| 摘要 |
PURPOSE:To decrease noise by providing a variable attenuating means in place of a main path switching circuit so as to increase the attenuation in response to noise. CONSTITUTION:When a modulating wave of a desired signal is inputted from an antenna 1, a gate potential of a field effect transistor (TR) 15 reaches a reference potential point, a reverse bias is zero and a resistance between terminals 15a and 15b is zero. Thus, the desired signal is fed to an audio circuit 7 while not being attenuated. When the level of the desired signal is decreased, a gate potential of the TR15 is a negative voltage with reverse bias, a resistance value between the terminals 15a and 15b is increased and the desired signal starts receiving attenuation. When the desired signal is weakened and noise amount is increased, the resistance value between the terminals 15a and 15b is maximized and the main path receives a large attenuator, then noise is muted.
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