| 摘要 |
957,019. Phase modulation; single sideband systems; frequency changer systems. L. R. KAHN. May 13, 1960 [May 15, 1959], No. 17058/60. Drawings to Specification. Headings H3F, H3R and H4L. In a phase modulated carrier, e.g. S.S.B. system in which the carrier is transmitted after frequency multiplying by one (say N) of several preselected factors the phase modulating signal frequencies are kept constant by frequency dividing, by a fixed large factor D, the initial modulated carrier and then multiplying by an D D integer - where - is switchably selectable in N N accordance with the final frequency multiplying factor N of the transmitter. Thus, if N D equals 1, 2, 4 or 8, D may be 8 and - then N equals 8, 4, 2 or 1. Frequency changing may be operated selectively with the first frequency multiplying stage so that the transposed frequency lies within the pass band of subsequent amplifiers, each frequency changing oscillation being derived by selectable frequency multiplying stages from a crystal oscillator. Frequency changing may also be provided to progressively change the carrier frequency in the pass-band before final frequency multiplication. A single sideband (with its full carrier) limited to constant amplitude may be used and the multiplied transmitted frequency amplitude modulated by the modulation envelope of the initial single side-band plus carrier derived from a diode detector; or amplitude modulated by only the fundamental frequency of the envelope of the sideband plus carrier, obtained by beating the latter with the carrier frequency in a product demodulator; the latter system being compatible with reception either in a single or a double sideband receiver. |
