| 摘要 |
Digital transmissions in the medium and short wave range show a threshold value depending on the signal-to-noise ratio above which the audio quality received is perfect and below which no audio reception is possible. In order to prevent a sudden threshold , hierarchical modulation (Graceful Degradation) is used, which is associated with disadvantages such as reduced audio signal data, reduced coverage area with high reception quality and increased price for the receiver. According to the invention, alternatives to "Graceful Degradation" are provided, whereby modulation and/or coding are influenced in the transmitter depending on the quality data of the received signal detected by a monitor station or alternative transmission frequencies are determined. Interrogation of quality data from the monitor station can be easily effected via the Internet. |
