Topband: Compromise vertical loading questions

[Yuri Blanarovich]

 On Wed, Jan 29, 2014 at 07:54 AM, Tom W8JI wrote:
 
 > How much I can improve by moving the coil up. What improvement should 
I expect if center loading at about 7 meter? How about moving the coil 
all the way up to the top loading spokes? Is it worth the effort? (the 
pole won’t support much up there).>>>>
>
> The coil does not do much at all to current distribution. The spokes 
> pretty much set the current distribution in the antenna, so moving the 
> coil would have almost no effect.
>
>
> 73 Tom
>

Here we go again, Tom spreading misinformation.
IT IS important where the coil is placed in the loaded antenna.
See the discussion at http://www.k3bu.us/loadingcoils.htm

Also, QEX finally started publishing Barry's, W9UCW articles in QEX 
Jan/Feb 2014 issue describing actual measurements and results of their 
experiments.

Interesting, that Tom admits that there is cos (diminishing) 
distribution of current along the straight wire - radiator, but when you 
roll that wire into a coil - magic - current becomes constant across the 
coiled wire according to Tom.

The suggestion about loading coil placement to improve efficiency of 
(resonant 1/4 wave) antenna (trying to maintain maximum length of 
radiator with highest current) is to place the coil furthest away from 
the feed point. The further we go, impedance along the wire increases 
and number of required turns increase in order to maintain resonance for 
the length of wire, while having high current portion of the radiator 
the longest - stronger radiated field.

My most effective mobile 160m antenna was fender mounted Hustler mast 
with loading coil on the top and loading wire going to the short mast on 
the front bumper of 1972 Buick LeSabre.
 
Yuri, K3BU.us
www.MVmanor.com