| 摘要 |
PURPOSE:To obtain automatically and correctly a transmitting characteristic in which the howling will not occur by changing a phase shifting quantity of the phase shifting circuit when howling oscillation occurs based upon a detecting circuit and a detecting output, and holding a phase change condition when the howling oscillation disappears. CONSTITUTION:A howling detecting circuit 11 is always in an action condition, and once the howling occurs, a switcher 4 is changed over, and the circuit is stable at the phase in which the howling disappears. The changeover speed of the switcher 4 can be set sufficiently fast in the scope in which the howling of several kHz can be detected by the detecting circuit 11. Thus, the time width from when the howling occurs till it is controlled can be sufficiently shortened to the extent that actually can not be heard by ears. In short, when the sensitivity of the howling detecting circuit 11 is raised and a changeover speed of the changeover of the switcher 4 is sufficiently made fast, this can be controlled so that an outrageous sound can not occur by obtaining the rise of the howling. |
