Sean O'Hare
CLAIMS that a mobile telephone mast is interfering with key fobs and preventing car owners from locking and unlocking their vehicles in Chalfont St Peter have been refuted by an electronics engineer.
For the last three years, drivers parking their cars in three specific parking bays opposite Budgens on Market Place have found themselves victim of the phenomenom which renders their handheld key fobs useless.
According to Malcolm Birdi of Chalfont Repair Centre, a shop adjacent to one of the notorious parking bays, the signal emitted from a 20m Orange mobile phone mast behind Budgens is to blame for the interference.
However, after reading the story in the Advertiser on Thursday, August 9, Alex Hobbs of Cobraworxshops.com, an Amersham-based electronics company specialising in radio transmitters, came forward to discount Mr Birdi's theory.
He said: "Anyone who thinks it is to do with mobile phone masts is barking up the wrong tree.
"If it was caused by mobile phone masts, this sort of thing would be happening all over the place.
"Mobile phones operate on a frequency around 2000MHz while the car fobs operate on a 440MHz band, which is a 70cm band shared with pagers, intercoms, walky talkies and wireless alarm systems to name but a few.
"Being a licence exempt, shared band, the more wireless stuff that comes onto the market the more saturated it gets.
"The upshot of this is that the car fobs are competing against all these other transmitters operating on 440MHz or below, as a harmonically related multiple of that frequency.
"The electronics in these fobs are cheap and not very good so they suffer from the interference.
"This sort of interference is, however, very localised and wouldn't be difficult to locate.
"If you have a wideband scanner and punch in the frequency of the fob and then walk up and down the stretch of road that is affected, the interefence will increase and decrease the closer and further you get from the source."
Ofcom, the independent regulator and competition authority for the UK communications industries, has offered to locate the source of the interference, providing someone who has been directly affected by the interefence and is happy to disclose their car details calls up.
To help solve the car parking mystery, please call the Spectrum Department of Ofcom on 0207 981 3040 and then The Advertiser on 01753 888 333.
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