File:Radio for everybody; being a popular guide to practical radio-phone reception and transmission and to the dot-and-dash reception and transmission of the radio telegraph, for the layman who wants to (14571485067).jpg

Identifier: radioforeverybod00lesc (find matches)
Title: Radio for everybody; being a popular guide to practical radio-phone reception and transmission and to the dot-and-dash reception and transmission of the radio telegraph, for the layman who wants to apply radio for his pleasure and profit without going into the special theories and the intricacies of the art
Year: 1922 (1920s)
Authors: Lescarboura, Austin C. (Austin Celestin), 1891-
Subjects: Radio
Publisher: New York, Scientific American publishing company (etc.)
Contributing Library: Boston College Libraries
Digitizing Sponsor: Boston Library Consortium Member Libraries

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been given a thorough field trial by the engi-neering department of the Western Electric Company. The radio link is a duplex system; that is to say, onemessage may be sent in each direction simultaneously.For transmitting, a fair-sized aerial is employed, as indi-cated in birds-eye view on pages 308 and 309, while for re-ceiving a loop antenna is used at each end. These loopsare of the solenoidal type, six feet square, and consist ofonly four or five turns each. To make the duplex opera-tion a success, it goes almost without saying that excep-tional measures had to be taken, otherwise the transmitterat one end would drown out the incoming signals on theloop antenna but a short distance away. The eliminationof such interference was attained by the use of differentcarrier frequencies for transmission in the two directions.Filters, amplifiers and repeaters are employed in largenumbers, the basis of all this equipment being the im-proved vacuum tube. An interesting feature of the receiv-
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314 RADIO FOR EVERYBODY ing apparatus is the provision of relays which close abuzzer alarm circuit when the filament of any vacuumtube fails. The radio transmitter employed at either end makes useof a circuit in which the oscillations are generated directlyin the antenna circuit. The modulation of the radio car-rier frequency is accomplished by what is known as theconstant current system, in which both oscillator andmodulator tubes are of 50 watts rating. These tubes areof the coated filament type, having relatively low filamentpower consumption and very constant operating charac-teristics. The transferring of the speech current from thetelephone line to the radio link is an elaborate process.Briefly, it may be described in this manner: The speechcurrent is applied to a speech amplifier tube, through anim/put transformer. The output of this amplifier is im-pressed on the grid circuits of the two parallel modulatortubes through a transformer. The action of these modu-lator tubes is tha

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