Banana Skins – December 2019 (#230-239)

230.  GPS is so vulnerable to EMI that back-up systems are required for safety-of-life applications

The DOT/Volpe study on the vulnerability of GPS concluded that interference – either intentional or unintentional – could deny GPS access for critical infrastructure applications. It also concluded that, for safety-of-life applications, back-up systems to GPS would have to remain in place. Lacking other qualifiers in the summary text, one assumes that the back-ups are intended to remain in place indefinitely.

(From an article by Terry McGurn, former senior analyst, Central Intelligence Agency, in “Directions 2003” in GPSworld, December 2002, page 33, The “Volpe” report can be downloaded via or direct from

Vulnerability of GPS and Galileo and likelihood of jamming

The perception of the vulnerability of satellite navigation signals by both Europe and the United States seems to have changed 180 degree over the last ten years. In the 1990s, Europe was cautious about transitioning to GPS aviation landing systems, and it was Europe that pushed for the introduction of microwave landing systems (MLS) as a replacement for instrument landing systems (ILS). The key reason stated was the weakness of the signal delivered from space. The U.S. on the other hand, championed the benefits of GPS and declared that by the end of the 1990s, Wide Area Augmentation System (WAAS) and Local Area Augmentation System (LAAS) would be operational and ILS (and other navaids) a technology of the past.

Over the last year the U.S. has acknowledges that GPS is a vulnerable system, particularly to intentional and nonintentional interference, and has concluded that backup systems and techniques to find intentional interference will be required for critical infrastructure. On the other hand, Europe seems unworried by the situation and declares that Galileo (which will use the same technology as GPS) has a very good backup – called GPS.

Some also believe that the applications suggested for Galileo, such as road tolling, will promote widespread jamming by the public – with major implications for other users.

(Extracts from an article by Alan Shuster Bruce, Manager GNSS Programs, Thales Avionics UK, in GPSworld, December 2002, pages 33 and 34,

Many common sources can interfere with GPS, and jammers are easy to make

Just recently, the U.S Coast Guard and FCC confirmed that certain consumer VHF/UHF marine television antennas cause inaccurate position information or a complete loss of GPS receiver acquisition and tracking ability. On a broader scale, the FAA has acknowledged interference sources to be commercial and civilian aviation such as broadcast television, personal electronic devices, Mobile Satellite Service (MSS) communications systems, and ultra-wideband (UWB) radar and communication systems. The busier the airwaves become, the more susceptible GPS is to interference.

With electronics schematics obtained from the internet, you can go to an electronics supply store, spend about $500 and get the parts you need to build a GPS jammer that can disable the commercial use of GPS out to 100 to 125 kilometers – line of sight.

One long-term solution would be to increase satellite signal power. But those large improvements are not scheduled for another 10 years! You can now use an appliqué or antenna and electronics add-on package which removes the interference before it gets to the GPS receiver. This is what ERI provides.

(Extracts from an ‘advertorial’ by Mario M. Casabona, President and CEO of Electro-Radiation Inc. (ERI), in “Showcase” in GPSworld December 2002, page 21,

Ensembles of sources will make interference problems harder to solve 

ADSL and VDSL (broadband internet over ordinary telephone wires), low voltage lighting using ‘transformerless’ power supplies, plug-top switch-mode power supplies, variable-speed motor drives used in domestic appliances to save energy, power line telecommunications (PLT, also called PLC), ultra-wideband (UWB) radar and radiocommunications – are examples of the kinds of ‘noisy’ low-cost electronic devices and systems likely to enjoy wide adoption over the next few years.

If present trends continue (as they seem likely to) – in the not-so-distant future interference with radio communications (including safety-critical avionics systems) will no longer be identifiable or preventable as it will arise from ‘ensembles’ of many thousands of such cheap and cheerful interference sources, even if they all actually complied with the relevant emissions standards prevailing at the time they were taken into service and none are faulty (which is an unlikely situation in any case).

(From “Future Trends in EMC” presented by Keith Armstrong of Cherry Clough Consultants at the Flomerics seminar “Introduction to EMC” in Taipei, Taiwan, September 17 – 18 2002.)

The EM environment is worsening whilst vulnerability to EMI is decreasing

The environment in which we live is becoming richer with man-made electromagnetic energy and at the same time the susceptibility threshold of electronic technology is decreasing.

