From: "Barry L. Ornitz" <ornitz+U@dpnet.net>
Subject: Re: Boltek Lightning detector
Date: 14 Apr 1999
Newsgroups: sci.electronics.design

Dave VanHorn wrote in message ...
>There's a device, at http://www.boltek.com  that purports to be able to tell
>range and bearing to lightning strikes, very interesting, and I'm thinking
>of reccomending our local EOC director to get one, but:
>
>How the hell does it work? (My skeptic alarm is going off!)


I suspect this is a variation on the scheme used in the Raytheon
Storm-Scope unit for aircraft.
The unit does use a set of direction finding antennas, so bearing
information is easy.  To get distance, they rely on the fact that a
lightning discharge is a broadband RF generator.  The low frequency energy
has a significant ground-wave radio propagation associated with it.  At
higher frequencies, the ground-wave is greatly attenuated.  By measuring
the pulse amplitude at two different frequencies, one at HF and the other
at LF, algorithms based on the ratio of the amplitudes can be used to
predict distance.

        Barry L. Ornitz     WA4VZQ     ornitz@dpnet.net