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We are developing a shipboard system which needs to be connected in a IT network (Unearthed neutral). In order to comply with this scheme we need to avoid negative-grounded, as all the metal enclosures and cable shielding needs to be grounded to create a protective earth and prevent electric shocks. (With the only exception of some capacitors of EMI filters). We are using isolated power supplies and differential signals for most communications, however some signals or the antenna connection are only possible using coaxial cable.

I have serious doubts about the coaxial connexions as those usually use the shield as negative/reference for the signal. How can two systems or an antenna in a ship be connected using coaxial cable and not introducing direct or indirect connections between supply lines and earth?

Connection between two racks using coaxial

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  • \$\begingroup\$ is that safety isolation (reinforced insulation) or just effective isolation? \$\endgroup\$ – Jasen Aug 12 '20 at 11:26
  • \$\begingroup\$ The isolation is required for the IT earthing. As power is isolated from chassis there is no possible connection to ground, so two faults are needed for a short circuit to occur. If we introduce one connection is like having already the first fault. As I understand the objetive is to increase the insulation as much as possible. \$\endgroup\$ – Dhargon Aug 12 '20 at 12:42
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How can two systems or an antenna in a ship be connected using coaxial cable and not introducing direct or indirect connections between supply lines and earth?

The simplest method is to use isolating signal transformers but there are isolating amplifiers as well that can be considered: -

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For antennas: if the antennas are operating at a high enough frequency then the shield on the coax can be capacitively connected to the driving circuit (or receiving circuit) without much chance of problems. Less than 100 pF is about as much as I'd dare consider without details.

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What about using BALUN and twisted pair, if it's a RF signal. Else you may have industrial isolated analog input and output. Usually you would need a barrier for communicaton to MCU (digital signal isolators - SPI/I2C/...) then a small DC/DC converter and dedicated ADC and/or DAC.

BALUN:

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Isolated SPI DAC 2Ch:

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Industrial Analog Signal Conditioners:

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