| 摘要 |
983,116. Amplitude modulation systems. MARCONI CO. Ltd. Nov. 21, 1962 [April 10, 1962], No. 13780/62. Heading H3R. In a vestigial sideband modulation system, to increase the vestigial sideband, the outputs of two double sideband modulators 1, 2, DSBM are combined in carrier phase quadrature by a directional coupler UDC, and the modulators each fed by modulations in relative phase quadrature derived from a video directional coupler VDC, with modulation supplied in phase (or antiphase) to it from an input terminal IN. The input on lead 1 to VDC is fed to modulator 2DSBM with a characteristic increasing with rise in frequency, from zero to one half the input level and fed to modulator 1DSBM with a characteristic falling to one half the input as the frequency increases and the two modulation inputs to modulators 1DSBM and 2DSBM are in phase quadrature. A similar result is produced by the input 2 but with the rise and fall characteristics transposed. A double sideband results as output from UDC but if a low-pass filter LPF is inserted in one input to the coupler VDC and a compensating phase shift network PDN (without filter) in the other, a vestigial sideband output results from UDC. The couplers UDC and VDC may both be of the coupled line type. Alternatively, the carrier C1 may be applied in relative quadrature phase to the modulators and their two outputs directly combined (i.e. coupler UDC dispensed with). |
