Abstract: An electronic calibrator for doppler radar speed sensors and odometers comprising a variable impedance device, such as a varactor, positioned in the near-field of the radar antenna to modulate the radar probe beam, in the calibrate mode of the radar at a rate corresponding to the frequency of a doppler signal that would be sensed by the radar in its operating mode at a given speed. The impedance during the calibration mode is excited by a separate a.c. signal at a frequency corresponding to the doppler signal frequency. The output of the radar provides an indication during the calibration mode that can be adjusted to a calibrated indication corresponding to the actual speed causing a doppler signal of the same frequency as the excitation signal for the impedance.