(From Maqsood Mohd, Chairman of the IEEE EMC Society Education and Student Activities Committee (EASC), writing in the IEEE EMC Society Newsletter, January 2003,

Military base security upgrades interfere with car immobilisers and alarms

President Bush’s son of star wars has neutralised its first targets in Yorkshire even before the British government has given the formal go-ahead for the RAF Fylingdales base on the moors to be used for the project. The upgrading of the security and surveillance systems at the base, in preparation for an onslaught of peace protesters objecting to the scheme, is knocking out the electrical systems of expensive cars.

Visitors to the beauty spot of Goathland, where the TV series Heartbeat is filmed to portray an idyllic 1960s rural life, have found themselves trapped among its charms. High power radar pulses trigger the immobilising devices of many makes of cars and motorcycles – BMW, Mercedes and Jeep among them. Many have had to be towed out of range of the base before they can be restarted.

The RAF admits it is a problem but says it is down to the car manufacturers to change their frequencies. However, Jeep claims this is not possible because of government restrictions.

Either way the locals are not amused. Frank Doyle, who owns a shop called Bazaar in Whitby, makes regular deliveries to the Goathland area in his Mercedes Vito van. He said: “I have got stuck three times in less than two weeks and have to keep calling breakdown services to get out of the place. “I am very fed up with it. It’s not just the inconvenience – it messes up the business and my social life. Now when I’m on deliveries I keep the engine running, but still can’t visit friends who live near Fylingdales.”

Goathland resident Jackie Fearnley said: “I know that car alarms do go off, but this is getting ridiculous. It is disturbing all the villagers – and I don’t think it is going to help tourism here either. Someone has got to sort this out.”

North York Moors National Park car park attendant Bill Peirson said that Jeep Cherokees, Mercedes cars and vans, and BMWs seemed to be worst affected by the radar. “As soon as the alarms go off, I go over to the owners and explain it’s probably the Fylingdales radar that’s caused it.

“Motorbikes are the worst. There was a bike alarm screaming all afternoon recently and the rider didn’t have any breakdown cover. I asked a friend in the village with a trailer to tow him away, and as soon as they were out of Fylingdales’ range, it stopped.”

Wing Commander Chris Knapman, of RAF Fylingdales, said it was not up to the base to resolve the problem. “We have had the frequencies we use for a very long time,” he said. “They are allocated to commercial, military and government users, and the allocation is very tightly controlled. As far as we are concerned, the radars are working on frequencies which are well known, and most car manufacturers take that into account.”

A spokesman for Jeep said: “The problem is that the government gives manufacturers such a narrow band to operate in – so the radio wave we use for our key fob is severely restricted.”

(From “Son of star wars leaves drivers stranded” by Paul Brown and Nigel Burnham, Wednesday December 18 2002, The Guardian Copyright, Guardian Newspapers Limited. Mike Feeney of Freeman Hospital, Newcastle on Tyne, spotted this on the Guardian Unlimited site. To see this story with its related links, go to

TV antenna boosters interfere with specialised mobile radio systems

These devices (active television antenna profiled in January 2003 GPS World article) can also interfere with specialized mobile radio (SMR) systems. We have a cell site near Mission Bay in San Diego. A few months ago we started getting interference on several of the channels in this site. The interference was centred around 815MHz and was about 2MHz wide.

Two days of sniffing it out with a spectrum analyzer was required. The boat owner was on an extended trip but allowed us to disconnect the offending antenna.

(Rich Reinhofer, Supervisor RF Operations, Nextel, San Diego, writing in GPS World, March 2003, page 8, The article he is referring to was summarised in Banana Skins No. 222.) 

TV antenna boosters interfere with cell phone systems

I’ve also been involved in hunting down interference caused by active television antennas. In my case, the interference was to a cellular telephone system and the TV antennas were mounted atop RVs (Recreational Vehicles – Editor) at mobile home parks. The unit(s) causing interference were in some cases more than two miles from the cellular phone site that was receiving interference.

If what you were tracking (see Banana Skin 222 – Editor) was the second harmonic of the signal from the oscillating amplifier, the signal only has to drift a small amount for the fundamental signal to cause interference to the base station receivers of cellular telephone, public safety, and business radio systems operating in the 806-849 MHz band.

