On Fri, 09 May 2008 12:16:14 -0500, K4SAV wrote:
>Yes the SWR is
>high, which is the reason long feedlines can have a lot of loss
>especially on 160 where the real part of the impedance is very
Yes, long lines CAN have a lot of loss, but they often don't,
because 1) the SWR isn't high enough; 2) the line isn't long
enough; and 3) a low loss coax is used.
Example: the vertical I use on 160 and 80 is right outside my
shack, so the feedline (RG8) is only about 30 ft long. Even when
the SWR is VERY high (on 80), the losses are still quite small.
The major losses in most ham verticals are 1) loading
coils/traps/etc. to make the antenna work on a lot of bands; 2) a
poor radial system, either because the antenna mfr downplays the
importance of radials to sell more antennas, or because the ham is
lazy, or because the QTH makes radials difficult/impossible.
Also, remember that dipoles have an inherent advantage over
verticals of 6 dB of directivity in their favored direction, and
help from earth reflection that varies with height. Verticals
don't get much help from an earth reflection unless the ground
conductivity is quite good (i.e., sea water or close) in the far
field of the antenna.
Don't get me wrong -- a GOOD vertical (including the radial
system) can outperform a low dipole at low angles, but the higher
the dipole (as a fraction of a wavelength) the less that
difference is. But most ham verticals are NOT good verticals.
Jim Brown K9YC
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