Abstract: Coupling a plurality of transmitters operating with different carrier frequencies to a single aerial is often effected by multiplexing the output signals by means of band-pass filters in the output frequency band. The band-pass filters have one end connected to a start network and from there to the aerial via an aerial transmission line, and the other end to the transmitters via circulators. For an optimal use of the available frequency band, for making less stringent requirements on the band-pass filters and for providing a dynamic channel assignment feature, the transmitter coupler according to the invention has a first stage in the form of a digital coupler and a second stage in which multiplexing is effected, using band-pass filters. The transmitter output signals are combined in the digital coupler, in the pre-group phase, by digital signal processing, preferably using the GTFM method.

Abstract: A method and apparatus for use in a digital radio transmission system comprising stationary radio stations arranged in a cellular network and to which are assigned a plurality of mobile radio stations. Transmission of digital messages from a stationary radio station to the mobile radio stations assigned to it is effected by wide-band code division multiplex modulation, and transmission of digital messages from such mobile radio stations to the stationary radio station is effected by narrow-band frequency multiplex modulation. This reduces bandwidth requirements and improves the signal-to-noise ratio for each direction of transmission.