RADIO BEACONS.

Star (Christchurch), Volume LXVI, Issue 20485, 11 December 1934, Page 5

RADIO BEACONS.

100 Miles is Maximum Range. ULM’S DIFFICULTY. Although practically no information regarding the radio beacon equipment available to Ulm and his companions in Hawaii is available, it seems probable that the aeroplane Star of Australia failed to benefit by the signals sent out, either because of the limited range of the beacon or because the machine was too far off its course to come within the arc of the beam. The beacon station mentioned—NßUl—is part of the equipment of the revenue cutter Itasca, and is listed as a mobile direction station. Radio beacons for the guidance of aircraft first came into use about 1926, said Mr. W. M. Dawson, of Philips Lamps (N.Z.), Ltd., in an interview with the “Evening Post.” There were several types of beacons in use, but the one most commonly used transmitted a signal that could be picked up by an ordinary receiving set. This type of beacon was established at an airport. It had two loop antennae placed in the form of a shallow angle, and transmitted two signals, one from each antenna. These signals were directed out from the antennae, and as the antennae were turned in towards one another the signals crossed and went out, leaving a space like a long widge in between. If an aeroplane were approaching the airport in a straight line the signals were of equal strength, but if it veered off its course it would pick up one signal and lose the other. The signals used were opposite in character. For instance, one signal might be dot dash and the other dash-dot. The airman would know that the one signal meant that he was to the right of his course and the other that he \sas to the left. Moreover, when the machine was directly between the two beams the two signals were superimposed. The gap 6 between tlie dot and

the dash and the clash and the dot were filled by one another and the receiving set gave out a long dash. Range Only 100 Miles. Unfortunately these signals had a comparatively short range, those generally used in America being of five miles to guide fog-bound machines into airports, or of 100 miles for work further afield. If NRUI had a range of 100 mile* the aeroplane would have to be within that distance of the islands to receive the signal, and it was quite possible that it could be much closer to the islands and still not receive the signal, because if it got far enough oIT its course it would be outside the arc of the beam. It was probable, Mr. Dawson said, that the radio equipment on the aeroplane was a Plessey set, as that was more or less standard equipment on Airspeed machines. This equipment was modern in design, and had a good range for both telegraphy and telephony. If Ulm's messages could have been picked up from two points by vessels with directional finding equipment his position would have been known. Even with one station it would be possible to get his direction, and as it was claimed he was to the north-east it appeared likely that the revenue cutter hail secured the direction, but it would not be able to tell how far away the machine was. As Used in Europe. The type of directional apparatus he had mentioned had been greatly simplified for use on established aircraft routes such as from the Continent to Croydon, Mr. Dawson said. The principle was the same, but modifications had been made to enable the pilot to pick up the beam without having to listen to Morse signals. The two signals transmitted instead of being Morse letters were simply waves of different frequency. The equipment on the aeroplane receiving the signals would be two tuned reeds behind a small window on the dashboard where the pilot could see them from his seat. One would be j tuned to vibrate when it received one of the signals and the other would vibrate 1 I When the other signal was received. Thus, | when one reed started to vibrate the i ; pilot would know that he had to swing : I to the left or right to reach the middle J of the beam, and when both were steadv he would know that he was on a straight line. On some machines a central reed

was used, being tuned to vibrate to both signals, and its vibrations marked the spot where signals of equal strength were received. Another variation of the same principle was the use of coloured lights instead of reeds. The Rotating Beam. The rotating beam used to transmit directions to 6hip6 had a rotating antenna which made contact at certain points corresponding to the points of the compass. For instance, it might transmit “N” for the north, and if a ship picked up that letter it indicated that the station was due north. If a rotating beam had been used at Hawaii it would probably have swung on to the aeroplane if Ulm had been within its Radio beam equipment would be of u*e for inland flying in New Zealand, Mr. Dawson said* but unless the range of the beam was greatly increased it would not be of much use for long sea voyages. The last two flights across the Tasman had proved that, as one of the machine* had gone to the south and the other to the north. Even if there had been a beam station at New Plymouth and the machines had been equipped to pick up the signals, they would probably have been outside the arc of the beam by the time they came within its range.