| 摘要 |
1,230,217. Compandor system. SIEMENS A.G. 30 Sept., 1968 [28 Sept., 1967], No. 46259/68. Heading H4R. F.M. communication system with high modulation index has an instantaneous compressor before the modulator and an instantaneous expander after the discriminator. In a television system, Fig. 2, the audio signal is passed via a pre-emphasis circuit PE to a compressor Pr before a first modulation in modulator M1. The resulting signal is combined with a video signal TV in a filter network W1 before a second modulation in modulator M2 and application to an aerial via a transmitting stage S. At the receiver the received signal is demodulated in demodulator D1, the radio signal separated out in filter W2, demodulated a second time in D2, expanded in De, do-emphasized in DE to recover the original audio at NF<SP>1</SP>. The compressor may comprise, as in Fig. 3, a non-linear network VN in the collector circuit of an amplifying transistor, while the expander comprises a similar network providing negative feedback in the emitter circuit of a transistor amplifying stage, Fig. 4 (not shown). |
