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220
Radio Broadcast
partment, recognized the importance of adapting printing to radio and made available for this work the facilities of the Navy radio laboratories. Much skepticism was expressed
FIG. I
The Morkrum light-weight keyboard control, designed for transmitting from an airplane
by experts in the government service as to the feasibility of operating printers by Yadio, but this was replaced by enthusiastic praise shortly after the beginning of experiments. A complete Teletype installation was made at the U. S. Naval Radio Research Laboratory, Bureau of Standards, and another complete outfit installed at the U. S. Naval Aircraft Radio Laboratory at Anacostia, D. C.
At the Anacostia Air Station, the transmitter was arranged so that the contacts on the Teletype keyboard controlled the radiation of impulses from the antenna system in groups of five impulses for each character, the sequence of the impulses distinguishing the characters. Throughout this work the usual code was entirely abandoned and the impulse code employed.
At the Bureau of Standards Radio Laboratory the Teletype was connected to a tuning arrangement in which a receiver with a local heterodyne detector and two stages of audio-frequency amplification were used. The relay employed was that developed by Mr. F. W. Dunmore, Physicist of the Bureau of Standards. The Dunmore relay in its different forms is illustrated on page 221 and is characterized
frequencies. The selectivity is so marked that three different stations transmitting on the same wavelength, but with different tone frequencies, may be copied simultaneously. The relay is adjusted to pick out the signal desired and the other tones do not interfere. The relay at the receiver controls the circuit passing through the Teletype magnet coils. The armature of the magnets sets into operation selective mechanism resulting in the printing of the character represented by the sequence of the impulses transmitted.
When transmitting by Teletype and listening in with any ordinary type of broadcasting receiver, the signals sound like a confused jumble of noises and are absolutely unreadable. In this way, the system may be said to allow perfect secrecy. A quick change of the arrangement of the letters on the keyboard, with a corresponding chang? of the type-wheel at the receiver would make it practically impossible for an outsider to make anything out of the signals.
Having obtained the successful results described, with operation between shore stations, Commander Taylor suggested the application of the system for transmission from aircraft to ships or to shore stations. At the present time one of the big problems in the Navy is to transmit accurately directions from
by selectivity to tones of particular
FIG. 2
The Teletype equipped for both transmission and reception