| 摘要 |
676,276. Telephone transmission systems. STANDARD TELEPHONES & CABLES Ltd. Sept. 15, 1950 [Jan. 21, 1950], No. 22726/50. Class 40 (iv). [Also in Group XXXVI] In an arrangement for determining the amplitude of the harmonics of a variable fundamental # 0 in a complex signal, a signal representing the fundamental frequency controls a series of constant-amplitude sources of oscillations to cause them to produce frequencies F 1 +# 0 , F 2 +2# 0 , ... F n +nf n , where F 1 ... Fn are fixed frequencies. These frequencies are then mixed with the complex signal to produce frequencies F 1 ... F n having amplitudes proportional to those of the respective harmonics. The arrangement is suitable for use in a system such as that described in Specification 667,196 in which a voice signal is represented in transmission by signals representing the amplitude and frequency of the fundamental, and the amplitudes of the harmonics. As shown, Fig. 1, the fundamental frequency selector 2 feeds a circuit 3 whose output consists of a D.C. voltage proportional to the frequency of the fundamental. This voltage is fed to thermionic reactances 7, 8 ... 9 forming parts of the tuned circuits of the oscillators 11, 12 ... 13 which are thereby caused to emit constant amplitude signals of frequencies F 1 +# 0 , F 2 +2# 0 , ... F n +n# 0 . The signals are mixed with the complex wave in mixers 14, 15 ... 16, the respective harmonics beating with these frequencies to produce frequencies F 1 ... F n of amplitudes proportional to those of the harmonics. These may be converted to D.C. potentials by detectors 18, 20 ... 22 for feeding to the utilization apparatus 6 which is also fed with the fundamental frequency from the circuit 2. In a modification, Fig. 2 (not shown), the circuit 3 feeds only one thermionic reactance circuit to produce a frequency F+# 0 from which frequencies 2F+2# 0 , ... nF+n# 0 are produced by frequency multiplication for beating with the complex signal. In a further modification, Fig. 3 (not shown), even this thermionic reactance is eliminated by passing the fundamental through a limiter whose output is mixed with an oscillation F to produce the frequency F+f n . |
