A chopperless ambient field apparatus and method is described having top and bottom sensing plates; a transistor-based device having first, second and third terminals; a first signal line coupled to the top plate and the first terminal of the device; a second signal line coupled to the bottom plate and the second terminal of the device; at least one controllable grounding circuit coupled to at least the first and second plates and to the first terminal of the device; an electrical parameter detector coupled to the second and third terminals of the device; and a protective enclosure disposed about the top and bottom plates, the device, and the detector, wherein with control of the grounding circuit, the detector measures AC fields and quasi-static DC electric fields impinging on the plates. A calibration procedure converts the unit to a DC measuring device.