As far as VHF, I know a couple here in town I've seen using arrays
for direction finding. But they used four verticals in a square.
It worked quite well. We had one guy that kept jamming one of the
repeaters, and the user of said array was easily capable of tracking
him down to a shopping center parking lot where the guy was sitting
in his car. I suspect the expression on the jammers face when the
tracker tapped on his window was priceless.
The device in the car used an array of LED's in a cross configuration
if I remember right.
He had the antenna array on the back of his truck. I don't recall the
element spacing.

Likely a Doppler direction-finder, possibly a Ramsey DDF-1 or one of
the others of that sort.

They aren't perfect... definitely subject to errors due to multipath,
and they works best when looking for a relatively clean, non-modulated
carrier. Fun, though... I've used mine on several occasions to locate
sources of QRM or jamming.

I've seen similar 4-vertical arrays on the roofs of some police cars
in my area. I infer that they're used to track down cars which have
had their Lojack locators triggered, after a car theft.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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