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Banana Skins – July 2022 (#385-393)

385. Search and rescue transmitter interferes with car alarms, central locking, and garage door openers in Las Vegas

At first the motorists of Las Vegas and neighbouring Henderson suspected that machines had taken over the world: thousands of car alarms, central-locking systems and remote garage door openers simultaneously stopped working. Local car dealerships were overwhelmed by calls from angry customers. “We were getting a hundred calls a day,” said Katie Baumann, a service operator at the Ford Country dealership in Henderson, told the Las Vegas Sun. “I tried every button everywhere. I couldn’t get it to lock. I couldn’t get it to unlock,” said Bill Zawistowski, one frustrated motorist. “Nothing I could do would make it work.”

After nearly six months, the riddle of the malfunctioning alarms and central locking systems has this week been solved by two engineers from Ford. The cause turned out to be a faulty “search and rescue” radio signal repeater located 4,000ft up nearby Frenchman Mountain, accessible only by four-wheel-drive vehicle. The radio tower had accidentally started broadcasting at 315MHz, the same frequency used by most remote keyfobs. “The repeater had been stuck on transmit probably since its last use during the winter,” said Maurice Durand, of Ford. “The relatively strong nature of the signal produced interference with many remote entry keyfobs.”

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(Reported by Chris Ayres in Las Vegas, in The Times, Saturday August 24, 2004, page 19, This conclusion followed months of fevered speculation that either UFOs or top-secret military experiments at nearby Nellis Air Base – which includes the famous ‘Area 51’military research facility – were to blame, see Roger Franklin’s article “Case of the mysterious lockout” in the “Weekend World” section of the New Zealand Weekend Herald, Saturday-Sunday March 6-7 2004,

386. LED rear lamps interfere with car radio

For some time now, owners of some lightweight British sports cars with LED rear lights have been posting complaints of interference to their AM radio reception every time they apply the brakes.

While other owners posted helpful comments such as “do not apply the brakes, it slows you down”, it was clear there was an EMC issue at the source of the problem. New cars fitted with LED rear light clusters as factory original equipment usually use some form of pulse width modulation (PWM) power control to adjust the brightness of the LEDs. For instance, where the distinction is necessary between night-time rearward illumination and full brightness braking illumination. 

It seems to be this PWM control (and associated harmonics) causing the problem in the 100s of kHz region on these sportscars. Some of the manufacturers are now selling owners inductive jump connectors for the wiring loom controlling the rear lights, at £20 for a pair, to suppress this interference.

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(Sent in by Alex McKay, by email, 31st July 2006. The editor supposes it is only natural for British sports car drivers to listen to AM radio.)

387. New UK advice on mobile phones in hospitals

Britain’s Medicine and Healthcare products Regulatory Agency (MHRA) has issued a statement on the use of mobile phones in hospital settings. In a departure from long-held conventional wisdom, the Agency does not recommend a blanket ban on mobile phones in hospitals. The statement goes on to say, however, that “under certain circumstances, the electromagnetic interference from a mobile can affect the performance of some medical devices.” 

The MHRA recommends that hospitals and trusts develop local rules to minimize the risk of interference with critical care equipment, and the Agency has developed two posters that can be displayed for safe use of mobiles. The use of mobile phones is not recommended in critical care areas such as intensive therapy units and special baby care units, or where patients are attached to complex devices. 

(From Interference Technology e-news, 28th July 2006.)

388. Solar flares can interfere with GPS, with serious consequences

Solar flares can drown out GPS signals, with potentially serious consequences for airlines, emergency services, and anyone relying on satellite navigation. It turns out that these bursts of charged particles, which produce auroras and geomagnetic storms, also generate radio waves in the 1.2 and 1.6GHz bands used by GPS. 

How was such a clash missed? Because GPS receivers only became common during a period of low solar activity. By 2011 solar flares will reach the peak of their cycle and receivers will likely fail. Or so Alessandro Cerruti of Cornell University, New York, told a meeting of the Institute of Navigation in Fort Worth, Texas, last week. The only solution would be to redesign GPS receivers or satellites, which may not be practical, says Cerruti.

(From ‘Technology’, New Scientist, 7th October 2006, page 27, Cerruti’s claims were also reported in ‘News’, Electronics Weekly, 11th October 2006, page 4, The editor keeps being surprised by how many organisations are using, or planning to use GPS for safety-critical functions, despite its well-known unreliability – reported in numerous previous Banana Skins.)

389. TV blackouts aren’t Tetra’s fault

I have been following recent correspondence in E&T about the Airwave Tetra System with interest. The interference with television signals that Alan Gordon described in the September issue is not, it seems to me, related to the standard of the installation of the Airwave equipment in police vehicles, nor to its use. Rather, the problem is one of poor immunity of much domestic equipment to out-of-band radio signals. 

Lack of immunity is often most obvious where the radio transmissions have an element of amplitude modulation and so Tetra mobiles have the potential to show up this deficiency. The solution is for do domestic equipment to meet the relevant EMC standards. Currently some manufacturers simply ignore the need for proper EMC provisions. 

