[TowerTalk] HF Vertical on tower? RF Spill Over

[K7GCO@aol.com]

In a message dated 7/21/00 6:08:25 AM Pacific Daylight Time, 
jhisson1@columbus.rr.com writes:
<< 
 I have tried to send this a couple of time and it seems to have not gotten
 to the list.  I hope I did not get banned for any reason :)
 
 Anyway, my question is will an HF vertical do any better on a tower than it
 would on a mast 8 to 10' off of the ground?
 
 Thanks!    Jason >>

   The main difference obtained by differences in height will depend on how 
much RF spill over on to the coax shield, mast & tower.  It increases the 
angle of radiation.  I've mounted 1/4 WL verticals on top of yagis using the 
DE as it's ground plane, 1/2 WL verticals with no RF spill over on towers and 
also over yagis.  They work great high off the ground when they don't have 
any RF spill over.  I'd add the donuts (lots of them) at the bottom of the 
and give it a try.  Buy the Palomar RF current meter and measure it before 
and after.  

The differences in signal often obtained when both are relatively high isn't 
from the gain difference of the verticals.

Would you believe that the perfect vertical patterns shown in text books with 
designs that don't prevent RF Spill Over is they are printed on paper and the 
ink is nonconductive?  If book pages were of aluminum foil the patterns would 
not be on the horizon.  That's an absolutely true story--I just made it up.

The first article that addressed RF Spill over was in a 1938 Radio mag.  He 
summed it up perfectly with his diagram of RF Sill Over on to the tower from 
a typical J-Pole vertical (one of the worst) and stating:

"Most verticals are matching devices for the coax to the mast and tower."  

The higher they are the more the tower predominates and the less affect the 
antenna has.  One set of radials doesn't stop it all.  That's why the AEA 
Isopole has the least RF Spill Over.  The 2nd 1/4 WL Sleeve kills it.  The 2m 
Ringo was bad, they tried to clean it up and put the extra decoupling stubs 
in the wrong place.  When you use a vertical without RF Spill Over you will 
have a real antenna experience.  The are not critical in the slightest where 
they are mounted either.  

The last article on RF Spill Over (2 total--very sad) was by Remington Rand 
(a W2) had an article on this in a 52 QST on a 2M sleeve vertical and the 
cure which also increased the gain--how about that?  Big break throughs 
finally correct a bad design.   K7GCO  

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