| 摘要 |
A multipurpose telephone has a speaker phone part(20) which is composed of a microphone(21), a speaker(24), amplifiers(22,25) and an impedance matching coil(23). The hybrid coil(12) used in the existing telephone can be used in common with the speaker phone. The unused contacts of the hook switch(15) in the existing telephone can be used to select the call mode, handset call mode or speaker call mode. The impedance matching coil(23) is connected between the output terminal of the amplifier(22) and the contact of the hook switch connected to the primary coil of the hybrid coil(12). The impedance matching resistor(26) is connected between the input terminal of the amplifier(25) and the common line of the receiver and the speaker.
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