| 摘要 |
<p>Apparatus for randomly offsetting the frequencies of each transmitter (104, 106, 108) in a simulcast radio communications system. The random frequency offsetting apparatus includes a random noise source (202) for generating a noise signal which is amplified (204) and low-pass filtered (206) before application separately or in combination with an information signal to the frequency modulation input of a corresponding transmitter (208). In frequency modulated systems, the noise signal and information signal are combined and modulated in the transmitters (104, 106, 108); whereas, in envelope modulated systems, the noise signal is frequency modulated in the transmitters (104, 106, 108), and the information signal is envelope modulated in the transmitters (104, 106, 108). Since the frequency of each simulcasting transmitter (104, 106, 108) is randomly varying, deep cancellation nulls created in the overlap areas between transmitters (104, 106, 108) by multi-transmitter interference will be randomly distributed in randomly varying locations. Therefore, communications between a central station (102) and remote stations (110, 112) located in the overlap areas will not be interrupted by the nulls for long periods of time, as was possible in prior art simulcast systems.</p> |
