| 摘要 |
This relates to "guard" arrangements for a VF receiver, especially for handling 2 x (1 out of 4) code signals from pushbutton subscriber sets. It is shown that if signals from a high-impedance source are applied to an infinite series of resonant circuits whose resonances are in geometrical progression, a guard voltage derived from the input to the infinite series can be opposed to the signal frequencies at the output and gives adequate guard against spurious signals such as speech, without the use of input band-stop filters or of resonant circuits having a precise Q value, as used in known guard circuits. |
