Today, I build a simple dufferential instrumentation amplifier consisting of TL072 and INA128. With it, I can now measure the impedance response of the OPT, choke, etc. The task is made simple by using the Syscomp CGR201’s built-in network analyzer function, which is set to sweep from 10Hz to 1MHz, and the voltages across the reference resistor (3.3k) and the primary winding the OPT are fed to Ch 1 and Ch 2 respectively. After exporting the resulting data to Excel, something like the following impedance vs. frequency plot can be plotted. From which, all the parameters of the OPT can be estimated.