At 10:42 AM 7/26/2005, Bob Kellow, W5LT wrote:
>Seems like this problem should be an easy one to model with AO or similar
>modeling program.
>Tell the program the antenna is in free space, then define the antenna and
>then the screen in the Z-lane below it. The diagonal version would be
>easiest to model. Anyone want to give it a try?
>73s
>Bob, W5LT
The trick is in adequately modeling the earth losses. Wires close to the
ground are always challenging to model, and small changes in the spacing
(from earth) or the dielectric properties of the soil can change things a
lot. And, then, once you're done, you'll have a pile of model data that is
hard to relate to actual use. As you say, it would be pretty straight
forward (although time consuming) to iterate over some ranges of spacings,
lengths of wires (or zig zags) and soil properties.
On the other hand, if you set up in a field, and do a couple dozen tests
with various arrangements, you'll not only get the RF data (which could be
used to validate the computer modeling results) but you'll also get that
invaluable data on how long it takes to lay out the wires in various
patterns, etc.
In the context of a potential QST article, too, it would be a pleasant
change to see both the model data AND actual field test results with
halfway decent experiment design. It would be fairly easy to get actual
quantitative results (as in dB differences) instead of a "I worked umpty
ump countries with a model X transceiver at some unspecified time and date"
or a "it sounds loud" or "it's full quieting into the repeater". The NVIS
path is moderately stable (compared to, for instance, a DX beacon with
multiple hops and traversing many different ionospheric conditions along
the way).
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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