[TowerTalk] 1/2 wave vertical vs 1/2 wave horizontal dipole

[jim Jarvis]

I wasn't going to comment, but some of the responses have been a bit  
afield,
in my view.   so, here goes:

First,  it depends on height above ground, in both cases.    Higher  
is better,
in general.

Second, it depends on whether you want to work distant DX, or  
stateside stations.
The vertical will favor stations outside 3k miles, while the  
horizontal will favor those
within that radius.   By 'favor',  I mean that on 40m, locals will be  
louder on the horizontal
than the vertical.

As an example, I used to work a VR6 regularly on 40 cw.   By  
regularly, I mean 40-50 times
in a year, over several years, on greyline.  My antennas were a  
dipole @ 50',  and a 40m groundplane
with its base @ 50', and 4 radials drooping down through tree  
branches.    His antenna was a dipole strung
between two buildings, at 100'+.    On my dipole, he was regularly s3  
or s4.  On the vertical, he was regularly
s6 or s7, and sometimes s9.    The locals, by comparison, were 20  
over 9 on the dipole, and s7 on
the vertical.   Huge difference in the ability to hear.

Conclusion:  vertical angle effects are the reason to make the choice.

Third,  how to feed the vertical, and efficiency are factors.

The vertical dipole COULD be end-fed, against a radial screen.   The  
literature indicates that it will not
benefit from that radial screen as much as a 1/4 wave vertical would,  
and that peak earth losses will occur
outside a 1/4 wave radial system.    It could also be fed in the  
center, and elevated, without a ground screen.

In my view, the elevated vertical is preferable, unless you're going  
to copper-plate the earth beneath it,
and assuming you have trees of the proper size.    You can do one of  
two things to manage the feed:
dress the coax away from the antenna horizontally for  some  
distance,  or, use coax for the lower half of the
antenna using a combination of a braid-sleeve on the outside, and RF  
common mode chokes on the feeder.

You can also do a variant... make a 40m groundplane with 3 or 4  
radials, which droop severely, forming a
skirt around the coax.   It should stand off by 1' or more at their  
lower end.  Definitely need an RFC at the
bottom of this one!

In any case, by removing the vertical from earth, you eliminate the  
direct IR losses inherent in the on-ground
series-fed situation.   You will still induce current in the earth  
immediately below the antenna, and this will
depend on how close to earth the bottom of the antenna lies.     
Intuitively, the vertical dipole will have less
loss than a GP configuration, since the null off its end is aimed at  
earth.

In terms of vertical angle beam formation, and what are called  
'pseudo brewster angle' effects, from the
dielectric earth,  when you raise the antenna, the important region  
moves OUT from the antenna, and you
have less ability to control it.   Or no ability to control it.    If  
you're worried about very, very low angle signals,
an onground quarter wave with 120 radials is the way to go.

As a practical matter, though,  I favor halfwave verticals for the  
low bands, where I can make them.
Elevated groundplanes are next in preference, where I can put the  
feedpoint up 1/4 wave.    But they work
respectably with as little as 6-10' radial elevation.  (depends on  
your earth conductivity).

I use common mode chokes on all feedlines, regardless of the  
antenna.   You must, with verticals.

Conclusion:  dipole fed vertical halfwave outperforms series fed  
vertical halfwave, and ground planes of equal heights.

The situation is pretty much the same for 20m.   Dominated by  
vertical arrival angle of signals, and possibly
a bit more volatile in its changes.

N2EA


Jim Jarvis, President
Corporate Coach
The Morse Group, LLC

People-Process-Strategy
Achieving Results in a Changing World
www.themorsegroup.biz	
coach at themorsegroup.biz