Self-balancing reflectometer

Abstract

A preferred embodiment of a self-balancing reflectometer is disclosed in conjunction with a system including an RF source, an RF load, and an RF transmission channel that carries RF signals transmitted by the source to the load. The self-balancing reflectometer includes a load current sampler that generates a first sample signal related to load current by a first fixed value of gain and a load voltage sampler that generates a second sample signal related to load voltage by a voltage-responsive second variable value of gain. The first sample signal is subtracted from the second sample signal and the resulting difference signal is applied to the RF port of a double balanced mixer. The RF voltage signal appearing at the load is applied to the LO port of the mixer, which generates an IF signal that varies with both rapid load impedance modulation corresponding to load data and long term basal variations in load impedance unrelated to load data. A high gain amplifier generates output data signals corresponding to the load data and an integrator generates a gain adjustment voltage which varies with the long term variations. The gain adjustment voltage is applied to the load voltage sampler to vary the second variable value of gain in a manner to drive the difference signal to zero, thus automatically balancing the reflectometer. At the balance point, the value of the gain adjustment voltage is related to the value of load impedance by a known formula. The reflectometer is selectably responsive to either the rear or imaginary component of load impedance.