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Household appliances and electronic equipment

Baby alarm interferes with aircraft communications

Domestic appliances interfere with amateur radio reception

Radio transmitters interfere with domestic electronic equipment

Thermostats interfering with TV and radio reception

Two FM radio stations intermodulate and interfere with garage doors

Trading standards prosecute hairdryer manufacturer

Numerous other interference problems with household equipment

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Baby alarm interferes with aircraft communications Top of page button

Description

A well-known make of wireless baby alarm is known to cause occasional interference with aircraft communication at some U.K. airports. It is not the wireless technology in the baby alarm that is the problem, it is their plug-top power supply, which uses a switch-mode converter. A faulty batch of power supplies was shipped with the baby alarms, and although they function well enough they emit powerfully on VHF radio channels used by National Air Traffic Services (NATS).

Cartoon of baby alarm and airplane

The interference is particularly difficult to detect on the ground but when NATS is informed of problems of this sort, they are able to overfly the troubled area with a specially equipped aircraft, partly funded by the Radiocommunications Agency (RA). When the aircraft has located the source of the interference, NATS will send in a specially equipped road vehicle which identifies the house concerned.

Officers from the RA then exchange the faulty plug-top power supply and send it back to the baby alarm manufacturer, who ship a (non-VHF-transmitting) replacement. It is a lot of trouble to go to for a low-cost electronic item, but flight safety requires us to do it.


Commentary

This source of interference was found to be due to a spurious oscillation that occurred when the internal cables were in a certain position. Designers should ensure that their products’ performance is not significantly affected by the minor variations that will inevitably occur during production.

Even assuming the product had been tested for radiated emissions, it is possible that the test was performed on a sample that did not exhibit the spurious oscillation, though this does not absolve the manufacturer from responsibility. It is also possible that the plug top power supply was only tested for conducted emissions up to 30MHz, in the mistaken belief that it had no mechanism to generate disturbances above this frequency.

Most plug-top power supplies these days use switch-mode power conversion technology, which involves power devices switching at between 50 and 500KHz. However, because they must switch at very high rates to maximise efficiency and minimise heat losses it is easy for them to emit significant amounts of emissions at up to 1000 times their basic switching rate. So a 100kHz switcher might give high levels of emissions at 100kHz intervals all the way from 100kHz to 100MHz.

Such plug-top power supplies must employ filters and other techniques to prevent their emissions exceeding statutory limits. Sometimes a batch is made with faulty or missing filter components, or with a design change that has not been tested for emissions. If the manufacturer is not employing QA methods that ensure that EMC compliance is maintained in volume manufacture, the ‘noisy’ power supplies can find their way onto the market.


References and links

From Tom Perry, U.K. Civil Aviation Authority, private correspondence, 2003; and information supplied by NATS and RIS.


Links to Mitigation Techniques

  Installation Design & Development Resources
Spurious suppression techniques   Click to go to Design technique Click to go to Resources technique
Filtering Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Shielding of areas and volumes Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Shielding of cables Click to go to installation technique Click to go to Design technique Click to go to Resources technique

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Domestic appliances interfere with amateur radio reception Top of page button

Description

The RSGB EMC Committee receives many enquiries from members about interference to reception of amateur radio signals.

Accordingly, the RSGB (Radio Society of Great Britain) has produced a leaflet that gives advice about identifying and locating sources of Radio Frequency Interference (RFI, also called electromagnetic interference or EMI). Issues covered include…


Commentary

Radio amateurs often receive weak signals which are only just detectable, and may therefore suffer interference from sources which would not normally affect domestic radio and TV receivers (except in areas where the broadcast signals were very weak).


References and links

“Interference to Amateur Radio Reception”, RSGB leaflet number: EMC 04, downloadable from http://www.qsl.net/rsgb_emc/emcleaflets4.html.

The above leaflet and a number of other useful information leaflets are indexed at: http://www.qsl.net/rsgb_emc/emc.html#emcaid. Even more information is available from http://www.qsl.net/rsgb_emc/ and http://www.rsgb.org.

