| 摘要 |
To improve reliability of recognition of an announcement recognition (AR) signal radiated by a transmitter upon broadcasting an announcement (e.g. traffic information, news, etc.) in the form of AM modulation of a 57 kHz auxiliary subcarrier, in which the subcarrier is essentially continuously modulated by region or radio-station recognition signals, the level of which changes when the announcement recognition signal is radiated, the subcarrier is filtered in the receiver, demodulated, and the degree of modulation by the frequency characteristics of the region or radio-station recognition frequency (RR) is sensed. If the modulation of the subcarrier at this frequency or frequency band (RR) drops from, for example, 60% modulation to 30% modulation, or less-a 50% level change-a switch (4) is activated which inhibits transmission of audio programs from an external source, such as a tape recorder (5), a tuner tuned to another station, or the like, and reproduces the program or announcement being broadcast by the station to which a region or radio-station recognition frequency is assigned. Termination of the AR signal (FIG. 3: t2), forming the AR modulation on the 57 kHz subcarrier, causes the switch (4) to revert for reproduction of previously controlled audio information upon increase in the level of the RR modulation on the subcarrier, which is sensed in a modulation sensing circuit or network (FIG. 2: 34-37).
|
