A negative impedance repeater, particularly suited for use with non-loaded metallic transmission facilities, including a bridgedT series-shunt negative impedance gain unit, and an active impedance correcting unit for matching the impedance of the facility to the fixed image impedance of the gain unit. The impedance corrector, which may be modeled as a variable resistor (positive or negative) in series with a variable negative capacitor, is adapted to decrease the impedance of the facility below a predetermined crossover frequency, and increase its impedance above that frequency. The gain unit is arranged to provide a gain vs. frequency characteristic which is sloped to complement the attenuation vs. frequency slope of corrected transmission facilities.