[GreenKeys] Questions on troubleshooting an antenna

[hwhall at compuserve.com]

>
First, the higher the number of radials is OK, up to about 36. After 36 or 
so radials you are throwing money away on copper that gives you little 
additional performance. Most broadcast engineers will tell you that about 95 
percent of the ground current action occurs within 15 feet of the base of a 
vertical antenna, so you are right at the edge when it comes to radial 
length. What you have done should work. An article in a recent issue of QST 
supports the effect of the number and the length of the radials.
>

The larger number of short radials is for a buried groundplane. The QST article
and others conclude that for a groundplane above the ground, the radials should
be resonant length for the band in use, and as few as 3 or 4 will suffice. More
is better but the point of diminishing returns is reached with much fewer than
the buried radial system. It wasn't clear in the original post whether he 
planned to bury them in the final installation.

>
A physically short antenna requires inductance at the base, so the coil is a 
good feature. The trick is to get the right number of turns in the coil for 
the 18 foot pigtail in order to attain resonance.
>

The loading coil can be anywhere in the radiating element but at the base is
the most common and the most convenient if one has to change taps when changing
bands. Center and top loading coils can acheive higher radiation efficiency for
the same coil quality but they are mechanically harder to make & support.

I'd guess that his coil has maybe 150 to 200 turns on it, based on the description.
That is way too many. I have a Bill Orr Handbook design here for 80/40/20/15 meters
that uses a 22 foot element and only 40 turns in the baseloading coil (it's 40 
turns of #16 awg, 2 inches in diameter, spaced at 10 turns per inch). The design can
be used on 10 meters but the coil has to be replaced by a series variable capacitor
(the element is too long).

I've offered to email him the design but have not heard back yet.

Wayne
WB4OGM