"The 4101 is a modulation meter from WaveTek. Modulation meters measure degrees of modulation in a modulated signal.","Additional Features:","The Wavetek 4101 has a smart design to it. The meter is the popular \"red-needle\" type that’s always easy-to-read. It displays FM deviation (25 Hz to 50 kHz) and AM depth (up to 100%) quickly, clearly, and concisely. It automatically measures to 2 GHz (3 mV to 1 V). The input impedance is 50 ½. The accuracy is as sharp as you’ll need. It’s ±2% of full scale (±2% + residual FM) while measuring FM deviation (1 kHz). The accuracy is ±2% of full scale (±2% of reading + residual AM) while measuring AM depth (1 kHz). Two BNC connectors provide convenient outputs. You have an IF output from the rear panel that’s Å420 kHz at 100 mV into 50 ½. Also, an AF output (0.5 V RMS at 1 kHz) is available on the front panel and controlled by your selection of filters."