Topband: Compromise vertical loading questions

Tom W8JI w8ji at
Wed Jan 29 07:54:18 EST 2014

How much I can improve by moving the coil up. What improvement should I 
expect if center loading at about 7 meter? How about moving the coil all the 
way up to the top loading spokes? Is it worth the effort? (the pole won’t 
support much up there).>>>>

The coil does not do much at all to current distribution. The spokes pretty 
much set the current distribution in the antenna, so moving the coil would 
have almost no effect.

<<<<My top loading spokes are sloping more than the recommended angle. 
According to the ON4UN Low Band book I got the impression that the 
difference should be minimal when close to salt water. I have tried to slope 
them less, but easily get in trouble with the weak pole in the wind. And 
there are pats to the beach every where so options are few.>>>

The slope of the spokes has virtually  the same effect on current 
distribution over earth as over sea water. The downward slope, in effect, 
shortens the vertical. This is because when folded down the current into the 
spokes opposes current in the vertical, subtracting from effective height. 
The cancelation is a cos function as well as ampere-feet (or ampere-meters), 
so it rapidly becomes worse at smaller angles. It actually deals with EM 
field intensity and direction as the fields from the wires and radiator 
interect at differing angles.

Which one of the two above actions would be the most beneficial? Move the 
loading coil higher up or rearrange the top loading spokes for a better 

The coil would have almost no effect. The loading wires effect would depend 
on angle.

73 Tom

73 de Björn,

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