Topband: 160 metre vertical with 'top loading'

[k3bu at optimum.net]

Thanks Dan,

http://n3ox.net/files/nf.jpg

this is the best visualization of what is happening on typical loaded antenna and that was the whole subject of controversy. 
The other camp and theoreticians were trying to "prove" that the RF current going into the coil is the same as coming out. 
Thanks to "our team" arguments, EZNEC is now able to model effect of decent size coil as shown in your JPG. 
This was the point we tried to bring and correct some misconceptions floating on the web.
Fine tuning can improve the efficiency of designs, but the main effect has to be considered.
Now by comparing areas under the current curve, one can easily visualize and predict the efficiency of antenna. Is there formula that can capture this?

73 Yuri, K3BU.us

now how can the current fly above the coil? (jus' kidding :-)

----- Original Message -----
From: Dan Zimmerman N3OX 
Date: Wednesday, April 27, 2011 9:43 am
Subject: Re: Topband: 160 metre vertical with 'top loading'
To: topband 

> I made a plot this evening that might be of some interest. It <BR>> started with
> an EZNEC model (pretty sure one that originated with W5DXP) of a 
> loadedantenna that shows a clear, large current taper. 
> There's only about half
> the current at the top of the coil as at the bottom. The 
> antenna is an
> eight foot high 40m bugcatcher type antenna with a large (1 foot 
> high, six
> inch diameter) coil. I used EZNEC to generate a near field 
> table of
> electric field values and plotted the magnitude of the electric 
> field with a
> logarithmic** color scale:
> 
> http://n3ox.net/files/nf.jpg
>