Which is the MOST effective countermeasure to prevent electromagnetic emanations on unshielded data cable?

Moving cables away from exterior windows reduces the proximity of an outside attacker but does not eliminate the electromagnetic emanation itself, leaving signals still interceptable from interior locations or with sensitive equipment.

Metal conduit acts as a Faraday cage, absorbing and grounding electromagnetic emanations before they can radiate beyond the cable run. This is a recognized TEMPEST countermeasure that physically contains RF signals, preventing interception by adversaries using spectrum analysis or van Eck phreaking techniques. It directly addresses the source of the vulnerability rather than relying on distance or obfuscation.

Power over Ethernet increases electrical power delivered for device operation and has no relationship to reducing or shielding electromagnetic emanations from data signals on the cable.

Bundling cables together does not suppress or shield individual cable emissions; signals from multiple cables can still be captured and separated by an attacker using signal analysis, and bundling may actually increase cross-talk without reducing overall radiation.