Analog adaptive notch filter: carrier canceler

This research work presents a novel way of realizing an adaptive noise canceler as a notch filter completely in the analog domain. The obvious advantage of using an adaptive notch filter would be the capability of tracking the exact frequency of interference as well as the ability to control the width of the null. The device will hereafter be referred to as the carrier canceler, as it will be used to track and cancel a 54.1 MHz carrier used in the Telescope Array RAdar (TARA) project, in southern Utah, for the detection of cosmic rays. The carrier canceler operates on a dual 5V power supply. The circuit has two inputs: An input from a signal generator that feeds a clean 54.1 MHz carrier reference and the second input, which is fed from the antenna at the receiver station of the TARA project. The circuit consists of a two tap Least Mean Square adaptive circuit that tracks the carrier frequency and phase to generate a clean replica of the carrier. This replica is then subtracted from the received signal to remove the carrier from it. The circuit is first tested in controlled conditions in the laboratory and then tested in the field. The results show the circuit has a null depth of 45 dB or better and has a 3 dB bandwidth of 300 Hz. Implementation issues such as DC offset of the multiplier Integrated Circuit (IC) and phase shift of all the ICs are discussed and a solution to rectify them is proposed.