  Generalized lock-in amplifiers use digital cavities with Q-factors as high as
5X10^8. In this letter, we show that generalized lock-in amplifiers can be used
to analyze microwave (giga-hertz) signals with a precision of few tens of
hertz. We propose that the physical changes in the medium of propagation can be
measured precisely by the ultra-high precision measurement of the signal. We
provide evidence to our proposition by verifying the Newton's law of cooling by
measuring the effect of change in temperature on the phase and amplitude of the
signals propagating through two calibrated cables. The technique could be used
to precisely measure different physical properties of the propagation medium,
for example length, resistance, etc. Real time implementation of the technique
can open up new methodologies of in-situ virtual metrology in material design.
