| 摘要 |
PURPOSE:To improve the levels of transmission and reception without inviting lowering of a sidetone, and a singing margin by setting one of the two attenuators at a specified attenuation factor corresponding to the comparison- result from a signal-level comparing means and the other one at zero attenuation. CONSTITUTION:The output of a transmission codec 23 is connected to one terminal of a transformer 4 connected to the middle point of a balancing network 6 via a transmission attenuator 21 and an amplifier 22. To the other terminal of the transformer 4,a reception codec 26 is connected via a reception attenuator 24 and an amplifier 25. To a comparator 27, the output of the codec 23 and the reception-side output of the transformer 4 are inputted. In case a transmission signal is of a higher level than a reception signal, the transmission attenuator 21 is controlled to be of zero loss while the reception attenuator 24 is made at a loss of 2alpha. But if the reception signal is of higher level than the transmission signal, the opposite controlling is executed. As a result, the transmission level can be lifted without making the echo loss smaller.
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