Topband: Vertical dipoles in the real world

[Tom W8JI]

Tom, in addition to what I said in my first reply, there is one thing that 
did surprise me. As I mentioned, the mast is wood (not metal), so I would 
expect current to be flowing in the feedline.  Which is specifically why I 
put a current balun at the feedpoint.  Now here is the rub, I run 1200 watts 
continuous on RTTY  during contests, so I check the pieces and parts out as 
best I can.  One thing I did was to check for heating in the balun..... 
There was NONE!  That surprised me until I realized that the end feed point 
is not a current point, but a voltage point.  So the fact that there would 
be equal current running down the feedline would seem to be pretty 
meaningless since it is very little current and LOTS of voltage.  >>>>

This is also why adding a balun or choke there often has little effect on 
keeping current off the feedline.

We are voltage feeding the half wave element, and also voltage feeding the 
coax shield and mast. It was years before Cush offered a corrective radial 
kit for the Ringo.

<<<<Remembering that end feed is voltage feed, and that I experienced no 
heating of a current balun at the feedpoint, what would be the significance 
of equal (but very little) current flowing back down the feedline? 
Something doesn't make sense to me here, based on what I have read and what 
you are saying.>>>

The unbreakable law is there must always be a current flowing into a 
counterpoise of some type that equals the current flowing up into the end 
fed antenna. There is no way around that.

What happens, even if the common mode choke had an extremely high impedance, 
is the voltage would simply increase until the required current flowed. This 
is actually why the CFA antenna and the EH antenna "work". While the thing 
they call the antenna is tiny, it excites the feedline or mast with the same 
current as the antenna has. Now they have a 100-foot long antenna they never 
even realized they had.

In systems like this, depending on how the feedline is routed or the mast 
length and feedline length, we can wind up with far more ampere-feet in the 
feedline than we have in the thing we think is the antenna.

This same effect appears even in small counterpoises. A small counterpoise 
has considerable potential to earth, and what we do with connections and 
feedlines (as well as earth and things around earth) can have a large effect 
on results.

This doesn't mean all end-fed antennas won't make contacts and won't make 
people happy. Obviously they do make people happy. This is more of a 
testament to how poor some reference systems are, and how little several dB 
might really mean, than it is to how good some common design ideas are.

I find it fascinating how we ignore 400% variables and spend hours debating 
one percent.  :-)

It isn't just Ham radio where this happens.

73 Tom