[TowerTalk] Dipole Question

Jim Reid jreid@aloha.net
Mon, 24 May 1999 12:53:00 -1000


Suppose a 20 meter,  1/2 wave long dipole is also
1/2 wave above the ground.  Feed point R is somewhere
around 60 to 70 some ohms,  and the radiation pattern is
sort of cardioid,  null off the ends,  max perpendicular
to the wire.  All this,  in the books.

Now,  one side of this dipole is now pulled straight up.
So we have a center fed L,  with 1/4 wave wire going
toward the zenith at a height of 0.75 waves,  the other 
leg is still horizontal with the ground,
with the horizontal leg and the feed point still 1/2
wave above the ground.  Now,  what is the feed point
impedance,  and how has the radiation pattern changed?

Next,   lower the horizontal wire 45 degrees.  Now the far
end of that wire is about 0.32 wavelength above the
ground,  but the feed point remains 1/2 wave high.  What
is the feedpoint impedance now,  and what does the
pattern appear to be.

In either of the cases with one leg going straight up,
is radiation favored in the direction of the horizontal,
or lowered leg,  by much?

Drop the lowered wire straight down now;  the lower end from
the feed point is now 0.25 wave length above ground,
while the upper end is now 0.75 wavelength above ground.  What
is the feedpoint Z,  and what is the radiation pattern?

Really interested in accurate answers to the above,  if that
is possible.  Would have posted question to antennas@
qth.net,  but get the following on a bounce back:

">>> MAIL From:<jreid@leka.aloha.net> 
<<< 571 <jreid@leka.aloha.net>... Mail denied to this domain
554 <antennas@qth.net>... Service unavailable"

I seem to recv all e-mail posted to the antennas reflector,  but
cannot post anything,  wonder why?  BTW,  I don't know where
the "leka" part of the domain comes from,  not in my email
address,  but from antennas it comes back as indicated!

Thanks and 73,
Jim,  KH7M

FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm