Abstract: The apparatus is a laser transmitter and receiver unit with independent adjustment of the focus of each and preservation of precise parallel alignment between the two lines of sight. The transmitter laser and the receiver photodetector are each mounted in a precisely machined two part mounting assembly. The first part of both mounting assemblies includes an objective lens and is fitted against the same precise surface of a reference fixture. The second part of each mounting assembly, holding the laser or photodetector, is connected to the first part by means of precisely mated coaxial sliding cylinders, so that the laser or photodetector can be replaced on the fixture with high accuracy. Axial adjustment of the distance of the laser or photodetector from their respective objective lenses is furnished by spacer washers inserted between the two parts of the assemblies.

Abstract: A circuit for mixing audio, video and data signals for transmission by laser link. The data signal is first modulated by frequency shift keying and then, after passing through a bandpass filter, is mixed with the audio signal and then frequency modulated at about 12 MHz. The combined signal is then mixed with the 70 MHz frequency modulated video signal, but each signal is isolated from the mixed signal by an appropriate filter so that each signal is not fed to the other source.

Abstract: A beam failure alarm and protection circuit for a laser communications link. In order to distinguish a true beam failure from a mere absence of data to be transmitted, an alternate signal is produced in the transmitter whenever no data is available for transmission. The alternate signal is of a much higher frequency than true signals and is bandpass filtered. Its absence is used at the receiver to shut down the data output and trigger an alarm if the receiver senses no alternate signal within the maximum time that a typical burst of data would terminate.

Abstract: An adjustable positioning plate for aligning a communications laser transmitter or receiver station. The cabinet is anchored to a flat mounting plate by a three point suspension consisting of a ball fulcrum at the cabinet bottom front center and fixtures at the lower rear corners of the cabinet. Each rear fixture includes a horizontal adjustment relative to a block attached to the mounting plate and a vertical screw to furnish vertical adjustment. Four springs straddling the cabinet sides and cross rods across the top hold the cabinet tightly against the three point suspension.