“RFI/EMI RadioFrequency Interference/ElectroMagnetic Interference” is the title of a web page on the ARRL site that has links to a number of useful articles and other resources on preventing interference from (or to) household appliances and electrical equipment. Go to: http://www.arrl.org/tis/info/rfigen.html.


Links to Mitigation Techniques

  Installation Design & Development Resources
PCB layout to reduce emissions   Click to go to Design technique Click to go to Resources technique
Suppressing arcs and sparks Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Shielding of areas and volumes Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Shielding of cables Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Filtering Click to go to installation technique Click to go to Design technique Click to go to Resources technique

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Radio transmitters interfere with domestic electronic equipment Top of page button

Description

Radio amateurs are use radio transmitters which are quite powerful (typically between 10 and 100W RF power). Because their transmitters are usually in close proximity to their homes and those of their neighbours, they expose the electronic equipment in those houses to high levels of electromagnetic fields.

It is very common indeed for equipment in a radio amateur’s own home, and in his neighbours, to be interfered with by the amateur’s transmissions – so much so that to become a licensed radio amateur in the U.K. one has to pass an examination that includes questions on how to prevent interference with common domestic electronic equipment such as TVs and radios.


Commentary

Radio amateurs transmit in prescribed frequency bands which are not those used by radio or TV broadcasting. However, their signals are picked up by TV and radio antennas and can be strong enough to cause adjacent channel interference in radio and TV receiver circuits.

A more common cause of interference is demodulation (sometimes called audio rectification) by the audio and video circuits within the electronic equipment itself, due to the high field strengths created by the nearby radio transmitter. The transmissions are picked up by all/any cables (e.g. mains, signal, loudspeaker) acting as ‘unintentional antennas’ and injected into the circuits directly. Similar problems are sometimes observed when a cellphone is used near to an item of equipment.

Few domestic electronic products sold in Europe are shielded and filtered to achieve the same levels of immunity as, for example, a computer, because the applicable standard EN 55020 applies few if any immunity tests to many common products, such as audio amplifiers. It can be argued that complying with this standard does not ensure conformity with the Protection Requirements of the EMC Directive, so we would always advise manufacturers of such products to apply the generic immunity standard EN 61000-6-1 as well. Complying with this standard would make domestic electronic equipment much less susceptible.


References and links

“Radio Transmitters and Domestic Electronic Equipment”, a general EMC information sheet for neighbours about radio breakthrough on TV, radio, hi-fi, etc., RSGB leaflet number: EMC 01, downloadable from http://www.qsl.net/rsgb_emc/emcleaflets1.html.

“Radio Transmitters and Home Security Systems”, an information sheet for neighbours or alarm installers about the triggering of intruder alarms by radio transmitters, RSGB leaflet number: EMC 02, downloadable from: http://www.qsl.net/rsgb_emc/emcleaflets2.html.

“Dealing with alarm EMC problems - Advice to RSGB members”, advice to the user of radio transmitters about how to deal with the triggering of an intruder alarm, RSGB leaflet number: EMC 03, downloadable from: http://www.qsl.net/rsgb_emc/emcleaflets3.html.

“TV Distribution Amplifiers”, an information sheet for neighbours and TV aerial installers about solving breakthrough on home TV distribution amplifiers, RSGB leaflet number: EMC 08, downloadable from: http://www.qsl.net/rsgb_emc/emcleaflets8.html.

“Interference from amateur and other hobby radio to domestic broadcast reception: investigation procedure”, Radiocommunications Agency leaflet RA414 available from: http://www.radio.gov.uk/publication/ra_info/ra414.htm.

A number of other useful information leaflets are indexed at: http://www.qsl.net/rsgb_emc/emc.html#emcaid, and even more is available from http://www.qsl.net/rsgb_emc/ and http://www.rsgb.org.


