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De Forest Wireless Tele Graph System

audion, telephone, receiver, radio, current, telephony and united

DE FOREST WIRELESS TELE GRAPH SYSTEM, The. The inception of this system, invented by Dr. Lee De Forest, dates back to 1899. Dr. De Forest's original idea was to develop a receiver, working on an electrolytic principle, which would be entirely automatic in its actions, requiring no tapping back or decohering arrangement like the co herer, but allowing the use of a telephone re ceiver for rapid and accurate work. During the years 1901 to 1905 Dr. De Forest developed the radio telegraph system bearing his name. He was the first in this country to use alternat ing current generator and transformer at the transmitter as distinguished from the spark coil and direct current and the telephone receiver, With a "self-restoring" detector as distinguished from the filings coherer and Morse inker at the receiver station. These radical improvements put the radio art upon an •engineering basis. In 1904 all then existing records for overland wireless transmission were broken in the service 'established between the World's Fair at Saint Louis and Chicago, 300 miles. Five months later the American De Forest Wireless Tele graph Company installed five high-power 35 k.w. stations for the United States navy, op crating over distances of 1,500 miles. .The eke •trolytie receiver was in 1906 supplanted by the 'De Forest Audion or ionic current detector. The Audion and Ultraudion are more sensi live than any other types of detesters, abso lutely reliable in action and enable opera tion over distances quite impossible with other types.

In an exhausted glass bulb are a hot fila ment, a cold plate and a grid wire electrode lo cated midway between these two. In circuit between the plate and filament are connected a, "B" battery and telephone receiver. The in coming high frequency impulses to be detected are led to the grid and the filament. The nor mal negative current passing by means of ions or electrons from filament to plate is more or less interrupted by the slightest negative change impressed on the grid electrode of the Audion. 'The action is self-restoring instantly upon ces sation of the train of waves from the trans mitter. In this way an operator listening in the telephone receiver hears an exact reproduc tion of the transmitted signals. The Audion permits radio telegraphy over immense dis tances.

• In 1906 Dr. De Forest discovered that the Andion could be made to amplify weak tele phonic currents and this without any distortion of the voice. The Audion amplifier was de

veloped as a telephone repeater or relay to such a degree that in 1912 the American Telephone and Telegraph Company purchased a license under all the De Forest Audion patents for wire telephone purposes. Within a short time there after transcontinental wire telephony was an accomplished fact, an impossibility before the advent of the Audion relay. The Andion ant plifier has been pronounced by eminent tele phone engineers as the one radical innovation in the telephone art since the discovery of the microphone.

De Forest devoted most of his efforts from 1906 to 1910 to the development of radio telephony. Sixteen United States battleships were equipped with this system just prior •to their historic round-the-world cruise. From 1913 to 1916 De Forest developed the Ultrau dion receiver for undamped wave reception, and also the Oseillion, or oscillating Audion, as a source of high-frequency undamped waves, as a transmitter, especially for radio telephony. The United States navy has adopt ed the Ultraudion exclusively for all long distance reception, utilizing thousands of these bulbs each year. In 1915 there was installed at the large United States navy station at Ar lington, Va., a high power radio-telephone transmitter employing over 500 Oscillion bulbs. These high-frequency currents generated by these lamps were controlled by a small ((mas ters microphone. In receiving. stations at Mare Island, San Francisco and Honolulu, Audion amplifiers and directors were installed, and the spoken voice was heard distinctly over 6,000 miles. Thus was first demonstrated the correct ness of the prophecy made by De Forest in 1908 that transoceanic telephony would be achieved within 10 years. In 1917 attention was drawn to the discovery of De Forest that the Audion in connection with telephone re ceivers could be used as a source of musical sound. An elaborate musical instrument on this novel principle was developed. A large number of bulbs are controlled by keys cor responding to the keys of a piano. The pitch quality of the notes can be closely regulated through variable wide ranges by simple changes in the inductance and capacity connected with the various oscillating apparatus.