Why do you call it a 1/8 wave loading coil? It wouldn't be along the
lines of the flawed "loading coil replaces the missing degrees" concept
would it?

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.

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


A 5/8 monopole's performance is quite senstive to the ground plane
implementation. The behavior of a 5/8 monopole over a perfect ground is
not replicated over real radial systems or car roofs, yet people compare
antennas based on the perfect ground plane environment.

As the length of the radiator is increased beyone a half wave, low angle
gain increaeses until about 0.6 wavelengths when power is shifted into a
developing upper lobe. The optimum length over a perfect ground is
probably just a little less than 5/8, and less still over practical
ground planes.

The other dimension is feedpoint impedance. For a simple series L
matching arrangement, R is a little high and the optimum length is
typically longer than 5/8.

So, for optimum pattern, and low VSWR, a better solution is a tapped base
coil with 0.6 wavelength vertical... but that doesn't play well with the
simplest of mobile antenna bases that provide only one connection to the
screw on antenna.

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.

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.

Thanks Owen for the above over view of the 5/8 wave ground plan.

Cheers

Peter VK6YSF

http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm