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Aviation History
1956
1956 - 1370.PDF
522 FLIGHT, 21 September 1956 LOCALIZE* APMKMCtt TRANSMITTER AND AERIAL, I.L.S. for the R.A.F. FLYING CONTMl TOWER HOUSMG DEMOTE CONTROL CONSOLE Layout of the Pye ground installation, showing the alternative positions of the localizer parabolic aerials. The monitor aerials can be seen ahead of the transmitters. MARKER BEACON AERIAl AND TRANSMITTER MARKER BEACON AERIAL AND TRANSMITTER J ABOUT »5 MILES FROM Rummy ABOUT 9500ft FROM RUNWAY Pye Ground Equipment Installed at Waddington THE first of a large number of Pye I.L.S. ground installationswas demonstrated last week at R.A.F. Waddington to Britishand foreign air force and civil representatives. The equip- ment is the result of several years' intensive research and develop-ment in co-operation with the R.A.E., Farnborough, and the A. and I.E.LL, Martlesham Heath, and though it is to become astandard R.A.F. aid it is fully proved for civilian applications and has, in fact, been installed at Geneva and at Hatfield, Herts. Beingsuitable for use with the present airborne I.L.S. receiving equip- ment, the Pye ground installation consists of three elements, thetotalizer transmitters, glide-path transmitters and marker beacon transmitters. All three units are designed to be directed by a remote-control apparatus located in the airport control tower under the supervision of the air traffic control officer. The whole installation iscontinuously monitored, and warning of any type of failure shows immediately at the remote-control panel. The localizer aerial array, which may be set up on the runwaycentre-line or up to 400ft to one side of it, has a parabolic reflector screen which produces a single-sided localizer beam pattern. Byeliminating the back-beam in this way the localizer is more stable and simpler, has less distortion and gives a better course line.Negative feed-back from a localizer course-monitor receiver cor- rects the localizer course automatically after any minor changesin the transmitters' performance. The transmitter radiates two amplitude-modulated signals of 90 c.p.s. and 150 c.p.s. in theV.H.F. navigation band of 108 to 112 Mc/s and the carrier is modulated to a depth of 20 per cent by each tone, while theindicator in the aircraft compares the two modulation levels to give the appropriate "on course," "steer left" or "steer right"signals. The accuracy of this system depends on the accuracy of the modulation depth and, in the past, inaccuracy in measuringinstruments used for calibration has caused considerable confusion. To overcome this, Pye have produced modulation depth testequipment which makes a close approximation to absolute measurement of modulation depth, with an error of less thanone per cent. Higher standards of calibration are now therefore possible. The glide-path transmitter and aerial are set up between 300ftand 500ft away from the runway and between 750ft and 1,250ft from the touch-down threshold. They operate on a principlesimilar to that of the localizer, though the aerials are arranged to give a vertical radiation pattern. The transmitter operatesin the U.H.F. band of 328.6 to 335.4 Mc/s and is amplitude- modulated by each tone to a depth of 45 per cent. In this case,too, the modulating frequencies are 90 to 150 c.p.s. Three marker beacon transmitters operate on the standardfrequency of 75 Mc/s, with aerials radiating vertically. Their distances from touch-down are 4.5 nautical miles, 3,500ft and250ft. They are tone-modulated at 400, 1,300 and 3,000 c.p.s. respectively and keyed in accordance with I.C.A.O. standards. A comprehensive system of monitoring and alarms is built intothe Pye ground installation. The monitor receivers, whose aerials are placed in line with their respective transmitter aerials, measuremodulation depth, tone frequency and distortion in the localizer, glide-path and marker beacon signals. Alarm units are designedto prevent the transmission of an incorrect beam. They also fail safe so that even if the system is working correctly, it will auto-matically switch itself off if a fault develops in the alarm system. If a transmitter fault arises in any of the units, duplicate equipmentis automatically switched on and a warning signal produced at the control panel. Alarms will also operate if there is more than tenper cent shift in the approach path, if there is a reduction of more than 50 per cent in power output, or if there is a change of morethan ten per cent in beam width. The complete installation is intended to run continuouslyunattended, except for maintenance, and the remote-control equip- ment allows the controller to start, stop and monitor all thetransmitters. A speech channel, with a telephone hand-set at transmitter and control panel, will, in accordance with I.C.A.O.requirements, provide emergency transmitting and receiving facilities on the localizer channel. In addition to five failure-warning lights, an identification light and a "system on" light at the control panel show when all transmitters are functioning andall alarm systems are clear. Comprehensive test equipment, supplied with the installation,includes a course detector for measuring the localizer course modulation pattern, absorption Wattmeters for checking poweroutput of both main and stand-by transmitters, and the new modulation-depth test set. The Waddington installation uses a laterally offset localizertransmitter whose beam intersects the runway centre line 2,000ft out from the threshold at an angle of 5 deg. It has been arrangedin this fashion purely because of space considerations. There are only two markers, the inner of which is in the usual middle-markerposition. The glide path is sloped at 3 deg, but can be set at any slope between 2 and 4 deg. Localizer range is between 30 and50 miles at 2,000ft. Waddington is, of course, the home of No. 230 O.C.U., the Vulcan conversion unit, but at the time of the I.L.S.demonstration, there were no Vulcans on the station. Other Pye equipment exhibited in a static display included thefull range of Pye radio-communications equipment. Being shown for the first time was a new 1 kW V.H.F. ground-to-air transmitterand an industrial closed-circuit television set-up with a camera on a remotely controlled pan and tilt mounting outside the hangar.With this equipment it was possible to survey activities all round the camera as they were presented on a television tube some dis-tance away inside the hangar. Focus could also be adjusted from inside the hangar. Announcements were most effectively put acrosswith the aid of a Pye Transhailer which is a transistorized, battery- operated, hand-held loud hailer with a range of 400 yd or moreand weighing only 5 1b. NEW SURVEY EQUIPMENT THREE instruments developed and built in Toronto for aerialsurvey work were recently shown in England for the first time. Products of PSC Applied Research, Ltd., they came to Londonfrom Stockholm, where they had been on exhibition at the International Congress of Photogrammetry. One is the T301Gamble stereo plotter (named after Mr. S. G. Gamble, chief topographical engineer, Department of Mines and TechnicalSurveys, Ottawa); others were the T246 Mk 3 automatic tri-film processor, and the T232 Mk 7 instrumentation camera. PSC Applied Research, Ltd., is the Hunting Group'sCanadian instrumentation and engineering company. It was formed in 1951 from the technical division of the PhotographicSurvey Corporation, which had been set up in 1946 to under- take a contract for mapping 125,000 sq miles of Ontario forests.Applied Research products therefore stem from practical experi- ence of designing and manufacturing equipment for aerial surveywork and airborne mineral prospecting. Of particular interest to the aircraft industry, apart from airsurvey work, is the Mk 7 camera, one of the uses of which is for instrument panel recording. It has been designed for automaticrecording on 35 mm film, over a wide range of exposure and interval times. The mechanism provides a basic unit withseparate electrical circuits for opening and closing the shutter and actuating the film transport; thus a variety of remote-controlapplications is possible. Quick-change film magazines, in 100ft and 400ft capacity, are available; and the shutter is of a focal-plane type, with a basic exposure speed of 1/100th sec. .
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