Jostling for radiofrequency space

By Mark Frary

This article was originally published in the March 2006 issue of IEC E-Tech Focus, and is re-published with permission.

Ever since the first experiments with electricity and magnetism took place in the 1800s, the environment around us has become an increasingly noisy place. The advent of radio and television broadcasts in the 1900s has only added to the sea of electromagnetic waves that surround us.

Although a mobile phone interfering with a loudspeaker is annoying, there are other examples that are somewhat more serious. Research at the Center for Devices and Radiological Health at the US Food and Drug Administration found that personal digital assistants (PDAs) with wireless capabilities could affect active medical devices when in close proximity. It is research like this that underlies the ban on mobile phones in hospitals and the similar ban on using them on board aircraft.

Controlled free-for-all
Although it may seem like something of a free-for-all, the electromagnetic environment is very well controlled. If it were not, many of today’s technological advances – such as wireless internet and mobile phones – would not be possible. The key to all this is electromagnetic compatibility (EMC). This is the concept of ensuring that equipment does not cause or suffer excessive interference to or from other equipment in the vicinity.

EMC considerations cut across many of the activities of the various technical committees of the IEC but there are two committees which focus on it exclusively.

TC77 works on the general applications of EMC, including immunity over the whole range of frequencies and both low and high-frequency emissions.

CISPR is a special committee on radio interference comprising all national members of the IEC as well as the international organizations CIGRE, EBU, IARU, UIC, UIE, UITP and EURELECTRIC. The committee devises standards on equipment and methodology for measuring interference and promotes international efforts to protect radio reception from such interference.

Proliferation and RFID
EMC is becoming a more important issue all the time. This is in part due to the proliferation of electronic devices. For example, the number of mobile phones in use worldwide has now reached two billion. Also the drive towards miniaturization has seen more and more devices having radio transmitters fitted – active radio frequency identification tags are becoming big business.

It is not just the proliferation of devices that increases the workload of TC77 and CISPR.

Martin Wright is chairman of CISPR’s Subcommittee I, which covers electromagnetic compatibility of information technology equipment, multimedia equipment, and receivers.

"The basic components in devices are running at faster clock speeds and producing more radiation from an EMC perspective," says Wright. "At the same time, there is also a drive to reduce power dissipation in chips. While this is a good thing from an emissions point of view it is not so good from an immunity point of view. What you would like is the biggest signal possible so if there is interference, you can safely ignore it."

New technologies bring their own challenges. Consider Bluetooth and 802.11b Wi-Fi. Both operate in the 2.4 GHz frequency band but with different protocols. An 802.11b enabled device can be in the middle of transmitting a packet of data when a nearby Bluetooth-enabled device starts to transmit its own data. Bluetooth uses frequency hopping to try to avoid a clash but sometimes these occur, causing the Wi-Fi data packet transmission to fail. This is without taking into account the effects of microwave ovens and cordless phones, which can also transmit radiation in the same frequency band.

Power line communications
One of the big working areas for Wright at CISPR is in the provision of broadband over power lines (BPL). The concept is already popular in the US through the HomePlug alliance but is increasingly being looked at around the globe.

The basic idea is that data can be transmitted over power lines by using different frequencies from that used by the alternating current. There are considerable technical challenges to making this operate but as far as the EMC experts who work with IEC are concerned, the big challenge is to ensure that these systems do not create large amounts of interference.

Users of high-frequency radio communications, such as amateur radio enthusiasts, are particularly concerned that BPL could render their expensive radio sets into rather costly paperweights. "There is an awful lot of work going on to make sure that BPL works," says Wright.

Intense competition
The cost of EMC testing is becoming an increasingly significant issue for the manufacturers of electronic devices. Competition among manufacturers of personal electronic devices is intense. You only have to look at the huge number of new mobile phones and PDAs launched at the recent 3GSM Congress in Barcelona to realize just how much so.

With so much pressure on manufacturers to launch new products, there is a desire to drive the costs of complying with EMC requirements down. “There is a significant cost in testing these devices against any standard, not just EMC, but TC77 and CISPR Subcommittee A are working on technologies that will allow manufacturers to do much more efficient measurements in reverberation chambers,” says Wright. Rather than testing devices at individual frequencies, these will potentially allow a whole spectrum of frequencies to be tested in one go.

However, there are underlying standards that devices will meet that makes testing easier. “The first step in protection is to make sure they use the frequency band they are supposed to use and meet the underlying standard of, say, GSM or Bluetooth. Our job is to protect the environment so that no GSM device and no Bluetooth device is interfered with.”

Those early electrical engineers were lucky in the respect that they did not need to take much account of what others were doing. These days, co-operation on EMC is imperative otherwise the future is going to be a very noisy place.

Source: International Electrotechnical Commission (IEC).