The reader who's not already familiar with the virtual ground node mechanism is strongly adviced to read about the virtual ground monopole HF antenna and its background, prior to proceeding with the reading of this page.

The virtual ground node generator for balanced transmission lines and balanced antenna systems (B.V.G.N.G. for short) is a radioelectric circuit based on the same principals governing the virtual ground node generator for unbalanced lines and it is built around a broadband high power flux-coupled RF transformer having a 300 Ohm center-tapped balanced primary winding and a 300 Ohm center-tapped balanced secondary winding (Bal-Bal 1:1). The two central-tappings, each of them seat of a virtual ground node, are bonded together and connected to the chassis, ensuring a complete galvanic continuity amongst all the branches of this device.

This device allows to de-coupling the half-a-wave folded dipole (300 Ohm impedance) from its balanced transmission line (300 Ohm impedance) by imposing a clear-cut electric boundary for the RF signals flowing between the transmission line and the folded dipole antenna, in order for the dipole to exhibit its true bandwidth and for the transmission line not to interfere with it.
In the absence of a clear-cut boundary between the transmission line and the radiator, infact, the transmission line acts as part of the radiating circuit, inevitably, modifying its electrical length and giving it-self origin to hertzian radiation, with unpleasant consequences such as: loss of signal, radio interferences induction on the surrounding equipment and, above all, the illusion of a phenomenon of resonance of the transmission line it-self. Balanced lines are, instead, aperiodic as demonstrated here.

A folded dipole and its transmission line, de-coupled through a BVGNG - Radioscopic detection of the RF electric field generated by the radiator and absence of radiation by the balanced transmission line.

This device can be built to suit any transformation ratio. For example: to properly feed an half a wavelength open dipole with a 300 Ohm bifilar transmission line, it is necessary a Bal-Bal having an imput impedance of 300 Ohm ed an output impedance of 70 Ohm.

Moreover, the B.V.G.N.G. can be employed to generate a virtual ground node anywhere along a balanced transmission line.