Can I clarify how radio interference affects the keyless entry systems in cars such as the Toyota RAV4?

I've just read the item titled "Wave machine", and can provide you with a bit of clarification on the matter. The keyless entry and ignition system in the Toyota RAV4 will probably use a small radio frequency (RF) transmitter in the keyfob and a matching receiver in the vehicle. My Suzuki Swift has a similar RF-based system. The problem arises from the fact that the radio frequency (typically 433.92MHz) used for many of these devices sits smack in the middle of a band that is allocated to several primary and secondary users, including the military and amateur radio operators, who can legitimately transmit high-power signals in the band.

The use of this frequency band for remote entry and similar systems is on an "unprotected" and licence-free basis, i.e. the users of such systems have to accept that their systems might suffer interference from the primary and secondary users who are operating perfectly legitimately in the band, and that the users suffering interference have no rights to redress. The problem is compounded by vehicle manufacturers' apparent insistence on designing receivers for their keyless systems that are simple and cheap to make but don't have adequate ability to reject the high-power signals that the authorised users of the frequency band could be transmitting perfectly legitimately, rather that illegally as stated in the "Wave machine" item. The problem is therefore almost certainly caused by the vehicle receiver's poor RF immunity and interference rejection capabilities rather than by an "illegal" transmitter.

Asked on 21 May 2011 by MD, via email

Answered by Honest John
This might become even more of a problem for visitors to the Olympics in 2010 because the powers that are intending to use the same frequency for Olympic radio transmissions. Happily, one manufacturer to use a different frequency (800MHz) is BMW, which is supplying transport for Olympians.
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