IS-95 CDMA cellular telephone systems are extremely sensitive to this type of interference. In my company’s case, finding the offending devices and getting them turned off is worth a nearly unlimited effort.

Author’s reply: The emissions from the antenna we studied in detail had a fundamental frequency near 1575 MHz. This was not a harmonic. Its precise frequency depended upon temperature and other environmental variables. The other two antennas also had temperature-dependant frequencies near to the GPS L1 frequency, but we did not study them in a laboratory environment. We do not know that this was the fundamental frequency for the other two RFI sources, but that is likely. – Jim Clynch

(Eric Lawson, Senior Engineer, Alltel Communications, writing in GPS World, March 2003, with reply, Page 8, Note that in the USA all the personal cellphones operate around 1.9GHz, but they have a number of other specialised cell-based telecommunication networks operating in the 800-850 MHz region, including a country-wide system for use by police and other emergency services, see Banana Skin No 179.)

TV antenna boosters causing interference to GPS etc. identified by US Coast Guard

We are currently looking at numerous applications for GPS on board locomotives. I was quite interested in the recent article “The Hunt for RFI” but was quite disappointed that it did not list the model or manufacturer’s name of the offending pre-amplifiers as we may want to put out a bulletin to determine if any of these devices are installed in our railroad yards or office cars. Is this information available? (Gary G Wilson, RF Systems Engineer)

I have been involved with tracking similar problems with interference to radio systems here in Indianapolis, Indiana area. The cause of the interference has been traced to defective manufactured RV television antennas. The article did not mention the manufacturer of the antenna. Could you pass along my query about the manufacturer? (Bill Atkin)

Names of the equipment jamming GPS were not published in the January article for liability reasons. The U.S. Coast Guard now has a safety notice listing brands and model numbers of known emitters. You can reach this site via by going to GPS, Notes, and Information. The list may not be complete, however. The model traced by Bill Atkin is not on it. The FCC tracked the preamplifiers in three jamming antennas to an overseas factory owned by a subsidiary of a U.S. company. It is believed that the bad units began with a design change in late 2000. The number of units sold is not known, but they went to at least five different companies producing consumer goods.

(Two letters published in GPS World, March 2003, page 8, with a reply from that publication’s editor, See Banana Skin 222 for the article that began this correspondence. Another site for the US Coast Guard report used to be:

Complying with immunity standards might not defend against product liability lawsuits

The following jurisprudence shows how negligence can be interpreted. In the Netherlands a recent lawsuit came up about a wheelchair. This chair unintentionally drove off a subway-platform. The driver was badly injured and her insurance company started an investigation with help of an EMC laboratory. They found out that the chair was activated by a field of only a few Volts/meter at a frequency of 1.89 GHz.

The manufacturer of the chair did not accept his responsibility by arguing that his chair did meet the relevant product standard for wheelchairs. The radiated susceptibility test in this standard however did not go beyond 1 GHz. The judge decided that the manufacturer could have known that 1.89 GHz was a commonly applied frequency for the digital telephone network.

The manufacturer was sentenced because he had put an unsafe product on the market. It should be noted that this example is about Product Liability and not about EMC. We also learn from this case that the application of a standard is not a guarantee for being safeguarded from lawsuits.

(From Dick Groot Boerle, Teamleader EMC Laboratory for Thales Nederland B.V., from his paper “EMC and Functional Safety, Impact of IEC 61000-1-2”, the IEEE International EMC Symposium, Minneapolis, August 2002.)

About The Author

Keith Armstrong

After working as an electronic designer, then project manager and design department manager, Keith started Cherry Clough Consultants in 1990 to help companies reduce financial risks and project timescales through the use of proven good EMC engineering practices. Over the last 20 years, Keith has presented many papers, demonstrations, and training courses on good EMC engineering techniques and on EMC for Functional Safety, worldwide, and also written very many articles on these topics. He chairs the IET’s Working Group on EMC for Functional Safety, and is the UK Government’s appointed expert to the IEC committees working on 61000-1-2 (EMC & Functional Safety), 60601-1-2 (EMC for Medical Devices), and 61000-6-7 (Generic standard on EMC & Functional Safety).

Related Posts

Leave a Reply

Your email address will not be published.