A test set has been developed which enables the degree of impedance irregularity of a high-frequency coaxial cable to be measured in terms of the return loss of echo pulses reflected from the irregularities when short pulses of carrier frequency are fed into the cable. The tester described employs pulses 0.3 microsec long, of a carrier frequency of 20 Mc/s, and can measure echo return losses of up to 90 db.