"Peter" wrote in
:

....
I referred to the 1/8 wave loading coil without really thinking about
it. I was unsure of the loading coil dimensions, so I simple tried a
1/8 wave length wire formed into a coil. This is for the simple series
arrangement 5/8 radiator. This created a load coil that appeared to
have a little too much L so I have removed one turn, seems to load up
ok after a little trimming of the radiator. Keen to hear how too
determine the value/dimensions for the loading coil.


Hi Peter,

One theoretical method is to model the antenna, and find the feedpoint
impedance. The R component decreases as length increases from a half wave
to three quarter wave, and X increases towards zero.

Best pattern is closer to a half wave, but R is very high. At 0.7
wavelengths, R is low enough for an acceptable match by using a series
inductor, and reactance will be a few hundred ohms give or take depending
on length.

Having said that I'm not sure what so wrong with missing degrees"
concept.

For one thing, if a certain inductance is required, the quantity of wire
needed depends on several underlying coil parameters.


....

My current 5/8 wave ground plan project is simply to get something on
air, however I plans to construct an improved version with the tapped
coil approach.

That lets you shorten it for a bit more gain, and a good match.

If you cut the vertical for 0.6 wavelengths, you should think of starting
with an inductor with reactance towards 1000 ohms.


I may be looking in the wrong places, but I have been surprised at how
little information there is on the net regarding 5/8 wave ground plan.

Probably displaced by OTS 4 band verticals.

Have fun.

Owen