Systems which re-use mains or phone wiring for communications purposes (such as xDSL, PLT or home-networking systems) are currently of interest. As well as their obvious benefits they have the potential to cause interference to radio systems, especially to receivers in the immediate vicinity.

Various limits to the emissions from these systems have already been proposed. One is already law in Germany, and covers a wide range of frequencies. Another, covering the LF/MF range, is agreed and in the process of becoming law in the UK. A CEPT Working Group, CEPT SE35, is considering the issue and is tasked with drafting an ERC Recommendation and Report - although the final decision will be made by a higher body.

This paper contains the various proposals for limits that are under discussion in CEPT SE35 at the time of writing and determines the degree of protection that they offer to reception of broadcasting services in the general vicinity of the data carrying cables. (A separate BBC R&D White Paper, no. WHP 004, considers the cumulative effects of such emissions on far-off receivers).

The conclusion is that none of the limits proposed so far offers adequate protection to broadcast reception. Unfortunately this is especially true of the limits that have already gained legal status in Germany and the UK. However, a proposal based on limiting the increase in the noise floor appears to offer promise and forms the subject of a separate paper.

It is hoped that the calculations presented here will guide regulators in setting limits to the emissions from the potentially widespread xDSL/PLT/etc. systems so that radio users may be assured adequate protection from interference.