How does a stormscope/strikefinder actually work?

There are two theories about how to determine distance, and there are two
lighning detector companies in the market. Each of them strongly propounds
their theory to be the best.

In either case, the direction is done with an electronic version of the old ADF
goniometer using an e-field sense antenna and an h-field loop antenna.
Combining those two with an appropriate phase shifter gives you a cardioid
pattern with a sharp null. Phase shift until you are in the null and this gives
you heading relative to the loop antenna.

The question is where to look in the spectrum for the noise. In some tests I
did as a very young engineer, we found that the lightning spectrum peaked around
50 kHz. and one of the systems on the market looks very closely around this
frequency. Their algorithms have done a very good job on predicting range by
signal strength averaged over many strikes. Quite accurately.

The other company says that 50 kHz. gives the maximum amount of energy, but that
looking in a rather broad bandwidth gives more accurate results. The actual
number is a trade secret, but my suspicion from the components involved is that
they look in a noise bandwith of a few hundred Hz. but sweep the range from 50
kHz. to somewhere in the 3 MHz. range. As a function of WHAT they hear and
comparing one frequency to another for the same strike, they predict distance.
Quite accurately.

Howzat?

Jim



(Dave Jacobowitz)
shared these priceless pearls of wisdom:




Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com