A variable gain circuit used in an in-band communication system is provided that includes a current sense pickup that is coupled to the output of a DC power source that senses current from the DC power source and provides a first output signal. A variable controlled amplifier structure, that is coupled to the DC power source, receives the first output signal and provides a specified amount of gain to the first output signal so as to produce a second output signal. A digital signal is produced using the second output having a selected frequency bandwidth.