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Permitted Interference and EMC Limits Above 1 GHz

This study looks into Permitted Interference and EMC limits above 1 GHz in order to try to establish a “permitted noise metric” which Ofcom stakeholders might use to quantify expected interference in their licensed radio spectrum allocations, and recommend the level of this metric for various frequency bands. As demand for spectrum usage in the UK increases, this work will help Ofcom to guarantee a certain quality of the radio spectrum to the radio community in order to allow radio users to develop the maximum range of services in the limited spectrum available. In particular, Ofcom is increasingly being asked to keep the spectrum clean, define what interference can be expected in a piece of spectrum, and determine what are the causes of noise in a spectrum band.

It is not completely clear to what extent the radio spectrum is being polluted by both unintentional radiation and by spurious emissions at present. There have however, been many studies that help indicate the contribution from certain radio and non-radio equipment. ITU-R P.372 defines expected noise limits in a number of environments versus frequency. ITU-R P.372 has recently been updated to include evidence of increased Man Made Noise (MMN), e.g. from cars, factory machines, office equipment etc), which tends to suggest that the number of electronic and electrical devices has grown dramatically in the UK over the past few decades.

At higher frequencies, electronic devices may radiate from many parts of the equipment and can act like an antenna array, creating narrow beams of emissions in particular directions. Electronic equipment is continuing to operate at faster clock speeds with PCs now operating at speeds exceeding 3 GHz. It is envisaged that clock speeds may continue to increase up to the 10 to 20 GHz range. Other trends such as the usage of switched mode power supplies (SMPSs), switched electronic load controllers (SELCs) used in lighting dimmer switches, variable speed control devices used in drills for instance, and electronic lighting control devices and high frequency lighting technologies, could increase the pollution of the spectrum. Future developments such as Ultra-Wide Band (UWB) and increased use of Short Range Devices (SRDs) will also add to the need to define and control the quality of the spectrum above 1 GHz.

There is already considerable use of radio communications above 1 GHz (GSM 1800, 3G, radars, Wireless LAN, etc). There are only generalized maximum limits for spurious emissions from radio transmitters and many radio standards and ITU recommendations allow spurious and out-of-band emissions above 1 GHz at fairly high levels.

There are currently no agreed standards for unintentional electromagnetic (EM) emissions from ITE equipment above 1 GHz in Europe, although suggested limits are being put forward both within ETSI and CISPR. Preliminary measurements by Ofcom’s research laboratories have demonstrated that there is increasing EM noise produced by modern non-radio devices (PCs, pdas etc) at frequencies above 1GHz.

The final report is now available.



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