Abstract: A fiber optic to electrical conversion unit includes front and rear modular design with rear card modules conditioning signals to be passed to front modules. A frame synchronization method transmits a stream of multiplexing frames and periodically inserts a synchronization word in the stream. Prediction of the next synchronizing word in the receiving unit reduces the need to search for a synchronization word in the stream. Loop current regulation in a two-wire loop between a central office and a PBX uses a transformer serially connected in the two-wire circuit with a regulation circuit which holds the current in the loop within a predetermined range to permit the transformer to be held to a relatively small size. High frequency noise bypassing is accomplished by forming capacitor loops from the power connection to the ground connection of the component near to the component.

Abstract: Front and rear modular conversion unit has a chassis including four side-walls and open and front rear ends. A motherboard printed circuit board mounted inside the chassis forms front and rear module insertion areas and has a plurality of connectors for receiving a cooperating mating connector, with the connecters mounted on both sides. Conversion card modules are mounted in the front end of the chassis and mate with the connectors to convert electrical signals to fiber optic signals. Rear card modules condition the electrical signals.

Abstract: An electrical to fiber optic conversion unit for use in a fiber optic transmission link includes a ferrous metal chassis with an open front end for receiving a plurality of conversion modules and power supply or test modules. The conversion module includes circuitry for converting electrical signals to fiber optic signals and is constructed of a multi-layer printed circuit board having top and bottom layers substantially covered with a non-current conducting chassis ground. The several internal layers of the conversion PC board include two signal layers for interconnecting components on the board, with the signal layers being separated by a power distribution layer and a interconnect layer for connecting components on opposite ends of the board. The multi-layer PC construction suppresses RF noise from the conversion module providing that the front panel of the module may be left uncovered while still achieving very low levels of RF emission.

Abstract: An electrical to fiber optic conversion unit for use in a fiber optic transmission link includes a ferrous metal chassis with an open front end for receiving a plurality of conversion modules and power supply or test modules. The conversion module includes circuitry for converting electrical signals to fiber optic signals and is constructed of a multi-layer printed circuit board having top and bottom layers substantially covered with a non-current conducting chassis ground. The several internal layers of the conversion PC board include two signal layers for interconnecting components on the board, with the signal layers being separated by a power distribution layer and an interconnect layer for connecting components on opposite ends of the board. The multi-layer PC construction suppresses RF noise from the conversion module providing that the front panel of the module may be left uncovered while still achieving very low levels of RF emission.