Abstract: A parallel data transmission system (20) comprises a cable (40) which is capable of balanced mode transmission but which is driven in an unbalanced mode. The cable includes a plurality of twisted pairs of individually insulated conductors (42--42) enclosed by a metallic shield (54). The twist lengths are relatively short to cause the pairs to be decoupled sufficiently from one another to allow substantially error-free, parallel transmission over relatively long distances. Interposed between the core and the shield is a spacing member (52) which has a relatively low dielectric constant. Receiving facilities are provided for detecting whether the level of transmitted signals is above or below predetermined threshold values and for converting the received signals into one of two or more logic levels. Advantageously, this system increases substantially the distances over which substantially error-free transmission in an unbalanced mode can be accomplished.

Abstract: In an electronic coin telephone set, a fraud prevention arrangement prevents fraudulent coin tones originating at a telephone transmitter from being provided to a central office over a coin subscriber loop. The arrangement comprises a first and second transmission channel for alternately connecting the transmitter to the central office and also a fraud filter disposed in the second transmission channel. The fraud filter attenuates a selected frequency originating at the transmitter that is indicative of coin deposits. When coin deposits are not required by the central office, the transmitter is connected to the central office through the first transmission channel. When coin deposits are required by the central office, however, the arrangement connects the transmitter to the central office through the second transmission channel thereby avoiding the fraudulent generating of coin tones through the telephone transmitter.