Modulation in Radio Telephony

After considering the general characteristics of a voice-modulated radio frequency current, there is given a systematic classification of the various methods of producing such modulation in transmitters using three-electrode vacuum tubes. The output, efficiency, stability, completeness of modulation, quality, and other characteristics of each method of modulation are studied. The apparatus and circuits used in the long distance radiophone tests at Arlington, Virginia, in 1915, are described.