| 摘要 |
PURPOSE:To surely vary the reception sensitivity with minimum number of parts by varying a current flowing to an antenna switching diode of a radio transmitter-receiver into>=3 stages and applying switching operation of>=2 current values at reception. CONSTITUTION:Terminals 51, 52 of a switch SW 5 are thrown at the transmission. In selecting resistance value R6<resistance R7, the highest current flows to an antenna switching circuit 4 and diodes D43, D44 are conductive completely. Thus, the antenna terminal 1 and the transmission section terminal 2 are connected and the terminals 1, 2 and a reception terminal 3 are opened. The terminal 51 ant the terminal 53 or 54 of the switch SW 5 are connected at the reception. In connecting the terminals 51, 53, the current made flowing to the diodes D43, D44 is smaller than the current at the transmission state and the coupling between the terminals 1, 3 approaches more than the open state at the transmission. When the terminals 51, 54 are connected, no current flows to the diodes D43, D44 to maximum the coupling quantity between the terminals 1 and 3.
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