Square‐wave phase modulation of the microwave signal which induces transitions allows one to measure velocity‐dependent frequency shifts in Ramsey resonance experiments. The output signal from the molecular beam apparatus is demodulated by a synchronous detector operating in phase with the modulation. This output is proportional to the derivative of the transition probability and provides the usual resonance signal which is used in a servo loop to keep a harmonic of a voltage tunable crystal oscillator on the central peak of the resonance. A quadrature synchronous detector operating 90° out of phase with the modulating signal provides a measure of any velocity‐dependent frequency shifts. Such shifts arise when there is a phase difference between the oscillating fields or when an electric field applied to a magnetic system produces av×&egr;shift. We have theoretically and experimentally demonstrated that this quadrature signal is proportional to the phase difference between the microwave cavities of a Ramsey apparatus with the in‐phase signal constrained at zero. We have also shown that the sensitivity of the quadrature system depends on the width of the available velocity distribution.