Links to Mitigation Techniques

  Installation Design & Development Resources
Adjacent channel rejection Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Demodulation   Click to go to Design technique Click to go to Resources technique
PCB layout to improve immunity   Click to go to Design technique Click to go to Resources technique
Filtering with CM cable-mounted chokes Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Filtering Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Shielding of areas and volumes Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Shielding of cables Click to go to installation technique Click to go to Design technique Click to go to Resources technique

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Thermostats interfering with TV and radio reception Top of page button

Description

Faulty thermostats can cause annoying interference to television and radio broadcast reception – normally in short bursts, which may recur at intervals. Thermostats switching on and off in central heating systems, refrigerators or freezers can all cause interference problems but, generally, thermostats installed in central heating systems are the most common cause.

Sometimes the offending thermostat is found in the house that is receiving the interference, although there have been cases where the source of the interference has been found some distance away.

In one example, the interference signal is generated from a boiler gas control valve and its associated thermostat switching from stand-by to ON and vice versa. These systems have a typical power consumption of 3kW and can generate a low power single-phase arc when switched. This causes a short burst of radiation. When the thermostat is malfunctioning this burst of radiation can be heard as a rough rasping noise which typically lasts for a few seconds but may last for 20 seconds or more. It repeats typically every 10 minutes but in some cases, a faulty thermostat may arc several times per minute. In Figure 1, the stand-by to ON case is shown, while in Figure 2 the ON to OFF case is presented.

Figure 1Figure 1, stand-by set to on, shows burst of interference

Figure 2Figure 2, standby set to off, multiple bursts of interference

This kind of interference which is intermittent in nature is mostly noticed in relation to the reception of analogue TV signal at 500 to 850 MHz and sometimes on FM radio at 88-108 MHz. The effect of the interfering signal created by a faulty thermostat on the UHF analogue TV signal can be seen in Figure 3.

Figure 3Figure 3, two TV pictures showing clear before image and fuzzy interfered image


Commentary

The Radiocommunications Agency deals with many cases of interference caused by thermostats or the radio-suppression components fitted to them. In about 90% of these cases, the interference is attributable to thermostats in gas boilers. It seems that, as these operate in a heat-stressed environment, they are prone to more rapid deterioration than other domestic thermostats such as room thermostats, cylinder thermostats and diverter switching valves.

Thermostats and other automatic switching contacts of all sorts are a major source of noise complaints, particularly when they are faulty as in the above example. New domestic appliances are required to pass tests for “discontinuous disturbance” emissions (the current harmonised standard is EN 55014-1), but this does not guarantee that such products will remain noise-free after many years of operation. The limits for RF emissions are related in a complex way to the repetition rate and duration of the automatic switching event.

Replacing the faulty thermostat will normally resolve the problem, but a better solution is to fit suppression to all such switching contacts. This prevents the arc forming at the instant of switching and if properly designed has the side effect of lengthening the contact life, but the added cost is usually viewed unfavourably by manufacturers.


References and links

“Problems Thermostats Can Cause to Television and Radio Reception”, leaflet RA 272 from the Radiocommunications Agency, download from: http://www.radio.gov.uk/publication/ra_info/ra272.htm

Other information sheets, including RA 179 'Television and Radio Interference', are downloadable from http://www.radio.gov.uk, or from: Library and Information Service, Radiocommunications Agency, Wyndham House, 189 Marsh Wall, London, E14 9SX, U.K., Tel: 020 7211 0502/0505, Fax: 020 7211 0507, Email: library@ra.gsi.gov.uk

Example given in RA report “Design and Development of a Methodology for Efficiently Tracing the Source of Intermittent Wideband EMC Disturbances to Radio Reception”, University of Surrey, May 2000, Project no AY 3639. http://www.radio.gov.uk/topics/research/topics.htm#emc


Links to Mitigation Techniques

  Installation Design & Development Resources
Suppressing arcs and sparks Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Filtering with CM cable-mounted chokes Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Filtering Click to go to installation technique Click to go to Design technique Click to go to Resources technique

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Two FM radio stations intermodulate and interfere with garage doors Top of page button

Description

Cartoon of man trying to open his automatic garage doorsAustralia's ABC TV and Sydney's new FM radio station 'Nova 96.9' have unwittingly joined forces to meddle with remote-controlled garage doors.

