| 摘要 |
For digital transmission with existing AM emitters, the ITU recommends a system which functions according to a multi-carrier method (OFDM). Based on the distribution density of the amplitude values, digital multi-carrier signals have a relatively large ratio of maximum power to effective power (crest factor), in such a way that the AM emitter can only emit comparatively small digital power. Furthermore, in the event of saturation, the non-linear mode of the AM emitter causes inner band and outer band disturbances. By limiting the amplitude of the amplitude signal, the crest factor can be reduced and the inner band and outer band disturbances can be minimised. The amplitude is advantageously limited before converting the complex I/Q signal into an amplitude signal and a phase-modulated RF signal, so as not to disturb the narrow coupling between the amplitude signal and the RF signal. In this way, non-linear distortions can be minimised. By carrying out an additional filtering after limiting the amplitude, the truncated VQ signal is rounded, and especially inner band disturbances can be reduced. |
