A nonlinear amplifier is described which has been used to drive an Esterline Angus 0–1 ma. recording galvanometer as part of the automatic recording apparatus set up for taking microwave antenna patterns. The amplifier output is approximately proportional to the logarithm of the input voltage, and permits plotting a 60 db. variation in input signal. The speed of response is limited by the galvanometer movement but is adequate for obtaining a pattern through 100 degrees of azimuth in about two minutes. The plotting accuracy is better than 1 db. if care is taken to check calibration frequently.