VK2WI reports that hundreds of radio-controlled garage doors across Sydney have been overloaded by the ABC and Nova transmissions and some are refusing to open and close.

In several cases the doors have developed a life of their own, randomly opening and closing at all hours.


Commentary

The reason is that Nova broadcasts on 96.9MHz and the ABC TV sound signal is on 69.75MHz. When the two signals ‘mix’ in an overloaded door receiver, one of the resulting intermodulation products is a 27.15MHz signal.

Most garage door control receivers are tuned to 27.145MHz, but 27.15MHz is only 5kHz different from this and the receivers are designed for low cost and have insufficient adjacent-channel rejection to ignore this interfering frequency.

Also because of their low-cost, the garage door controls do not use sophisticated communication protocols, so can sometimes interpret the intermodulation signal as valid commands.

This causes erratic behaviour dependent upon signal content, ranging from inability to respond to the correct commands to opening and closing apparently at random.


References and links

From the ‘News’ section of the RSGB website, www.rsgb.org.uk, noticed by Graham Eckersall G4HFG / W4HFG on 6th July 01.


Links to Mitigation Techniques

  Installation Design & Development Resources
Intermodulation Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Adjacent-channel rejection Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Communication protocols to reject co-channel interference   Click to go to Design technique Click to go to Resources technique

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Trading standards prosecute hairdryer manufacturer Top of page button

Description

Hot UK of Sheffield pleaded guilty on six charges under the EMC regulations on 3 September 2002. The company fell foul of a DTI sponsored enforcement initiative, carried out by Cardiff Trading Standards officers. It follows a detailed investigation into the compliance of hairdryers, many of which still cause interference problems, despite claiming to meet the EMC Directive.

Two hairdryers failed the disturbance power test contained in domestic appliance product standard EN55014-1. They failed to meet the standard by 8dB and 4dB respectively. The second product also failed to meet the generic standard EN50081-1 by 19dB and caused visible interference with terrestrial TV reception.

Cartoon of hairdryer exhibit in court

The company was prosecuted because the products failed to meet the essential protection requirements of the EMC regulations and were incorrectly CE marked. Hot UK imports the products into the EU, and so is responsible for ensuring compliance. The company was fined £1000 for each offence, resulting in a total penalty of £6000. The maximum fine is £5000 per offence.

The prosecution is the result of a DTI sponsored project to investigate the compliance of various product types. Cardiff Trading Standards first targeted motor drives, then hairdryers, taking products from shops and putting them through a series of EMC tests. Trading Standards officers have also been investigating cordless power tools, which are also generally tested to EN55014-1. Early indications are that these products exhibit similar problems.


Commentary

Hairdryer manufacturers generally declare compliance against the EN55014-1 emissions standard, intended for domestic appliances. This standard is hardly sufficient to show that products meet the essential requirements of the EMC regulations. This is because it does not measure emissions effectively across the entire frequency range. A notable exclusion is the TV broadcast band.

(Note: EN 55014-1 is derived from CISPR14 Part 1.)

The case shows that manufacturers should be wary of simply declaring compliance to standards without assessing whether or not they will actually meet the EMC Directive’s essential protection requirements. Compliance with standards only gives a presumption of conformity with the essential requirements: if a standard is deficient, and there are still many cases where this happens, a product may cause interference even if it meets the standard’s requirements.


