When ding dongs go wrong.

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When ding dongs go wrong.

Postby m0lsx » Sun Aug 20, 2017 8:47 am

I found this on Southgate ARC's site..

When Wendy Macbean discovered customers at her gym in Londonderry were unable to lock or unlock their car doors she called Ofcom

Ofcom took the call on a Friday and responded on the Monday by sending two engineers Stuart Lannie and Robert Barfoot from the Spectrum Management Centre in Baldock, Hertfordshire, to Londonderry, NI to investigate.

Ofcom describe the investigation on their website:

Wendy told our engineers how customers at her gym and other nearby businesses had, on and off, for nearly two weeks been unable to lock and unlock their cars. One older woman had become quite distressed when she was locked out of her car for more than an hour, while Wendy had resorted to not locking hers any more.

Our engineers broke out their spectrum analyser – a clever piece of kit that scans the airwaves and detects anything out of the ordinary. On this occasion it didn’t, but they asked Wendy to keep a log. Sure enough, the problem reoccurred and Stuart and Robert went back to Londonderry the following Monday and were more successful.

Again, using their trusty spectrum analyser, they traced the problem to a particular bit of the electro-magnetic spectrum – 433.92 MHz. This is a licence-exempt part of the Ultra High Frequency (UHF) spectrum known as the short-range device frequency. [This is also an Amateur Radio band and an inappropriate place to put critical devices like car key fobs]

And the kind of devices that use it are things like car key fobs, oil watchmen (that tell you when your heating oil is running low), and remote controls used by building site crane operators.

“For the most part, these devices are only used in short bursts,” explains Robert.

“The problem comes when one of these becomes faulty and they remain on permanently. When that happens, they can interfere with other nearby devices, like car key fobs, using those same radio waves, which is what happened here.”

They traced the problem to premises nearby. Once inside, they quickly found the cause of the problem – a faulty wireless doorbell. It was switched off and normal service was resumed for motorists out on the street.


You would expect a regulator to tightly define the performance characteristics of both the transmitter and receiver in licence exempt devices such as car key fobs. Unfortunately the UK has failed to do so for the key fob receivers. This has resulted in very poor designs being used which can fail to operate in the presence of strong signals from licenced radio services even if they are operating several MHz away.

It remains a mystery why Ofcom are not working with international partners to get car key fobs moved to a more appropriate part of the radio spectrum. The folly of using 433.920 MHz was pointed out to the UK Regulator in the 1990's. It is particularly easy to jam the key fobs or even steal the car
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Re: When ding dongs go wrong.

Postby alpha_india » Sun Aug 20, 2017 1:19 pm

We're still waiting many of the harmonised standards under the Radio Equipment Directive to be published.
https://portal.etsi.org/webapp/WorkProg ... isplay=ALL

Will OFCOM regulate these or will this be another burden added to Trading Standards?
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