A rotating-vane electric field mill was used to measure the electric field at the base of a series of vehicles as they passed through the ionosphere and reentered the atmosphere. Anticipated rapid and large variations in measured electric fields required a time response of a few milliseconds and a dynamic range from 40 to 50 000 V/m. These conflicting goals were met by using a bipolar logarithmic amplifier with limited memory. Presented here is a mathematical model of the electronics, which was used to unfold the electric field values from the telemetered outputs. The instruments also met other design constraints and functioned correctly on all flights.