>I think, but am not absolutely sure, that the systems for sale (minimum of
>300 UK pounds) operate by a trackside beacon transmitting an infra-red pulse
>that is picked up by a receiver mounted in the car (or vice-versa?) which
>displays the lap time, lap, etc.

The ones used in the USA are based on very-short-range radio.  The antenna
is a line beneath the carpet.

Andy

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