| 摘要 |
<p>In a wireless sound monitoring system, a sound activated switch (20) responsive to sounds over a predetermined level turns the transmitter on and generates an inaudible tone (30). A delay circuit causes the tone to be terminated before the transmitter is turned off. In the receiver a mute circuit responds to the tone to control the output of a loudspeaker, and thus the tone prevents a squelch tail from being heard. The monitoring unit includes a pulse generator to transmit the tones at regular intervals. At the receiver, if the tones are not detected in a predetermined period of time, a distinctive audio tone will be generated to alert the user.</p> |
