Earthing - Grounding

Our Baluns match 75Ω coaxial networks to 120Ω twisted pair equipment. They are completely transparent to both circuits and isolate the circuits from each other. The earthing schemes we use are as follows.

TKPP32.xx Generic Balun Panels and the Front Mount Version TKPP32F.xx have the Receive and Transmit coaxial ports connected directly to frame ground, as per the ITU-U G.703 recommendations. Where the problem of different potential earths exists we can supply most of our Balun Panels with the input (Receive) ports earthed via a 0.1µF capacitor, as per NOTE 2 paragraph 9.4 of the ITU-U recommendations.

Our stand-alone Dual Path Baluns, have both Transmit and Receive ports earthed via a 0.1µF Capacitor to the shield of the RJ45 / RJ48.

Our Bespoke Balun Panels, are grounded in the manner specified by the manufacturer they were originally designed for.

Extract from the ITU-U G.703 Recommendations
9.4 Grounding of outer conductor or screen.

The outer conductor of the coaxial pair or the screen of the symmetrical pair shall be connected to the bonding network both at the input port and the output port.

NOTE 1
The cable routing is important if leaving the system block. Consult ITU-T Rec. K.27 for guidance.

NOTE 2
The direct connection of the outer conductors of coaxial cables to the bonding network at the transmit and receive interfaces may, because of differences in earth potential at each end of the cable, result in unwanted current flowing in the outer conductor, through connectors and through the receiver input circuitry. This may result in errors or even permanent damage. To prevent this problem, DC isolation may be introduced between the outer conductor and bonding network at the receive interface. The method of DC isolation must not compromise the EMC compliance of the equipment and the overall installation.

NOTE 3
The use of isolation to the bonding network is for further study.