| 摘要 |
1,075,400. Selective signalling. TELEFUNKEN PATENT - VERWERTUNGS G.m.b.H. Dec. 4, 1964 [Dec. 6, 1963], No. 49404/64. Heading G4H. In a selective calling system a call signal consists of three groups of pulses of a first frequency # 1 each group being separated from its neighbour by a pulse of a second frequency # 2 . At a receiver designed to respond to a particular call signal the pulses of the first frequency # 1 are filtered and counted in a single counter and three gates are so arranged that, providing the particular call signal is received, at the end of each group one gate is opened by the counter whereby each separating pulse of frequency # 2 can pass to a further device which responds if it receives all three separating pulses within a certain period to activate a call device (e.g. a buzzer). |
