How are the phase and frequency precision characterized for Moku's phasemeter?
The frequency and phase precision of Moku's phasemeter is calculated based on the amplitude spectral density (ASD) of the measured frequency and phase time trace with a reference oscillator input at a given frequency range. For example, the frequency precision for Moku:Lab phasemeter is specified as:
This means, for an input reference signal at 5 MHz (<10 MHz), the frequency precision (ASD vertical axis) is better than f x 10 μHz/√Hz from f = 1 mHz to 1 kHz, where f is the Fourier frequency on the ASD horizontal axis. In the following figure, an ASD was acquired with a 5 MHz reference input.
From the ASD, we can see at Fourier frequency f = 1 Hz, the ASD is less than 1 x10 μHz/√Hz. It holds true for f = 10 Hz.