RE: Help : RF Keyfob blocked on Driveway

["Ian Davidson" <ian@xxxxxxxxxxxxxxxx>]

Hi

Most keyfobs operate on 433Mhz (I think 433.920 off hand). This is a
heavily used channel for many things. Has as been mention wireless
doorbell and also temperature sensors, outside lights with internal
buzzer etc etc. Any of these items crashing causing the transmitter to
stay on permanently will cause the issue. Another cause is NOT mobile
phone masts but masts with UHF transmitters on them, these can be the
new police tetra masts but also older commercial UHF systems. The final
cause can be a local radio amateur using the 70cm band. The last two
causes are due to the cheap receivers built into the cars, not only do
they receive there own channel but get de-sensed when a very much
stronger signal is being transmitted on a nearby channel. I think a
keyfob is a 10mW device whereby our commercial UHF systems can run 25W
erp a few Mhz away.

A cheap radio scanner that covers UHF would allow you to find most
items. Although the devices are digital they still make a noise on the
scanner and enable you to track it to some degree. In really bad cases
OFCOM may help although they do not have to as it is an unlicensed band.

Regards

Ian D.



-----Original Message-----
From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf
Of noughtomate
Sent: 26 October 2006 15:31
To: Ian
Subject: [ukha_d] Help : RF Keyfob blocked on Driveway

Hi,

Hoping you guys might know a thing or two to help me.

Me and the Mrs. Cars are parked on our drive way.

Once/ Twice a month we find that are key fobs to our cars are rendered
useless. The cars do not respond to open or close using the RF keyfob.

I've eliminated battery and car/fob sync issues and it's abit too co-
incidental it happends to both of our cars at the same time.

I've spoken to the neighbours about the problem, but they've not
experienced any issues.

If I park the car on the road, a house or two away, the cars respond
fine to the keyfob.

I'm convinced there's some kind of RF blocker / interrference in close
vicinity to the house but I really can't think of what it is.

The only bits of outdoor kit I've recently installed in the past year-
and-a-half since I've lived there are a Comfort Alarm system (Alarm
bell faces drive) and a hard-wired CCTV camera which is hardly ever
on. The Alarm Bell has a luminosity detector which I use to automate
my lighting.

I know my neighbour has wireless CCTV - I can pick up his signal. That
aside, I've got the 'usual' RF devices - Harmony 895 (RF switched
off), baby monitor, Bluetooth keyboard and DECT phone.

But I'm not convinced that these could be causing RF interference.

Could anybody advise on how I could narrow down / fix the problem ?

Do keyfobs work at a particulr frequency range, which could clash with
appliances ?

I tried a Maplin RF Detector (http://tinyurl.com/y4x69c) , but it
didn't detect anything.

Any help would be much appreciated.

Many Thanks,

Balraj









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