| 摘要 |
PURPOSE:To prevent occurrence of the howling through a simple circuit constitution by actuating the hook switch and thus lowering the gain of the speaker amplifier by a fixed amount in case the remote side is called out via the key telephone set for the extension loud-speaking use. CONSTITUTION:Extension loud-speaking key telephones TEL1 and TEL2 are incorporated into the handset along with transmitter T, receiver R, telephone circuit network NW and others. And hook switch HS is actuated when the handset is picked up. Then the voice supplied through microphone MIC is amplified by mike amplifier MA and then supplied to speaker amplifier SA plus channel switches SW1 and SW2 via hybrid circuit HYB. Hook switch SH is connected to amplifier SA of TEL1 and TEL2 each, and the mutual calling is given by picking up the handsets at one time. In such case, the gain of amplifier SA is lowered down to such level as to produce no howling to carry out the incoming and the voice reply. |
