced by the useof longer wavelengths (it increases rapidly between the usual microwave bands of 25cm through 10cm to 3cm) but resolvingpower and the possibility of gapless cover fall off. For close delineation, such as is required for airfield surface movementindicators (A.S.M.I.) wavelengths of 3cm are usual. London Air port's Decca A.S.M.I. is an 8mm band radar, which will dis-tinguish the lights along the Bath road or, as on one occasion, a lone policeman lost and wandering in the fog. For convenience, each band is represented by an alphabeticalsymbol; thus the Q-band is 8mm, the X-band is 3cm, and so on up to the usual maximum in use of 50cm (L-band). For radars of23cm or less, circular polarization to reduce rain interference is regarded as essential.Another technique, moving target indication (M.T.I.) has been adopted to suppress permanent echoes. Long-wavelength radarswith M.T.I. give a performance in clutter conditions superior to their shorter wavelength counterparts. Advancing knowledge in radar design is making possibleimproved en route surveillance radar, new and better methods of radar siting combined with centralized presentation and firststeps towards the analysis of flight progress by digital computa- tion. The M.T.C.A. has recently issued a draft specification fora surveillance radar that will provide a radius of cover of 85 n.m. over 5,000ft; three such radars could give coverage over most of theU.K. F.LR.s. Microwave links, such as that by Marconi, would bring the P.P.I. displays directly into control centres distant fromthe aerials. The Marconi SX.101 radar link will relay one, two or three radar presentations over hundreds of miles, if necessary, sothat a complete picture from several radars may be concentrated in one centre. Height finding radars have a greater use in determining aircraftvertical separations than they do in determining absolute height (where their accuracy may be in doubt) but they serve a useful purpose where the controller is not in communication with theaircraft displayed on his scope or an altimeter failure has occurred. The general use of transponders for a secondary radar surveillancesystem still appears to be some way off. Although the advantages are well-known, general agreement on specifications must bereached and installation completed. America's Airways Moderniza- tion Board has evaluated 12 Eastern Air Lines flights equippedwith Wilcox Electric Co. transponders; and equipment for using beacon information is now operating at Idlewild, Newark and LaGuardia A.T.C. towers. Other firms offering transponders are A. C. Cossor, Collins Radio, F.T1., Radio Corporation of Americaand the Stewart-Warner Corporation. A considerable number of manufacturers are engaged in theproduction of radars in Europe and North America and it is not possible to list them all. Brief mention should be given, however,to Marconi's 10cm (S-band) SR.1000 radar transmitter/receiver which has been designed for long-range cover. Features claimedfor it are novel construction to give easy maintenance, compact packaging and a built-in monitoring system. An L-band apparatusby the same manufacturer is the type SR.1030. Marconi offer in addition a range of 25 cm and 50 cm surveillance radars, airfieldcontrol radars and height finding equipment. They hope to offer soon data handling equipment designed to accept information fromradar sources via a tracking group as well as from teleprinter links and R.T. channels and to display it on bright cathode ray tubes inthe form of an up-to-date P.P.I, showing identification letters and heights. The system will have a storage capacity of up to 160tracks available for onward transmission to adjacent A.T.C. centres by data links, and for input to a computer. A system on theselines was shown at RJR..E., Malvern, and described in Flight for May 2. The Cossor Radio company have developed in addition to theircompact high power CR.21 10 cm surveillance radar with M.T.I. and circular polarization, the CRD.23, "a new display systemwhich anticipates the air traffic problem for several years to come." The system exploits the unused time between successive radarscans to present up to ten identification numerals against target echoes. A range and bearing marker may also be positioned any-where on the display and rotated to give the bearing and range between any two points. Any number of displays may be usedand located up to two miles or more from the aerial, and the centre of rotation of a display can be off-set up to 60 nan. Arrangementsare incorporated so that a particular echo can be passed over to a controller covering an adjacent section without breaking continuityof plotting. Facilities are offered for video mapping and for pre- senting CRDF information injected into the P.P.I, display. Developments in France include an S-band (10 cm) radar manu-factured by the Societe Nouvelle de rOutillage R.B.V. et de la Radio-Industrie. It is being used in Brussels over the period ofInternational Exhibition by Regie de Voies Aeriennes Beiges. The equipment is designed to plot simultaneously the three spaceco-ordinates of any number of targets; the height-finding feature is claimed to be very accurate—a tolerance of 700ft at 100 n.m. isgiven. Air traffic control presents such a variety of bewildering andurgent problems that it is hardly surprising that international regulation lags behind advancing technology. New equipment isbeing applied to solve the demands for closer separations, unhampered climb-outs and let-downs of jet aircraft and aboveall, relief of the heavy workload of pilot and controller alike. The early promise of radar is being fulfilled with the advanced equip-ment now coming into service but the problem of obtaining, trans- mitting, handling and storing data remains. Some of the methodsproposed for handling data are reviewed in this article; how they will be used in practice will depend upon the results of pro-tracted evaluations. Suitability can fairly easily be determined; to achieve the standard of reliability required will be a long andpainstaking task. ATP Cossor CRJ1 in a caravan. The quarter-wave plate is raised in front of the aeriql horn to produce circular polarization.
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