These are several different designs using transformers for CM Isolation and VNA Fixturing

CM-ADT is a Common mode isolation board for reducing current through KiwiSDR ground planes that can couple into differential voltage across the input and appear as unwanted ingress of signals and noise floor lift. It uses a Mini-Circuits ADT  or T1-1 Transformer.

CMHT is a Common mode isolation board for reducing current through KiwiSDR ground planes that can couple into differential voltage across the input and appear as unwanted ingress of signals and noise floor lift. It uses an inexpensive HenryTech balun. This is being tested for inter-winding capacitance against previous Mini-Circuit designs

Fixture is an SMA/coax ===> differential transformer for 50:800 ohm transformation to balanced line. This is especially for measuring the impedance of traveling wave antennas.