References and links

“EMC Prosecution by Cardiff Trading Standards”, EMC Compliance Journal, November 2002, Noticeboard: News and Information section, http://www.compliance-club.com/print.php?sid=103

“EMCTLA comments on the HOT UK prosecution”, EMC Compliance Journal, January 2003, pages 15 and 16, http://www.compliance-club.com/print.php?sid=115

“Study into how CISPR14 Part 1 (emissions form household appliances, electric tools and similar apparatus) may be improved to make it more relevant and accessible”, final report by Richard Marshall for the Radiocommunications Agency, reference AY4359, dated 13th June 2003, download via http:/www.radio.gov.uk, or directly from http://www.radio.gov.uk/topics/research/topics/emc/cispr14final.doc.


Links to Mitigation Techniques

  Installation Design & Development Resources
Filtering Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Suppressing arcs and sparks
(e.g. at motor commutators)
Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Shielding of areas and volumes Click to go to installation technique Click to go to Design technique Click to go to Resources technique
Shielding of cables Click to go to installation technique Click to go to Design technique Click to go to Resources technique

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Numerous other interference problems with household equipment Top of page button

Description

As our lives and our homes become filled with more and more technology, the likelihood of unwanted electromagnetic interference increases.

Click here to hear some interferenceEvery lamp dimmer, low-energy light bulb, hair dryer, electric drill, garage-door opener, TV, computer, microprocessor-controlled appliance, cellphone or wireless remote control contributes to the electromagnetic noise around us.

Many of these devices also accidentally ‘pick-up’ the electromagnetic noise in their environment, and may suffer reduced performance or react unpredictably to their ‘electronic neighbours’.


Commentary

Complex electronic circuitry is found in many devices used in the home. This creates a vast interference potential that didn't exist in earlier, simpler decades.

Your own consumer electronics equipment can be a source of interference, or can be susceptible to interference from a nearby source of electromagnetic noise.

Interference can also result from the operation of nearby amateur, citizens band, police, broadcast or television transmitters.


References and links

“Guidelines for Improving Television and Radio Reception” is a resource list giving advice to TV and radio dealers on dealing with interference problems. It is provided by the Radiocommunications Agency via: http://www.radio.gov.uk/publication/ra_info/ra323/ra323.htm.

“What To Do if You Have an Electronic Interference Problem”, a self-help guide for the consumer published jointly by the American Radio Relay League (ARRL), an organization representing Amateur Radio operators, and the Consumer Electronics Association (CEA), at: http://www.arrl.org/news/rfi/neighbors.html.

“Interference”, advice from the FCC’s Consumer & Governmental Affairs Bureau, is at: http://www.fcc.gov/cgb/consumerfacts/interference.html.

“Interference Handbook”, FCC Compliance & Information Bureau, covers a very wide range of interference problems and their sources, and how to track them down and stop them. Now provided by the ARRL, not the FCC, at: http://www.arrl.org/fcc/tvibook.html.

“RFI/EMI RadioFrequency Interference/ElectroMagnetic Interference” is the title of a web page on the ARRL site that has links to a number of useful articles and other resources on preventing interference from (or to) household appliances and electrical equipment. Go to: http://www.arrl.org/tis/info/rfigen.html.

“Reception Advice” is a BBC webpage with links to related pages and other information, including interference, at: http://www.bbc.co.uk/reception. Click on the ‘Factsheets’ button, or go to: http://www.bbc.co.uk/reception/factsheets/index.shtml, for a list of downloadable factsheets including some on interference.

“Planning debacle forces radio towers to seek new home”, Sydney Morning Herald, February 17 2003, Anne Davies, Urban Affairs Editor, http://www.smh.com.au/articles/2003/02/16/1045330466812.html

“Government admits radio towers, units were too close”, Sydney Morning Herald, February 18 2003, Anne Davies, Urban Affairs Editor, http://www.smh.com.au/articles/2003/02/17/1045330538774.html

“Neighbours find ABC has turned the radio up too far”, Sydney Morning Herald, February 24 2003, Anne Davies, Urban Affairs Editor.


Links to Mitigation Techniques

  Installation Design & Development Resources
Any/all EMC mitigation techniques could be relevant, depending on the application Click to go to installation technique Click to go to Design technique Click to go to Resources technique

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