| 摘要 |
PURPOSE:To prevent picture quality from deteriorating by providing the video deck of a wireless portable video device with a means of monitoring the intensity of a received signal and by generating an alarm tone when its intensity decreases below some level. CONSTITUTION:The circuit part 1 of a video deck consists of an antenna 3, a tuner 4, an intermediate frequency amplifying circuit 5, a video detecting circuit 6, a video amplifying circuit 7, an AGC circuit 8, etc.; the AGC circuit 8 applies the intermediate frequency amplifying circuit 5 with an IF.AGC voltage E1 and the tuner 4 and a monitoring circuit 2 with a front-end AGC voltage E2. The AGC voltage E2 is applied to the variable resistance 9 of the monitoring circuit 2 and its voltage variations are amplified by a DC amplifier 10 and supplied to a Schmitt trigger circuit 11. Since a driving circuit 12 drives a buzzer 13 in response to the on-off states of its output, the AGC voltage E2 drops when a video camera 14 is set away from the video deck 1 by a prescribed distance or more, thereby driving the buzzer 13. |
