Title: Secret communication system employing magnetic control of signal modulation on microwave or other electromagnetic carrier wave

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Abstract: 1. A system for transmitting varying amplitude signals with a high degree of secrecy over a wave transmission medium, including a source of polarized electromagnetic waves of predetermined wavelength at the input to said medium, three transmission devices each adapted for transmitting electromagnetic waves in a given direction, and including a substance having a resonance spectrum with a strong, sharp absorption line therein including said predetermined wavelength within its frequency limits, and exhibiting strong anomalous dispersion in the immediate neighborhood of said line, a first and a second one of said devices being located at the input to said medium and the third being located at the output of said medium, means to apply an electromagnetic wave from said source to said first device in said given direction, means simultaneously to apply to said first device in the direction of wave propagation a weak magnetic field varying in accordance with the amplitude of the signals to be transmitted, in order to produce rotation effects in the applied wave proportional to the instantaneous signal amplitudes, representing signal modulation, means to apply the resulting modulated wave to the second of said devices in said given direction, means simultaneously to apply to said second device in the direction of wave propagation a strong magnetic field of such strength as effectively to cause the removal from the modulated wave in transmission through that device of the rotation effects representing signal modulation, and thus to render the signals carried by that wave secret to a high degree before the wave is transmitted over said medium, means at the output of said medium to apply the received wave to said third device in said given direction, means simultaneously to apply to said third device in the direction of wave propagation a strong magnetic field of the same strength as that applied to said second device but reversed in direction with respect thereto to reinsert effectively in the applied wave in transmission through said third device the rotation effects representing signal modulation removed by said second device, means to convert the rotation effects in the resulting wave into proportional amplitude modulation and means to detect the signals from the resulting amplitude modulated wave.


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