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Re: [TowerTalk] Dipole fed with balanced line?

To: "Ken" <>, "Steve Hunt" <>
Subject: Re: [TowerTalk] Dipole fed with balanced line?
From: "Gene Fuller" <>
Date: Tue, 17 Jan 2012 11:06:54 -0500
List-post: <">>
Regarding "dipoles" there are a number of points that have been well 

1. If the antenna is to be used for multiple bands, keep  it nonresonant to 
avoid feed point impedance extremes.
2. Shortened "half wave" antennas can still be quite efficient. e.g. 45-50 
foot loaded elements on 40 meter yagis.
3.With a multiband dipole where higher SWR's are likely,  by the time you 
get up to 10m low loss  line can save appreciable power loss.  Open wire, 
ladder line, foam filled, even good quality 300 ohm TV line(for lower 
power), are all possibilities.
4. "Off center fed" antennas may allow finding good compromise feed 
impedance point but balanced antennas have the benefit of relatively 
nonradiating feedline.
5. A good "antenna tuner" is a great station asset. It's a virtual necessity 
for multiband dipoles and allows full band coverage with single band 
6. For low angle/DX work try to get as much current as high as  possible. 
Letting the end 10%- 20%  drop vertically to get a total length that gives a 
good feed point impedance will not effect the gain drastically. Remember 
that the end of the antenna is essentially an open circuit and not much 
current flows through an open circuit.
7. A level, multiband, horizontal dipole, used at a frequency where it is 
much more than a halfwave long will have increasingly nice gain but will 
have increasing narrow lobes and then  develop directional lobes. If 
possible consider a second dipole horizontally rotated by 45-90 degrees to 
help fill in the notches.
8. There is no magic about a wire antenna being resonant if you're not 
trying to match a feedline to it.
9. On top of all of these points are overlaid the practical considerations 
of available real estate, supports, and finances.

Just to throw another log on the fire, don't forget about vertical dipoles - 
effecient with no radials, low radiation angle, swap height for 

So, What kind of antenna should you put up and how should you fee it ?   It 
all depends..................................... but have some fun at it !

Gene / W2LU


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