| 摘要 |
1,189,164. Voice frequency signal receivers. INTERNATIONAL STANDARD ELECTRIC CORP. 5 May, 1967 [12 May, 1966], No. 20925/67. Heading H4R. A U.F. signal receiver includes a first limiter D1, D2 followed by a second limiter in parallel with one or more tuned circuits C4, L1 and C5, L2, the second limiter having a threshold level dependent upon the level of signals applied to it and consisting of a rectifier bridge D3 to D6 having an R.C. element across its D.C. path. For received U.F. signals above a certain level, the voltage at the R.C. element unblocks diode D7 to unblock the tuned circuit rectifying- amplifiers T3, T5 and T4, T6 which supply one input to AND-gates Af1 and Af2. The other input to the AND-gates is supplied by Schmitt trigger T7, T8 and time delay Z after the other input to either gate has existed for a certain length of time. |
