INPUTTED LEVEL MONITORING SYSTEM OF VARIABLE ATTENUATOR

PURPOSE:To inexpensively constitute a variable attenuator, by using signals of a single frequency which is out of band of the transmitting frequency as the input of the variable attenuator. CONSTITUTION:A pilot signal and the signal of an oscillator 13, both of which have the same frequency, are inputted into a variable attenuator 1 through a hybrid circuit 8. These signals are extracted by an HPF10 and supplied to a meter 7' and a recorder 6 through an amplifier 11 and a detector 12. A controlling circuit 2 fetches the output of the variable attenuator 1, adjusts the gain of the variable attenuator 1, and maintains the output level of the variable attenuator 1 at a fixed level. Since the HPF10 can be used in this constitution, the monitoring circuit can be realized inexpensively.