Abstract: A method and system for transmitting and receiving a data stream using a phase or frequency modulated audio signal wherein an audio signal is modulated in at least one of phase and frequency according to the data stream and wherein the modulated audio signal is outside the range of human hearing. The modulated audio signal is combined with an audio program into a composite signal that is used to modulate a carrier. In order to receive the data easily, the audio program is filtered to accommodate the modulated audio signal. During reception, the gain of a detector is controlled by the power level of the recovered data-modulated audio signal. Recovery of the data-modulated audio stream is accomplished by first recovering the composite signal from the modulated carrier and attenuating the audio program so as to isolate the data-modulated audio signal. The isolated data-modulated audio signal is then again demodulated to recover the transmitted data.

Abstract: A method of producing light emitting diodes of high quantum efficiency in mass production by utilizing an epitaxial deposition from a small size melt such that the substrate itself serves as a saturation source. A silicon doped gallium arsenide wafer is cleaned and etched by normal means and subsequently the wafer is precoated with a properly doped gallium master melt. The coated wafers are inserted into an epitaxial furnace and the gallium master melt effects solution of a portion of the gallium arsenide monocrystal substrate and finally the entire wafer is cooled, maintaining a temperature gradient causing epitaxial growth on the substrate.