An active coaxial choke for precision impedance measurements

It is well known that coaxial chokes are an essential feature of high accuracy impedance measurement systems. In the audio frequency range this is usually achieved using a few terminal pair windings wound around a high permeability toroidal core. This can increase the length of interconnecting cables substantially, increasing the cable corrections of defining leads. Tightly winding coaxial leads on a core can also change cable characteristics. In our measurement system many of these chokes will be required, and we propose an active coaxial choke that circumvents these issues.