| 摘要 |
1518473 Selective signalling TELEFONAKTIEBOLAGET L M ERICSSON 1 Feb 1977 [9 Feb 1976] 04112/77 Heading G4H [Also in Division H3] A reference generator (Fig. 2) for a multifrequency receiver discriminates against interference frequency bursts by their duration. The receiver has, for each possible frequency, in parallel, a band-pass filter feeding a rectifier feeding a comparator, the comparators also receiving the reference Uref from the reference generator (Fig. 2) which is fed with the receiver input I. In Fig. 2, RL is a full-wave rectifier, G1 and G2 are gates each of which passes the larger of its two inputs, CF1 and CF2 are comparators, DF1 and DF2 are attenuators, RC is an RC circuit, and Ut1 and Ut2 are reference levels. Initially, the RC input to CF2 is less than Ut2 so CF2 provides the larger of its two possible outputs which will be the larger of the two inputs to G2 so Uref will equal it and there will be no output from the receiver. However if a signal is received at I, its peaks will exceed the lower input to CF1 thus producing pulses to charge up RC. When the charge level exceeds Ut2, CF2 provides the lower of its two possible outputs so Uref will become equal to the left input to G2 so there can be outputs from the receiver. |
