A phase modulator for use in a two-oscillator phase noise measurement sys is placed in the line from either the reference oscillator or the device under test. The phase modulator couples a small portion of the input signal to an amplitude modulator and phase shifter to shift the small signal by exactly...http://www.google.com.au/patents/US5101506?utm_source=gb-gplus-sharePatent US5101506 - Frequency calibration standard using a wide band phase modulator
