A radio frequency tuner includes a first quadrature frequency changer, I and Q filters which are electronically adjustable, and a second quadrature frequency changer. During alignment of the filters, an alignment controller connects a test tone generator to the input of the frequency converter and the generator supplies a sequence of test tones of different accurately known frequencies. The amplitude of the resulting signals at the output of one of the filters is measured by a level detector. The controller compares the measured levels with a desired frequency response and adjusts the filter accordingly. The controller then causes the generator to supply a sequence of two test tones of different frequencies and a differential phase detector measures the phase difference between the output signals of the mixers of the second frequency changer. The controller adjusts the response of the other filter and the test procedure is repeated until phase imbalances between the filters are substantially reduced or eliminated.