Elements of radiotelephony
The phenomenal popularity into which radiotelephonic broadcasting has sprung has been the means of interesting thousands in radio transmission.
To the non-technical reader, the transmission of speech and music with no visible means of intercommunication is somewhat of a mystery. While it is mysterious it is no more mysterious than the production and recognition of Light, for radio and Light waves are of exactly the same nature.
The relation of radio and light waves is the same as that existing between red and blue light, it is merely a matter of frequency. Of course, the "colours" of the radio spectrum are invisible as far as the human eye is concerned and the radio receiver is nothing more than an artificial eye sensitive to these extremely low-frequency" colours."
This little volume has a three-fold purpose: first, to present in simplified form a brief discussion of what happens when messages are sent and received by radio; secondly a brief, simplified description of the apparatus required to produce these effects and how it operates; and lastly, practical unbiased information for the experimenter who desires certain results but who does not know what apparatus is necessary.
The use of mathematics has been almost entirely avoided and the treatment in most cases is qualitative rather than quantitative. For those readers who are interested in the calculation of the numerical constants of the circuits shown in the book, Circular No. 74 of the Bureau of Standards entitled " Radio Instruments and Measurements " will be found to contain valuable material. This circular may be obtained from the Superintendent of Documents, Government Printing Office, Washington, D. C. The usual conventions have been used in the circuit diagrams.
For the sake of simplicity filament-regulating resistances have been omitted from all tube diagrams. The diagrams illustrating the cm-rents and voltages in detector circuits are not intended to represent oscillograph records but have been conventionally represented.
The author is indebted to his colleague B. K. Northrop for many valuable suggestions in the preparation of the manuscript and to the American Radio and Research Corporation, the General Electric Company, the Westing- house Electric and Manufacturing, and the MuUard Radio Valve Co., London, England, for photographs of radio apparatus.
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