> From: Steve Narducci <nw9g@netusa1.net>
> Subject: TopBand: Vertical antenna phasing
To: <topband@contesting.com>
> Date: Wed, 16 Jul 97 04:27:55 +0000
> Been looking at the butternut hf-2v with 160 meter add-on. This will cost
> a fortune.
And probably not work very well.
> BTW my 160 m wire inverted L , bent at 95 ft with 4 radials is working!!!
Hi Steve,
The key is in two areas.
One area is keeping the current UNIFORM in the vertical (that
requires top loading) and loading losses minimal (that requires a hat
so you can avoid all coils or lossy stubs).
The other area is in the ground system. Four radials are not enough.
Unless the radials are hundreds of feet in the air, ground losses
will be severe.
With a phased array, ground losses can become even more of a problem.
That's because element currents become higher in many phased arrays.
Absolutely the best phasing advice comes from articles like Roy
Lewallen's stuff in the Antenna Compendium. The stuff you will
read about using a power divider is non-sense. Phased arrays
require equal CURRENT (if the elements are equal sized) not equal
power for maximum F/B ratio. Since element impedances are not equal
in unidirectional arrays, that means the elements require different
power....not the same. Lewallen discusses this in depth, as does
Forest Gherke? K2BT.
I use a phased array where I feed a 40 meter dipole's vertical
feedline (about 90-100 ft vertical) as one element, and a 135 ft
tower as the second element. I get four different patterns and about
20 -30 dB front to back ratio with this system, so the elements can
be quite different and still work (although it's easier if they are
the same).
73, Tom W8JI
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|