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The March of Radio
275
Guiding Our Mail Planes
E SCARCELY realize the extent to which aviation is gradually working itself into the transportation scheme of our country. Trips of the air route-mail carriers are now expected as regularly as those of the mail cars. It is evident that fog and snow present very great danger to the air mail carrier, and that anything which will increase his safety must be developed and utilized as soon as possible. The General Electric Company has undertaken the development of transmitting and receiving sets which are suitable for airplane installation, and tests recently carried out indicate that two-way communication from plane to ground may be reasonably expected with these sets, up to a distance of about one hundred miles, under average conditions.
One contribution to the safety of the airmen, which has had no wide application up to the present, is the "radio beacon"; this is a transmitting station, located at a landing field, which sends out signals in such a manner that when an aviator picks up the signal he knows at once his bearing from the field. In its present form, the radio beacon consists of a transmitter which sends out directional signals, the direction of transmission being adjustable. A characteristic signal, say two dots, is sent due north for a second or two and then the station is silent; five seconds later the two dots are again sent out, but the maximum signal is now a certain number of degrees from north, say thirty degrees west of north. This process is repeated until the signal has been sent all the way around the compass and then after a longer silent period another cycle of signals is sent out. As soon as an aviator comes within the range of such a radio beacon he can at once tell his bearing from the landing field. These beacons will probably be installed at the air mail fields as soon as funds are available .
WGY and KDKA Recommended as Wavelength Standards
A
A result of the supervision the Bureau of Standards has been exercising over some of our broadcasting stations, they have found that two of the better known stations have maintained their frequency sufficiently constant to enable them to be recommended as secondary wavelength standards. For those who are within range of the Bureau of Standards, of course, observations of the
A RADIO COMPASS RECEIVING STATION
At Sandy Hook, N.J. The operator is shown turning the wheel which adjusts the position of the big loop aerial. This station is connected by land wire to the control
station shown on page 274
standard frequencies periodically transmitted from WWV give the best method of calibrating a receiving set, but WGY and KDKA have kept their assigned frequencies so closely that for ordinary purposes, their daily transmission may be used. WGY sends on 790 kilocycles, has a maximum observed deviation from this frequency of 0.5 per cent, and an average deviation of only 0.2 per cent. This means that the carrier wave of this station is, on the average, within one meter of 379 meters. KDKA transmits officially on 326 meters and her carrier wave is generally within one meter of this specified wavelength.
These two stations then may be used as frequency standards for any but the most