Topband: GAP Vertical Question

[Tom W8JI]

>> But feeding a half wave vertical with the base near the  ground
> > still  results in substantial ground losses without a radial system.
>
>> Don k4kyv
>
> And this statement is based on what?  Publications, measurements,
> modeling?
>
> I have built a number of 1/2 wave verticals without radials and compared 
> them to 1/4 wave verticals with radials.  They are
> indistinguishable in performance and certainly do not exhibit
> substantial ground losses AFAIK.  The PAR electronics 1/2 wave
> end fed antenna seems to have a good reputation, unlike some
> GAP verticals.

I know you already know this Rick, but everyone else should be reminded 
***EVERY*** end fed antenna requires some type of ground system. In the PAR 
antenna, the coax shield is a "counterpoise", just like in the end-fed Zepp 
the ladder line is a counterpoise that radiates.

While some seem to have created a new physics that a simple single wire 
counterpoise can be non-radiating, there always has to be some fairly strong 
external induction field associated with end feeding an antenna. It can be 
predominately electric or magnetic, but rest assured there is a return path 
providing that second terminal for the feedpoint.

The PAR antenna gets away with a sloppy feed system because most users run 
low power, and the shield of the coax becomes the counterpoise.

In the real world loss can be all over the place depending on the exact 
system, including feedline length and grounding. While it is true that I^2 R 
feedpoint losses are not nearly as bad as a quarter wave Marconi, we 
exchange the strong current issues of a high current feed with high voltages 
and a strong electric field. This is why the end-fed Zepp, even in perfect 
construction form, has terrible local RFI issues even though feeder EM 
radiation is minimal.

If you do a near field measurement of a perfect Zepp, the electric field 
intensity is off the charts around the feeder. If the feeder is the wrong 
grounding for common mode, the common mode current can be terrible and the 
electric field greatly drops. The feeder can radiate as much as the antenna, 
or more, with a simple ground change! This also applies to the PAR.

Even with a half-wave, we have to have some common sense about what we do at 
the feedpoint and feedline. There are still displacement currents, and if we 
get rid of that pesky ground current we do that by trading for a pesky 
electric field. :-)

There are enough well-spoken salesmen selling people magic, and they don't 
need our help.  :-)

73 Tom