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[TowerTalk] Half slopers using a tower

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Subject: [TowerTalk] Half slopers using a tower
From: (Tom Rauch)
Date: Tue, 1 Jan 2002 17:37:58 -0500
> Please explain what "5 or more above" implies.....There have been many
> others that have shared some very good results with the HALF SLOPER
> antenna. Sounds to me like this antenna is anything but a "free lunch"
> antenna. Taking the time to understand the functionality of an antenna
> is well worth its weight in gold to me, even if it means a little
> extra experimentation initially.

Modelling is great for that. You can look at where the current is, or 
you can visualize it. Keep in mind there is EXACTLY the same 
current in the shield and the center conductor, unless the feedline 
is radiating like an antenna! What do you think happens with all 
that sloper current exciting the tower??

A simple dipole 1/2 wl high is about as good as we can get for 
minimum work. Unfortunately on 160 the height is a problem, and a 
good vertical generally works better anyway.

With an antenna close to earth (much less than 1/2 wl) and 
especially with vertically polarized antennas, we are kidding 
ourselves if we think we have an efficient system without have a 
good amount of radials below the antenna.

The "free lunch" syndrome is where high efficiency and top-notch 
performance is promised with a "next-to-no-work" system, or in 
some cases a small system. The most profound examples are 
some of the magical compact beams and E-H  or CFA antennas 
that claim to defy all the rules.    
I see I left the dB off after 5.  You can expect a vertical with a good 
ground system to be 5 or more dB better than a system where you 
try to get away without a ground, or get away with a small ground 

Now I admit when you are 20 over nine and on a clear frequency, 
no one will notice the difference for all the extra work. But when 
you are in a pile-up, or when conditions are poor, even 1dB can be 
significant. 5 db is amazing, many or most S meters (low on the 
scale) are only about 1 or 2 dB per "S" unit. It is true they are often 
reasonably close to expected up around S-9 or higher. But 
consider what a couple dB sounds like on a marginal signal!

If you want to work general ragchews, you can get by with almost 
anything. If you want to work people when signals are weak or the 
noise is high, the work is worth it.

My 160 vertical is sometimes 20dB better than my dipole at 300 
feet, and almost never weaker than that very high dipole. A dipole 
at 85 feet is always several dB below the high dipole. When 
conditions are good I can use any antenna, but when they are poor 
the work on the verticals really pays off.
73, Tom W8JI 

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