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.

A separate BBC R&D White Paper, no. WHP 012, considers 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. It concludes 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.

This paper develops an alternative proposal based on limiting the increase in the noise floor, and shows how a practicably-applicable limit can be logically developed from this very justifiable starting principle. It is shown that the proposed limit provides reasonable protection to outdoor reception for all radio services. Some compromise in performance has to be accepted by listeners using antennas indoors for reception - this applies primarily to broadcast reception.

Regulators are urged to ensure that any emissions limits they bring forward provide a level of protection to radio services which is at least equal to that offered by the proposal presented here. Anything less stringent cannot be claimed to protect radio users - even this proposal involves some compromise on the part of the listeners.