In a message dated 96-10-02 10:42:20 EDT, you write:
>Whether you think differences of 1 dB or so are worth the trouble of
>installing much more extensive radial systems is a matter of debate.
>For ragchewing across town, I think we would agree it's not. On the
>other hand, when trying to raise 9M2AX or 9V1XQ on Top Band long path,
>I know some of us would kill for that extra dB.
>I hope this information is useful to all.
>73, John W1FV
Thank's John, for the summery of the data in the L.B and E study. It was a
bit of work putting it in that form, but that is more useful than verbal
descriptions.
My goal isn't to run NEC or elevated systems into the ground (pun) or stop
anyone from having fun, but we need to get a little science back into
antennas. Some of the stuff lately is getting pretty far fetched, and gives
people the wrong picture of what happens (like little capacitors drawn from
radials or the antenna to ground).
No one knows exactly how any system will work at all locations, although
measurements here over 4 mS/m average soil closely tracked with L,B and E's
study within fractions of a dB. The L,B and E study applies very well at my
location, and also tracked at WAAM in Ann Arbor, Michigan (~15 mS/m).
At my location, NEC predicted much less loss than actually occured with
elevated radials. NEC also fails to conform with measured data from a
Hagn-Barker study of low dipoles, it's about 5 dB off over soild of very high
conductivity (in Tailand). It was about 4 dB or so off here, and 6 dB off at
a BC station over the same type soil as mine. It's about 3 dB off on
attenuation of current in a 500 foot Beverage. It may be perfect in other
situations, or at different heights, but I'm sure there are cases where
models are absolutely off.
That's still a darn good job in the program. I can't imagine anything working
perfectly as a model for something as complex as electro-magnetic fields (the
primary displacement currents are NOT from little capacitors or "capacitive"
coupling) in earth, especially when the 160 meter skin depth is 40- 50 feet
for poor soil, and even 15 feet with excellent conductivity (of course
current actually penetrates even deeper than the skin depth).
Don't buy into these two to four radial arguments (or even less) without
careful consideration of the lack confirming FS measurements. They might work
in some cases, but on the other hand we KNOW that for 40 years 60 radials (or
more) has worked over good or poor soil.
73 Tom
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