Abstract: A test system for measuring the characteristics of an active circuit employs a pulsed bias technique for periodically biasing the input control port of the active circuit into the active region of operation. Biasing is achieved with a bias voltage that is periodically pulsed ON and OFF. An RF source is pulse modulated ON and OFF synchronously with the pulsed bias voltage and applied to the input control port of the active circuit. The pulsed RF occupies a portion of the time interval encompassed by the pulsed bias voltage. These voltages are combined and applied to the input port of the active circuit which operates only during the presence of the pulsed bias voltage and which is OFF during the absence of the pulsed bias voltage. A DC supply is utilized to bias the output port. The amplified RF power is then measured at the output port of the circuit, after the RF power has been separated from the DC bias by a non-reciprocal device.