I am trying to test an input filter with the Bode 100.
Since each of the BNC’s (-) are tied together it does not seem possible to test this configuration as the (-) will short out my low side filter?
Do you know or have a configuration I can use for this test approach?
Great question. It is possible to measure this filter. You are correct that it would short through the BNC's using a traditional setup. You have a few options.
1) Use current, rather than voltage injection. For example, with a voltage source at the input and modulate current at the filter output. Measure the current at the output current divided by the input current. This will provide the transfer function. Our J2111A can create the current injection and provide a current monitor. Any current probe can measure the input current. Be sure to calibrate the measurement by placing the current probe on the J2111A lead and performing a THROUGH calibration. A Rogowski probe won't add any insertion impedance. See our PEM Rogowski probe. You could also connect the Bode 100 output to the filter output. Then use a current probe on the OUTPUT lead and a second current probe in the shorted INPUT lead.
2) Use differential probes to measure the input and output. You want low noise diff probes. We have one coming later this year. It will be our P2103A.
3) Add an isolation transformer or coaxial transformer at the filter output. The isolation impedance needs to be greater than the return side filter impedance (J2102B or J2113A might work).