Midspan power delivery system for reduced emissions

A midspan power adapter is provided for use in a balanced communication system, such as an Ethernet system, where differential signals are transmitted between two devices. The adapter passes data signals through, and provides power to an end device, such as an IP phone, with significantly less contribution to the electromagnetic emissions of the system than known midspan adapters. Balance and symmetry inherent in a structured cable can be maintained by a termination network connecting center taps of a transformer and the spare pairs of both the incoming and outgoing cables to a common point. The adapter can provide power through unused wires (known as spare pair power) or by combining power with data signals (known as phantom feed). A common mode choke is included in the power feed to prevent noise currents from flowing through the power supply connections to earth ground, helping to minimize radiated noise.