Storm in a key fob

Storm in a key fobThe Electronics Weekly special report into radio systems covers GSM mobile phones, satellite comms, UMTS third generation mobile standard, and even Zoe Ball’s in there for good measure. Richard Wilson kicks off with a look at the regulatory storm brewing in the licence exempt band around 418MHz
If you get into your car using a remote locking key-fob then read on, the following may be of interest to you.
If you are involved in the design and manufacture of the low power radio systems used by most car manufacturers for their remote locking systems then you are probably already aware of the regulatory storm brewing in the licence exempt band around 418MHz.
“The licence exempt bands are no longer sacrosanct,” says Barry Gillibrand managing director of manufacturer Low Power Radio Solutions. “People are riding rough-shod over the articles of the licence exempt policy.”
The eye of this particular storm seems to have been the RadioCommunications Agency’s (RA’s) decision to licence a 16MHz chunk of radio spectrum around 420MHz for the new pan-European trunked radio services, known as Tetra. The problem at a glance
Dolphin’s Tetra network has frequency allocations from 410 to 430MHz. In tests conducted by the Radiocommunications Agency and Dolphin, interference with some equipment using the licence-exempt 418MHz band has been demonstrated at up to 500m from a basestation transmitting at 25W. Dolphin could have as many as 450 basestations in its national network.
The RAhad little choice. Tetra is a pan-European standard and its 420MHz band was allocated across Europe. The problem in the UK is that the Tetra band sits uncomfortably close to the established licence-exempt band of 418MHz, which has been used by car firms and manufacturers of key-fobs and other similar low power radio security systems for a number of years.
“The real problem is the millions of 418MHz devices already installed in the UK,”says Gillibrand, who claims that the licencing authority, the RA, has been caught on the back-foot over this issue. “They’re getting literally hundreds of letters. They consider it a disaster,” claims Gillibrand.
The problem is only surfacing now as the UK’s first Tetra network is being installed by licensed operator Dolphin. “Overnight Tetra appeared and suddenly low power devices have a large power field strength on their doorsteps,”comments Alan Wood, who is managing director of another low power radio system manufacturer, Wood &Douglas. But Wood, who is also the current secretary of the Low Power Radio Association, which represents manufacturers and users of short range radio devices, is quick to point out that their quarrel is not with Dolphin, but with the RA for allowing the situation to happen in the first place.
“Dolphin have been as helpful as they can be in the siting of their basestations,”says Wood, who helped arrange a forum between the LPRA, the RA and Dolphin last month.
According to the LPRA, Dolphin has also attempted to ensure that there will be at least a 7MHz guard band between its transmissions and 418MHz. However, the LPRA admits the design of some low power receivers is so poor that this may not be enough.
The view of the LPRA is that it would be in-advisable in future to develop 418MHz devices, without significant shielding to protect them from interference. “It is still a legitimate frequency in the UK but in the deregulated environment for licence-free radio devices, there is no protection offered by the RA against interference from other users,” says the LPRA in a statement.
There seem to be two alternatives for low power radio companies. They can improve the design of their 418MHz receivers making them more immune to interference from Tetra signals. The RA has been critical of some low cost radio receiver designs in the past and it would consider any improvement to be a genuine benefit to the frequency situation.
The problem is this would add unwanted cost to what are short-range radio receivers for inherently cheap systems such as burglar alarms and car locks. “The worry is manufacturers will get customer complaints for fixes which they cannot support,”says Wood. “Companies will go bankrupt.”
The second alternative is to redesign low power radio receivers to operate in a higher frequency band. The RAis considering the 433MHz band as an alternative for licence-exempt applications, but in the view of Wood this is still too close to the Tetra band.
The radical proposal is to open up a band at 870MHz. This is clear now but may face a new problem with a proposed second generation Tetra band in the same part of the spectrum. “All that does is push the problem further down the road,” says Wood.
It seems there is no easy answer to the problem. The RA would probably say that given today’s radio technology it should be possible to develop a 418MHz or even 433MHz short-range receiver that is sufficiently narrowband and screened to live happily alongside Tetra systems. And it would be difficult to argue with that, particularly as the RA will point out that not all the receivers it has tested so far failed interference tests.
One thing is certain, Tetra is here to stay so this is an opportunity for our radio designers to demonstrate how truly innovative they can be.


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