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Aviation History
1956
1956 - 1359.PDF
FLIGHT, 21 September 1956 511 New Developments in Radio and Radar A User's Commentary on Ground and Airborne Equipment at Farnborough At this year's S.B.A.C. Show the Marconi company relayed displays, by a new microwave link, from their 5.232 radar at London Airport. The mobile link receiver is seen here on site at farnborough. THE radio industry always produces its crop of interestingexhibits at the S.B.A.C. show and this year ran true to form.In fact it is clear that the radio side of the aeronautical industry is as conscious of the early September deadline as is theaircraft manufacturer himself. Farnborough has no rival any- where as a unique assembly point for anyone connected with theair transport business and the ground services needed to support it throughout the world. So, for the airline operators and thosewho have responsibilities for the provision and operation of air and ground radio services, the array of equipments for all aviationradio purposes was as complete as it could possibly be. Some of the more important advances were to be found amongstthe ground scanning radars and there was much evidence that the art has moved a long way from the "raw radar" stage. Generallyspeaking, ground radars made rather slow progress in their adop- tion as important surveillance tools of the controllers in the busyair-traffic complexes. This was partly due to the view widely held for a number of years that all that was needed was a highlyprecise radio navigation system and its attendant communications. Over the years this outlook has undergone a good deal of change;the navigation system and its associated communications are s ill a "must," but the third principal partner in areas of high trafficdensity is ground radar. At least part of the trouble has been that the raw radar gavetoo much of the kind of information the ground operator did not want as an inescapable accompaniment to the information he didwant. His interpretation of what is basically a very simple presentation was very seriously marred by the clutter of thepermanent echo pattern and returns, in greater or lesser degree, from areas of precipitation. Both features of the radar techniquecan, of course, be made use of in particular applications such as the A.S.M.I or the cloud-mapping radar, but in the surveillanceradar for air control purposes they confront the operator with so much redundant information. Further, the operation of a groundradar can be much simplified if the facility exists to transfer to the display certain other information external to the radar path, andalso to extract information from it of a quantitative kind about the movement of aircraft in relation to each other and to fixed pointsin the control pattern. The radars demonstrated at Farnborough this year showed very considerable developments along theselines. Four manufacturers showed substantial developments inground radars for specific applications in air traffic control and some account of these will show the progress which has beenmade. A.C. Cossor exhibited their new airfield control radar, asurveillance equipment which is designated "Cossor Radar Type 21" and operates at 10 cm wavelength with 500 kW peakpower and a 1 microsecond pulse. It is derived from the A.C.R.6, to which it has a generally similar performance and coveragediagram. It was presented as a twin-channel equipment in mobile form with two table-top type displays in the vehicleitself, and a third remoted for external demonstration. The major noteworthy features of the C.R.21 are the movingtarget-indicator system and the anti-rain quarter-wave pla'e arrangements. The M.T.I, unit uses the established coho-stalotechnique. In the demonstration the utility and stability of this feature were evident. The sub-clutter visibility of this particularequipment was said to be of the order of 23 dB, which in opera- tional terms appears to mean that the permanent echoes can beeffectively eliminated without noticeable loss of performance or coverage on aircraft.The quarter-wave plate used in this equipment has been mounted externally to the horn feed on the scanner and itsposition is remotely controlled so that the rain clouds may be either seen or eliminated at the discretion of the radar operator.A discrimination of some 20 dB in favour of the aircraft against rain is being achieved. Whatever it did to the flying, this Farn-borough week played up to the radar exhibitors by providing an admirable opportunity to demonstrate the need for anti-rainprovisions in search radar, and the demonstration was very. effective. The advantage of putting the quarter-wave plate outside thehorn rather than in the' waveguide assembly is understood to be that the design tolerances within the radar plumbing itself arethereby rendered less critical; and that the whole arrangement can be manufactured more cheaply. Cossor were also showing a K-band demonstration model ofthe anti-rain technique. This used a simulated cloud consisting of a large number of &in ball-bearings pushed into a block ofexpanded Polystyrene. The general view was that although it is not particularly surprising that this technique should work wellagainst rain clouds, it is really extremely remarkable to demon- strate its effectiveness against a solid block of ball-bearings atsuch short range. Amongst new developments on show by Decca Radar is a 3 cmglide-path radar designed as an operational companion unit to the Company's Type 424 plan-position-indicating approach radar.The new glide-path radar has a display adjacent to the Type 424 azimuth but is otherwise quite an independent equipment andcan, therefore, be added to existing 424 radars whilst retaining freedom to be placed on the operationally most desirable site.It is understood that the Mk 1 version of the 424 radar is in use at over 60 airfields, and this year the Mk 2 made its appearance.The Mk 2 version incorporates "anti-rain" provisions in the form of a variable polarization control (i.e. circular, elliptical or linear)for the prevailing weather conditions and also a new antenna system to reduce permanent-echo clutter. The overall result is asubstantial improvement in operational utility, and maintenance of service, in conditions of rain or snow, not previously possible.Altogether the marriage of the improved Type 424 radar and the new glide-path radar provides a complete and flexible finalapproach and local airfield control system. A Decca exhibit of very great versatility was the applicationof their further developed "InterScan" fixed-coil P.P.I, display techniques to an M.R.75 radar. The M.R.75 is by now wellknown, but the operational value of this or other radars when applied with the "InterScan" facilities is very considerablyenhanced. Basically, the use of the fixed coil P.P.I, technique permits the addition of information to the display separatelyand independently from the basic radar returns with a universality not possible with the conventional rotating coil P.P.I, display.The "Interscans," so called because they are introduced in the dead time between sweeps of the time-base can be of any desiredgeometric shape—lines, circles, triangles, etc.—and by their use targets may be tracked, speed measured, bearing and range rela-tive to fixed points or to other targets accurately measured, and information transferred in positively identified form to associatedradar positions. Altogether a very versatile and flexible tool for which the air traffic controllers will come to develop a wide varietyof uses. An addition to the range of meteorological radars is the newDecca wind-finding radar. The prototype was on show with its balloon-borne corner reflector. This is understood to be the firstprimary radar designed from the outset for wind-measurement purposes, a topic already of great and increasing interest andimportance for jet operations. The radar is a 3 cm equipment using a large dish to give a one-degree beam, the beam itself beingaditionally spun about the axis to describe a cone of one degree angle. The display is on a 9in I-scope on which the signalappears as a segment of a circle, the radius of which gives range and the length of which is governed by the aiming error, so thatwhen the radar is on target the circle is complete. A valuable feature of the design is the provision made for
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