[TowerTalk] Re: towers

[K7GCO@aol.com]

In a message dated 04.04.00 05:42:20 Pacific Daylight Time, n4kg@juno.com 
writes:<<
 
 For lightning protection, shunt feeding a grounded element is the best
 solution.    de  Tom  N4KG  >>

Right on Tom.  Where I'm moving to in SD there is a lot of Lightning and all 
my verticals and beam towers will be shunt fed in indirect manners.  I 
described a few days ago the technique of connecting the shield of the coax 
to the tower about 5' high and the center lead going to the horizontal radial 
and adjusting it to resonance --not the tower.  I will have a choke across 
the feed point also.  I will also use a circuit that broadband the antenna 
that involves a heavy inductor across the feedpoint.  This gives the antenna 
a very low DC path to ground.  Hopefully it will divert most of it to ground 
out there instead of the shack.  The coax will be buried all the way to the 
shack and the shield grounded there before it goes into the shack.  There is 
a technique of using a folded unequal diameter monopole vertical to give say 
300-1000 ohms or even higher Rr and an L network to match it.  The smaller 
diameter conductor has the highest antenna R.   The tower is the largest 
diameter.  This way the radial ground loss resistance it very very small in 
comparison and is insignificant--for a change.  The RF currents are greatly 
reduced also in the small diameter conductors.  One can then add a low 
amperage fuse in series with the lead going to the center lead of the coax.  
I've never seen this very high R feedpoint and low amperage fuse idea 
suggested before for verticals.  I did that back in 1938.  If the fuse ever 
blows on it's own it's easy to change as it's at ground level and I've had to 
replace it at times after a storm.  Find the value of fuse that blows after 
say a very long transmission.  If the vertical antenna R is say 1000 ohms, 
the current is 1 A for 1KW, .3 A for 100W and .1A for 10W.  You will feel 
much better about equipment damage from static electricity charges and other 
jolts with a small fuse in the circuit at the vertical.  For beams on a high 
tower, fuses can be added in the feedline in the shack like in a coax switch. 
 I have a ground switch built in my coax switch also.  I've seen what wind 
blown dust, rain and snow static can do and how to suppress it.  Quads are 
typically quieter in these conditions due to the low resistance DC short of 
the Quad loop across itself and the feedpoint.  The Quad has so many 
advantages that it deserves full recognition whenever deserved.  K7GCO

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