| 摘要 |
PURPOSE:To simplify the constitution while eliminating a pulsating noise of an AM receiver nearly to perfection, by composing a beat signal elimination circuit of a delay circuit and phase inverter circuit. CONSTITUTION:Beat signal elimination circuit 12 composed of delay circuit 13 and phase inverter circuit 14 is interposed between detector 9 of noise detection part 2 and BPF10. Denoting frequencies of input signals of circuit 13 as f1...fn and those of their delay signals as f1'...fn' (providing that when fn=nf1 and fn'=nf1' while n=1,2..., the delay time of circuit 13 is Td=1/[2f1]), relation (a) between the input and output of circuit 13 shows that f2n=2nf1 is in phase with f2n'=2nf1' and f2n-1=(2n-1)f1 is out of phase with f2n-1'=(2n-1)f1'. For the purpose, the phase of circuit 14 is turned by 180 deg. to put signal components of f2n=2nf1 out of phase for cancellation, and frequency characteristics of circuit 12 are changed as shown by (b) eventually, thereby removing a beat signal. |
