[Q] Strikefinder Theory of Operation

I happened to be working a college job for a company (Smythe Research
Associates) in San Diego that had a contract to study lightning back in the
early '60s. From that, Ryan Avionics (somewhere in Ohio) built on our
research and did the original Stormscope and from that, the Strikefinder
folks back in upstate New York did some further refinements.

Smythe found that there was an energy peak somewhere around 50 kHz. from
most lightning. Not ALL lightning, just most. The nice thing about
examining the spectrum surrounding 50 kHz. is that it is quiet. There is
nothing else there. Ryan/Stormscope took advantage of that phenomenon and
centered their detection system on 50 kHz.

Strikefinder took it a step further and said that they wanted to look at ALL
frequencies from below 50 kHz. to well above the broadcast band (and I'm not
sure at all that there isn't a bandstop filter for the broadcast band to
keep you from "detecting" the rockcrusher "clear channel" AM transmitter
when you are close to it). How far is "well above"? That is a very closely
guarded secret from the Strikefinder folks.

The detection system uses the old sense/loop technology from the ADF using a
single E-field "whip" (plate) antenna and the classic crossed-loop H-field
antenna(s) with the expected 90° phase difference between the two. By a
clever digital manipulation of this phase difference, you can tell fairly
precisely the direction of the lightning strike relative to the nose of the
aircraft. Some of the more advanced models of lightning detectors have a
built in magnetic reference so that if the aircraft nose moves, the display
moves along with it.

As to range, there are several methods, some of which depend on the
reflection of that hewmongous pulse of electromagnetic energy from the
surface of the earth bouncing from earth to ionosphere and back again,
creating a double pulse train from each stroke. Again, using digital signal
processing from multiple echoes you can create a "pseudorange" fairly
accurately.

Nearly as accurate, and nowhere as complicated is to "assume" a value for
radiated power from the average lightning stroke and simply do a range
predicated on the peak detected strength of the received lightning pulse.
Some will be stronger and some will be weaker, which is why all of them
don't fall directly on top of one another but form a circular pattern
perhaps twenty miles in diameter on the display. Again, microprocessors can
massage the data to toss out the responses at the one-sigma point and only
give those responses that fall in the expected range.

Now as to the practicality. I've flown a Strikefinder for almost a thousand
hours. It has YET to give me a false indication and it has YET to give me
an incorrect bearing and distance (within expected error) on a really nasty
set of cells.

Google "storm detection" and "73 magazine". Wayne Green's bunch of bandits
came up with some pretty simple and accurate ways of detecting lightning
that the average ham could build and use with an XY oscilloscope display.

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford



wrote in message
ps.com...
Group-

I'm curious how Strikefinder technology works. Yes, I know some of
the basics, but what's curious to me is the ability of this device to
estimate range and direction to/from a lightning strike.

What I know thus far is the following:

1. Lightning is nature's version of an impulse function (time
domain), and thus it has wide bandwidth (frequency domain).
2. Strikefinder technology originated, I think, because it was
observed that lightning strikes showed up as noise in ADF units.
3. Strikefinder technology operates, I think, as a specialized AM
receiver that attempts to interpret energy bursts as lightning
strikes.

O.K., now I'm getting on the fringe of my knowledge. Yes, I'm an
electrical engineer, so don't be afraid to dive deep into details. I
just hadn't considered theory of lightning detection before and
curiosity is getting to me. I'm wondering:

1. How does Strikefinder technology estimate range and direction to a
lightning strike (my original question)?
2. If Strikefinder technology operates in the AM band, why?
(Lightning contains many other frequency components from which to
choose.)
3. How are range and direction to/from lightning strikes determined?
(I know that up to around 1/2 wavelength, E and H fields are not in
phase. Does the Strikefinder use "Near Field" characteristics to
estimate range?)

Thank you in advance for your input.

-David