Abstract: A cable television network is supplemented with optical fibers and fiber termination units to communicate additional downstream digital signals and upstream signals. A drop unit for each customer premises is provided in the drop cable. The drop unit demodulates downstream signals and selects for delivery to the customer premises only those downstream signals addressed to the customer premises, modulating the selected signals using binary phase shift keying (BPSK) which provides relative immunity to noise for forwarding the signals to the customer premises. Upstream BPSK signals from the customer premises are demodulated and remodulated in the drop unit to isolate the customer premises wiring from the rest of the network.

Abstract: A cable television distribution arrangement is supplied via optical fibers with additional digital signals which are delivered to customers via coaxial drop cables modulated at frequencies above those of the conventional analog television channels. A reduction in the required number of modulators is achieved, while delivering individually selected signals to individual customers, by supplying digital signals for a group of customers to a first modulator and a pseudo dam signal to a second modulator, and selecting between the outputs of the two modulators individually for each customer in the group. Switching between the outputs of the modulators is carried out during overhead information which is additionally supplied commonly to both modulators.

Abstract: Fault checking of slave devices. All the slave devices are polled periodically by a master control circuit and their reponse is noted. The master control circuit asserts a control signal for every other poll so as to cause the slave device to invert the bits in its response signal when the control signal is asserted. The non-inversion of the bits during the period of several polls is indicative of either a fault condition or a device not present condition.