Radio Broadcast (May-Oct 1922)

Radio Telegraphy 347 pointed out the possible utihty of such a system if appHed to lighthouses and lightships, so as to enable vessels in foggy weather to locate dangerous points around the coasts. 1 also showed results obtained by a reflected beam of waves projected across the lecture rooms, and how a receiver could be actuated and a bell rung only when the aperture of the sending reflector was directed toward the receiver. Since these tests of more than twenty years ago, practically no research work was carried out or published in regard toshort waves, so far as I can ascertain, for a very long period of years. The investigation of the subject was again taken up by me in Italy early in 1916 with the idea of utilizing very short waves combined with reflectors for certain war purposes, and at subsequent tests during that year, and afterward, I was most valuably assisted by Mr. C. S. Franklin, of the British Marconi Company. Mr. Franklin has followed up the subject with thoroughness, and the results obtained have been described by him in a paper read before the Institution of Electrical Engineers in London on the 3rd of The receiving outfit used by Marconi to demonstrate the reception of extremely short waves sent out by a directive antenna. For the demonstration, he used a loud speaker of American make so that the audience could observe the effect of his directional antenna. The signals of extremely short waves are picked up and then pass through a circuit similar to the superheterodyne and thus changed to a wavelength of six hundred meters. Although six hundred meters is the wavelength for ship use no interference is experienced from this source because only those waves which influence the detector circuit are passed on. This feature of the receiver was not pointed out by IMarconi and is therefore not generally realized April, 1922. Most of the facts and results which 1 propose to bring to your notice are taken from Mr. Franklin's paper. The waves used had a length of 2 meters and 3 meters. With these waves, disturbances caused by static can be said to be almost nonexistent, and the only interference experienced came from the ignition apparatus of automobiles and motor boats. The receiver at first used was a crystal receiver, whilst the reflectors employed were made of a number of strips of wires tuned to the wave used, arranged on a cylindrical parabolic curve with the aerial in the focal line. The tests were continued in England at Carnarvon during 1917. With an improved compressed air spark gap transmitter, a 3 meter wave, and a reflector having an aperture of 2 wavelengths and a height of 1.5 wavelength, a range of more than 20 miles was readily obtained with a receiver used without a reflector. In 1919 further experiments were commenced by Mr. Franklin at Carnarvon for which electron tubes or valves were used to generate these very short waves, the object being to evolve a directional radio telephonic system. A 1 3-meterwavewas chosen, which could quite easily be generated by the type of electron tube employed. As a result of the success of these experiments it was decided to carry out further tests over land across a distance of 97 miles between Hendon (London) and Birmingham. The power supplied to the tubes employed is usually 700 watts. The aerial is rather longer than half a wavelength and has a radiation resistance which is exceedingly high. The efficiency input to the tubes to aerial power is between 50 and 60%, and about 300 watts are actually radiated into space. With the reflectors in use at both ends, speech is usually strong enough to be just audible with a phone. J to ohm shunt across a 60-ohm tele