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Potential electromagnetic interference to radio services from railways - Final Report

A report for the Radiocommunications Agency by York EMC Services Ltd, University of York

Authors: T Konefal, D A J Pearce, C A Marshman, L M McCormack

Summary

It is well known that the railway electromagnetic environment is much more severe than that found in most commercial and domestic premises. However, in many instances the railway runs very close to such premises. In fact, in the example of an inner city light rail scheme the railway effectively runs along public roads, which brings it into close proximity to non-railway premises and potential victim systems.

There are concerns about radio frequency emissions from railways and their potential to interfere with the operation of commercial radio services and other equipment, such as information technology equipment. Conversely the introduction of new technology radio systems and the potential interference effects from TETRA and 3G communication systems, for example, may impair the safety and reliability of railway equipment.

Standards are available such as the CENELEC EN 50121:2000 series, which place limits on the emissions that should be seen at the railway boundary. The basis for these limits has been the actual levels measured at a number of railway locations around Europe, plus a margin to allow for measurement uncertainty, statistical variation of sites etc. This approach does not consider the wider impact on the radio spectrum but 'benchmarks' what is currently attainable. There is concern amongst CISPR and the radio community that the emission levels and measurement techniques set out in EN 50121 do not provide adequate protection to radio services.

During this study a literature survey has been carried out, in which evidence has been sought concerning electromagnetic emissions from the railway system. Some evidence has been found showing that such emissions are capable of interfering with electrical or electronic equipment and radio services operating adjacent to the railway lines. An appraisal of Railway EMC and other common EMC standards has been given. The potential for interference to commercial radio services has been considered theoretically and issues with the current measurement techniques and limits for Railways have been identified. Possible alternative measurement strategies have been postulated. Also the EMC mitigation techniques currently employed in the railway infrastructure have been reviewed and particularly the potential EMI from traction drive systems has been considered.

The general mitigation techniques used to achieve EMC have been applied to some extent to the railway on a macro scale. The limitation on the use of these has been to control EMI within the railway and achieve an EMC level of safety within the railway. The mitigation techniques have not been applied with the intention to reduce the threat of the railway to the outside world.

The findings of this study have implications for planned or existing buildings in which IT equipment will be used, where the buildings are situated very close (i.e. less than 10m) to electrified railway lines. There is a significant probability that the passing trains will interfere with PC monitors that are only a few metres away from the lines.

It is proposed that reduction of EM emissions from the railway can only be achieved by a progressive reduction in emission limits defined by the standards; this would be expected to have an effect over a number of decades.

Subjects for further research have been identified, principally the need to investigate alternative emission measurement techniques.

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Last Updated: 2006-Feb-01

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