| 摘要 |
1528189 Radio signalling INTERNATIONAL STANDARD ELECTRIC CORP 18 Dec 1975 [21 Dec 1974] 51874/75 Heading H4L In a radio receiver having a bi-stable 20 which if a marked message is received connects an a.f. transmission arrangement 4, 5 to the output of a demodulator 3 for a carrier wave, a signal SK occurs if a transmitter identifying signal, say 57 kHz, is received with a level exceeding a threshold switch 12, a signal DK occurs if an identifying signal say 125 Hz modulated on the transmitter identifying signal is received with a level exceeding a threshold switch 18, a delay circuit 13 delays the signal SK with respect to the signal DK and a setting circuit 19, which receives the signals SK and DK, resets the bi-stable if only signal SK occurs and sets it if signals SK and DK occur and leaves its state unchanged if no signal SK or DK occurs or if only signal DK occurs. In the car radio shown with switch 30 in position I a circuit 28 such as an electromagnetic relay or the emitter-collector path of a transistor or an arrangement controlling the gain of a.f. amplifier 4 maintains signal transmission to speaker 5. In switch position II the transmission path 28 is closed only if the radio is tuned to a transmitter marked with the transmitter identifying pilot signal 57 kHz. In switch position III the path 28 is closed only during the transmission of, e.g. traffic information marked with a message tone of 125 Hz. LED's 26 and 27 indicate that a transmitter identifying signal and a transmission marked with a message tone are received. If when bi-stable 20 has been set by outputs from SK and DK the received signal fades the bi-stable 20 maintains the condition of the switch 28 and when the received signal is again of sufficient strength as signal SK is delayed by the delay circuit 13 until after signal DK occurs that state of the bi-stable remains anchoraged. In a modification (Fig. 2, not shown) exclusive OR gate 21 and AND gate 22 of the setting circuit 19 are replaced by AND gates (35, 36) and an inverter (37) and if there is no control signal at 29 a changeover switch (33) connects the input of the a.f. amplifier 4 to the output of a cassette recorder tone source 34. |
