At 08:52 AM 9/23/98 -0400, Gary Breed wrote:
? I have also heard that
>extra long BURIED radials (more than 1/2 wave in length) provide an
>improvement in radiated efficiency -- I know of at least one ham
>with an 80-meter vertical who added several 2-wavelength radials
>toward Europe and swears that it made a significant improvement.
>
The classic work of Brown, Lewis and Epstein on radial systems (Proceedings of
the IRE, 1937) concluded that "a ground system consisting of 120 buried
radials, each one-half wave long, is desirable". In fact their results showed
that such a ground system resulted in measured field strengths which were
essentially equal to the theoretical limit and their work has been the basis
for commercial broadcast tower designs ever since. When an improvement is
attributed to even longer radials, the question arises as to improvement
compared to what reference system? Lowered radiation angle is sometimes said
to be produced by long radials. However, when one considers the geometry of
producing low angle radiation, it becomes apparent that the radials would need
to be many, many wavelengths long to be effective in significantly lowering
the
angle, which imposes impractical requirements in most situations at low
frequencies. As a guess, 2-wavelength long radials is probably just at the
point where it starts to make a difference, but a lot of them would be needed
to make much difference. (A large salt water ground plane is probably the
most
effective angle-lowering mechanism).
73, John W1FV
--
FAQ on WWW: http://www.contesting.com/antennaware-faq.html
Submissions: antennaware@contesting.com
Administrative requests: antennaware-REQUEST@contesting.com
Problems: owner-antennaware@contesting.com
|