[TowerTalk] Vertcal Dipole

[Tower (K8RI)]

K0PYK wrote:

>Tower Talk'ers,
>Has any made a vertical dipole (lets say for 20
>meters) where it is end fed with coax. I will try and
>explain my thoughts;
>  
>

Yes, but it was quite some time ago.  When using the braid for the 
bottom half they make a very good portable antenna that can be hung from 
a tree branch.

>* top half of radiator, i.e., 1/2 of dipole is a
>single 14 guage wire.
>* bottom half of dipole would be coax...the center
>conductor would feed the top half inside the braid.
>* the bottom half of vertical dipole would be the
>outside braid of the coax.
>  
>
I'm hearing your question a bit different than others.

This sounds like a center fed half wave with the feed coming up through 
the bottom half of the dipole.  A common way of building one of these 
for higher frequencies is to strip the jacket back far enough that a 1/4 
wave length of braid can be pulled back over the jacket.  You have to 
strip the jacket back quite a bit more than a quarter wave as the braid 
gets a lot shorter when expanded.  This also forms an open 1/4 wave stub 
where the coax comes out.  I've never seen any decoupling used due to 
the configuration.  Think of an Isopole (TM), but used at 20 meters and 
the the shield takes the place of the top cone.


>* the bottom half of the dipole would be fed from the
>bottom and end where the top half starts.
>* a decoupling device may be needed at the bottom of
>the dipole...1-1 balun???.
>* I realize that normally dipoles are fed in the
>center.
>  
>

As is this one. It's just the coax doesn't come in from the side, but 
rather up through the bottom 1/4 wave.

>* A person could use some type of tubing for the
>bottom half and still feed it in the center, but I was
>looking for something that would be portable and you
>could just hang up vertically or horizontally.
>  
>
These used to be listed in the ARRL Handbook and the antenna hand book, 
but I don't find on in either of the latest ones.  I haven't searched 
the older handbooks yet.

Good Luck,


>I look forward to your thoughts.
>Thanks in advance,
>Tom, K0PYK 
>  
>

-- 
Roger Halstead (K8RI ARRL Life Member)
Worlds Oldest Debonair (N833R S# CD-2)
www.rogerhalstead.com