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A simple technique for measuring the time delay a (modulated) radio-frequency signal experiences when passing through a medium or device is described. A carrier signal at the desired frequency is (sine) wave amplitude modulated (e. g., at 2 MHz). The modulated signal is passed through the medium or device, amplitude-detected, and compared in phase with the modulating signal from which the time delay is deduced. Time delays of a fraction of a nanosecond are easily measured.