| 摘要 |
1,151,328. Radio receiving circuits. SIEMENS A.G. 10 April, 1968 [11 April, 1967], No. 17169/68. Heading H3Q. A radio receiver includes a frequency-selective four-terminal network in the form of an N-path filter provided with switching means for selecting any one of a plurality of bandwidth characteristics. In one embodiment the filter comprises series resistors R 1 , R 2 , Fig. 1, and shunt capacitors C 1 , C 2 , C 3 which are switched by electronic switches I, II, III, e.g. semiconductor diodes at a scanning pulse frequency from generator 4: the bandwidth is charged by shorting resistor R 2 by means of switch S. In a second embodiment three series paths are provided comprising three scanning switches 25, 26, 27 and each path comprising two alternative low-pass networks 31 and 32, 33 and 34, and 35 and 36 respectively, the network being completed by scanning switches 28, 29, 30 at the output side of the low-pass networks. The low-pass networks allow of two different bandwidths being selected by means of ganged switch S 1 . The scanning switches are driven from pulse generator 4 and during A.M. reception this is synchronized with the signal frequency by closure of switch S 2 . The arrangement may be used in the intermediate frequency circuits of the receiver. |
