HF Transformer with Triaxial Cable Shielding Against Capacitive Current

The ratio of primary inductance LM to stray inductance LS determines the relative bandwidth Br and the pulse response of the transformer. In order to reduce LS, a miniature coaxial cable, whose outside shield serves, e.g., as the primary winding and whose inside conductor serves as the secondary winding, can be used. The relative bandwidth Br of such a transformer is then limited mainly by the mutual capacitance between both windings. When a triaxial (shielded coaxial) cable is used instead of a coaxial cable and when the internal braid is used as a shield and connected so that it has the same instantaneous HF potential with respect to ground as the internal conductor, then the mutual capacitance is practically zero and a shielded HF transformer with a relative bandwidth well over 10⁴can be constructed. This construction, which was developed for precise and fast pulse circuits, can be used whenever a floating pulse or wide-band HF signal source is needed.