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Introduction Importance of understanding the environment. Ground Wave Absorption Reflections Scattering Knife Edge Diffraction Gradient Bending Seashore Bending A vertical interface: A horizontal gradient Density Layer Bending A horizontal interface: A vertical gradient Local Dielectric Bending Multipath Environment Antenna Aperture Defined Large Antenna Response in Multipath Conditions Small Antenna Response in Multipath Conditions Synthetic Aperture Defined The Doppler Antenna at Rest The Doppler Antenna Mobile in Motion A Synthetic Aperture Realized Strengths and Weakness of the Doppler, Summarized The SuperDF Antenna at Rest The SuperDF Antenna Mobile in Motion A Synthetic Aperture Realized Strengths and Weakness of the SuperDF, Summarized Stationary Beam Mobile Beam Strengths and Weakness of the Beam, Summarized
The Importance of Understanding the Environment.
I was once told by an engineer that he knew everything there was to be known about Radio Direction Finding. After a little bit of questioning, it was apparent that he knew next to nothing. (Note: This writer has an MSEE degree, with emphasis on Radio Communications, so he is not speaking from a bias against engineers.)
But its not too hard to see how an inexperienced person with some knowledge about radio might come to the conclusion that RDF is "easy." "After all, you just take a bearing with a beam antenna and plot that on a map. You then go to another location, and do it again. Where the 2 bearings cross, that is where the transmitter is located. Simple!"
If you have been doing any RDF work at VHF or UHF, you KNOW it isn't simple. I sure do. I have been on many a hunt where (at least at first) what I was seeing was very confusing. Not only do the laws of physics conspire against the hunter (which this paper discusses), but also the hider is doing his best to scramble your brains (that's a subject of another paper, "Dirty Tricks"). Its a real Sherlock Holmes adventure. You are presented with a large amount of data, much of which may seem to be contradictory or not make any sense at all, and you must sort it all out. In Real Time. In unfamiliar territory. At night. At freeway speeds. Lots of luck!
Successful RDF boils down to:
Equipment 33% Experience 33% Knowledge 33% Luck 33% TOTAL 132% (Well, at least it seems that way!)
So, if you have been bitten by the T-Hunt bug, you are in for quite an adventure! And part of that adventure is in learning.
This paper is an attempt to answer some of these questions.
"How does the signal REALLY get from point A to point B? What effects it along the way, and how is it effected?"
"What are the characteristics of T-Hunt antennas? The strengths and weaknesses of each? The situations where I would best use each? How does each type interact with its environment"
George Russ Andrews
President
George R. Andrews (Russ, K6BMG)
BMG Engineering, Inc.
9935 Garibaldi Avenue
Temple City, CA
91780, USA
Voice 1(626)285-6963
Fax 1(626)285-1684 (24 hour automatic)
Web: http://members.aol.com/bmgenginc
(1 Jun 1997)
Send E-mail to grandrews@aol.com.
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