| 摘要 |
PROBLEM TO BE SOLVED: To provide an RF level control circuit which can attain a wide band, a high S/N and a high range without increasing the number of signal lines nor increasing the circuit scale. SOLUTION: A control signal 150 containing a noise 151 is superimposed on a balanced line by an operational amplifier 140 via resistances R5 and R7 of high resistance and then transmitted. In a reception mode, the signal 150 is taken out of the balanced line via the resistances R3 and R4 of high resistance and inputted to an RF signal control circuit as a signal that controls the RF signal level after the current of the signal 150 is amplified by an amplifier 130 so as to drive the control circuit.
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