Abstract: A memory unit includes a plurality of address ranges whose size and number are freely variable. For each address range, one address value is stored, as well as a start and an end address. The memory unit has an address generator which counts through the addresses from the start address to the end address. The start address and the end address are stored in an address register. By way of a code, the start and end addresses are called up in the address register and a current address value is called up in the address generator. The address generator counts through the address range until it reaches the end address.

Abstract: In optical communication systems for transmitting a plurality of broadband signals, particularly television signals, over an optical waveguide, the signals are modulated onto carriers of different frequencies, and the modulated carriers are transmitted as frequency-division-multiplex signals. The carrier frequencies lie in different frequency bands (B.sub.1, B.sub.2, B.sub.3) each of which is not more than one octave wide and which are spaced at least one octave apart. This makes it possible to adapt the system step by step to channel requirements using conventional, proven transmission equipment for the individual frequency bands.