The Model FSD Frequency Shift Equipment, consisting of a Frequency Shift Keyer unit and a power supply, is designed for use with facsimile scanning apparatus and a c-w radio transmitter to provide a frequency-shifted radio frequency carrier proportional to the black and white contrast of the scanned material. In this it differs from previously evaluated frequency shift equipment used for c-w telegraphy which function primarily on two basic frequencies above and below an assigned carrier frequency on a "Mark" and "Space" principle. An investigation of basic mechanical and electrical characteristics of this equipment reveals insufficie frequency stability for satisfactory operation in Naval service, as well as deficiencies in mechanical sturdiness, accessibility, and operating convenience which should be corrected. It is recommended that further development of this equipment be undertake.
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