[TowerTalk] Improving my dipole

[Jim Lux]

At 06:33 PM 6/27/2005, Art Boyars wrote:
>On the CQ-Contest Reflector K7QQ said: "You have to keep in mind that the 
>best antenna doesn't exist. You can only get up what you can and it is 
>never enough."  Well that's where I am, but I'd like advice from you 
>experts on how to improve my antenna, within my personal constraints.
><snip>

<snip>

>I've pulled the ends of the dipole as far as I can into the trees (maybe 
>too far), but it still sags quite a bit -- 5 to 10 feet, by eye.  Some of 
>the sag is probably from the weight of the antenna wire and the feedline, 
>but I think a lot of it is simply from the dipole's being longer than the 
>span between the trees.

Doesn't take much weight in the middle to pull it down, even with thousands 
of pounds of tension.  It's that 1/sin(theta) thing.

>I have two seat-of-the-pants concerns.  First, I may be getting losses 
>from having the ends of the dipole in the foliage.  Second, the vertical-V 
>might be more NVIS-like than Iis good for me.  Obvious solution is to 
>shorten the dipole a bit, but that would make it even shorter than the 
>recommended 100-ft minimum.  So, first question for the experts:  Do you 
>think I'll do better to shorten it, or should I leave the ends in the trees?

My own experience has been that keeping the ends out of the trees, and 
using a tuner to compensate for the non-resonant length, has been 
better.  The ends of the dipole are a high voltage point, and aside from 
the arcing problem, the high voltage leads to higher losses in the leaves.

>Second-order solution and question:  If it turns out that the feed line is 
>weighing down the center, would I be better off to let it sag than to 
>change to something more like TV twin-lead?  (I recall some discussion 
>here about Radio Shack selling a twin-lead with heavier-than-typical 
>conductors.)

Let it sag... the radiation properties aren't all that much different 
between a dipole with the angle being 120 degrees between the wires and 180 
degrees (perfectly flat).  However, if you do happen to have a resonant 
length, 120 degrees included angle will be closer to 50 ohms than perfectly 
straight (which has an impedance of 72 ohms).



>Thanks for your help.
>
>73, Art K3KU