Photographs of Old Airplane Radios

Photographs of Old Airplane Radios

From the library of Larry Brian Radka

(A Proud Possessor of an FCC First Class Radio Telephone License)

The following report on “Airplane Radio-Telephone and Telegraph Sets” was made by the Chief Signal Officer in the United States, Major-General George O. Squier, in the January 18, 1919 issue of Electrical World:

“Prior to April 1917, a few experiments had been made in which speech had been transmitted from airplane to ground by radio methods, but the apparatus involved was hopelessly crude. On may 29, 1917, the Chief Signal Officer called a conference in his office at which the project of evolving a “voice command” equipment for airplanes which should meet all the severe requirements of the military service and which should be thoroughly standardized for quantity production was definitely set in motion against time. The plan for accomplishing this was the same as in the evolution of the Liberty engine, and from the beginning, this project was regarded as one of the major creative efforts in the development of the American Air Service. The present airplane radiophone, therefore, is the result of a period of intensive development work begun shortly after we entered the war. The services of the Western Electric engineers were enlisted, and under the direction of the Signal Corps rapid development resulted in successful tests as early as August, 1917. Speech was exchanged between airplanes 25 miles (40 km.) apart in October, and sample sets were sent at once to the army in France for trial. Several thousand sets were ordered and have been completed and distributed to flying fields here and to the air service in France.

Officials making radio telephone tests from the ground to an airplane in 1917

“The satisfactory performance of this apparatus has resulted in a new type of military unit known as a voice command squadron. The commander of an air fleet directs the movements of the individual units in any manner desired. The effectiveness of the squadron as a military machine is thereby enormously increased.

“Other uses are communicating information from airplanes to ground stations and in directing one or more airplanes from a ground station. Innumerable applications will evolve as possibilities are realized.

“The essential elements of the airplane radiophone are the power equipment, the radio equipment and the antenna.

“a. The power equipment includes a double-voltage direct-current generator driven by an air fan, with a vacuum-tube voltage regulator.

“b. The radio equipment consists of the vacuum tube transmitting and receiving set and the special telephone transmitters and receivers.

“c. The antenna originally consisted of a flexible copper wire several hundred feet long, unreeled by the aviator and trailing almost horizontally behind the airplane. Modified antennas using much shorter wires fixed to the framework are now used.

A WWI type of airplane radio. Note the insulator and antenna connector

“The operation of the sets is extremely simple, all adjustments being made before leaving the ground. The only manipulation required of the aviator is that of the change-over switch to change from talking to listening.

An early aviator standing by a ground controller communicating with an airplane

“The principal use of radio communication made during the war was in sending radio-telegraph signals from observation airplanes for controlling artillery fire. The French developed a self-contained set, which has been demonstrated to be far superior to any other airplane set.

“It consists of three units—first, the 200 watt, 900 cycle alternator, driven by a regulating air fan and containing a streamline case attached to the generator and all the elements of the radio set. The radio apparatus is of the synchronous-spark type, with four spark tones and nine wavelengths. The weight of the complete unit is 23 lb. (10.4 kg.) and the size only 6 in. by 6 in. by 20 in. (15 cm. by 15 cm. by 66 cm.). The regulation air fan maintains the speed of the generator within four per cent of 4500 r.p.m. with air velocities between 60 and 200 miles an hour.

“The remaining units in the complete set are a variometer or tuning coil, with antenna ammeter attached, and the antenna system, comprising a reel, insulated bushing and trailing antennas. When it is realized that voltages of 30,000 or more are produced by this set, the difficulties of insulation in such restricted space will be appreciated. Ranges of communication of 100 miles (160 km) have been accomplished with this set.”

This was a significant distance for old airplane radios, until the age of the real high flyers.