(From ‘Feedback’, in the IET’s Engineering and Technology magazine, October 2006, page 6, Also see Banana Skin No. 325.)

390. Microwave ovens interfere with Wi-Fi

Recently, indoor wireless communication systems in the 2.4GHz band, such as IEEE802.11b WLAN (Wireless LAN), are becoming widespread. However, this frequency band is allocated to ISM (Industrial, Scientific, and Medical) equipment. Hence, electromagnetic noises emitted from the ISM equipment may cause interference with WLAN systems. Since there are a tremendous number of microwave ovens for domestic use, oven noises often cause serious performance degradation in WLAN systems. 

(Taken from the Abstract of the paper entitled: “Reduction of Microwave Oven Interference in DS-SS WLAN Systems using Adaptive Filters”, by M. Nkatsuka et al, EMC-Europe 2004 Symposium, Eindhoven.)

391. Microwave cooker interferes with Wi-Fi

With reference to Banana Skin No.390, from my own personal experience: I have a wireless LAN at home (IEEE802.11b/g) and also a wireless video sender, to transmit composite video and audio (running in the 2.4GHz band), and also a DECT phone. All of which are happy to cohabit with no problems.

However when I use my microwave cooker, all systems are affected. The wireless LAN on my laptop loses the connection, although it continues to see the router at a good signal level, but is unable to connect. Interference on the video sender makes it completely un-watchable, and a faint crackle can be heard on the phone. This also happens around mealtimes occasionally even when the microwave is not in use, presumably due to neighbours’ microwaves? (I live in a terraced house.) My microwave carries a CE mark and is about 7 years old. The microwave is situated about 10 metres away from all the wireless systems. When I come to replace my microwave I intend to complain if the new microwave causes the same interference.

(Sent in by Stuart Nottage of Lambda UK, on Dec 5th 2006, by email)

392. FCC Part 15 unlicensed devices and interference

The Federal Communications Commission’s Part 15 rules on unlicensed RF devices and the ways in which possible interference from such wireless systems are addressed have generated an amazing amount of misinformation. Simply reading some of the comments filed by various services on how Part 15 radio devices—specifically WLANs (wireless local area networks)—interfere with their systems might seem to indicate a near-crisis situation. 

In responses and conversations, various manufacturers of licensed equipment would have us believe that such Part 15 wireless systems are as beneficent as the Black Plague. However, a thorough examination of the problem indicates that the actual issues are far less troubling—in fact, even manageable.

Yes, interference issues do exist. For example, some of the telecom companies have banned or restricted WLAN devices from their switching stations because their equipment (Part 15 unintentional radiator devices) are subject to interference from WLAN devices. The problem is not the WLAN devices themselves but the fact that the industry immunity standard used in testing these devices does not use “real world” transmitter emissions from a WLAN.

In First Report and Order 01-278, the commission required that radar detectors be certified (they were exempt as a receiver operating over 960 MHz). This action was to avoid a serious field complaint from VSAT (satellite terminal) operators whose services were being disrupted by radar detectors. Occasionally, the FCC has requested that a WISP (wireless Internet service provider) operating Part 15 WLAN equipment cease operation until a specific interference problem has been fixed.

Is the situation perfect? No, far from it, but it is not as chaotic as some people think or, at least, state in their public filings. Apparently, a bit of fear and/or melodrama is being used to advance the case for some complainants.

(Some extracts taken from “A look at Part 15 interference problems”, by David A Case, published in Interference Technology’s EMC Directory & Design Guide 2005.)

393. Interference to broadband services

Response 19.4: A telecommunications company said that Regulation 17 has the effect of meaning that a suspension notice issued under Regulation 44 can only be issued in respect of apparatus placed on the market after 20 July 2009. They are aware of numerous cases of interference to broadband services from apparatus that is faulty or from installations that are poorly maintained. They would like to see suspension 11 notices issued in all cases of interference regardless of age of equipment since there is no other legislation that protects telecommunications networks from this type of interference.

DTI Comments: Regulation 17 has been modified to follow the placing on the market and putting into service provisions of the Directive.

(Taken from: “Implementing the new Electromagnetic Compatibility (EMC) Directive in the United Kingdom”, DTI Response to the Public Consultation, December 2006, URN 06/2236.) 

The regular “Banana Skins” column was published in the EMC Journal, starting in January 1998. Alan E. Hutley, a prominent member of the electronics community, distinguished publisher of the EMC Journal, founder of the EMCIA EMC Industry Association and the EMCUK Exhibition & Conference, has graciously given his permission for In Compliance to republish this reader-favorite column. The Banana Skin columns were compiled by Keith Armstrong, of Cherry Clough Consultants Ltd, from items he found in various publications, and anecdotes and links sent in by the many fans of the column. All of the EMC Journal columns are available at:, indexed both by application and type of EM disturbance, and new ones have recently begun being added. Keith has also given his permission for these stories to be shared through In Compliance as a service to the worldwide EMC community. We are proud to carry on the tradition of sharing Banana Skins for the purpose of promoting education for EMI/EMC engineers.

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