We present a superheterodyne-scheme demodulation system which can detect the
amplitude and phaseshift of weak radio-frequency signals with extraordinarily
high stability and resolution. As a demonstration, we introduce a process to
measure the velocity of the surface acoustic wave using a delay-line device
from 30 K to room temperature, which can resolve \textless 0.1ppm velocity
shift. Furthermore, we investigate the possibility of using this surface
acoustic wave device as a calibration-free, high sensitivity and fast response
thermometer.Comment: 5 pages, 3 figure