Transmitters and receivers have 26 frequency banks with up to 16 channels each. Each of the channels in the frequency banks “1” to “20” (system banks) has been factory-preset to a fixed frequency (frequency preset). The frequency presets within one frequency bank are intermodulation-free. These frequencies cannot be changed. The frequency banks “U1”–“U6” (user banks) allow the user to store individual frequencies which are freely selectable in 25-kHz steps. It might be that these frequencies are