[TowerTalk] One more ground radial question

[Dinsterdog at aol.com]

Jerry,

What you need to realize is that using an Inverted L, the more radials you 
add, the less ground loss you incur which in-turn, shows the true impedance 
mismatch you have going on between the antenna and feedline.  With the ground wet, 
it's sort of like adding more radials because your ground loss is less over 
moist soil versus dry land. 

Let's just say you kept all things even.  That is, you built an Inverted L, 
added 4 radials, and boom, your SWR is a great match at 1:1.  But then add 
radials and watch what happens.  Your SWR begins to creep up- 

I found this out too one day when I used my 160M inverted L with 4 radials 
and it tuned up just great.  Then I added 60 more radials and my SWR went to 
5:1.  Great mismatch between a very efficient antenna and 50 ohm coax.  I was 
flipping out trying to figure out where the hole in my coax was- Then some top 
banders helped me out- 

To cure the problem, they suggested I purchase a Amidon UNUN (unbalanced to 
unbalanced transformer) that once properly connected inline, brought my SWR 
down to 1.5:1 to whereas weather etc had no effect.  It address the impedance 
mismatch between your antenna and feedline.  My guess is that your Inv L has an 
impedance of around 12.5 ohms.  Invisible with a few radials but very apparent 
over wet ground and/or added radials.

As to the number of radials question, I think 30 - 60 radials will really 
help you but if they are not elevated, just put on as many as you can of what 
ever length and fit them wherever possible.  Once you have your totals, play with 
the UNUN to figure out the match on your antenna and keep out of line your 
tuner.  You WON'T need it unless you want full coverage from 1.8 to 2.0 MHz and 
who needs that? Concentrate in the DX window or tune it for stateside chat, 
but avoid trying to put up a single Inv L for both band segments- - 

The UNUN is placed outside at the feed point.  You just need to put on a 
PL259 from the bottom of the antenna with the hot side going to the center and 
ground out the braid.  Then plug in the feedline to the other side of the UNUN 
whereas your SWR is lowest.

The UNUN is a small box that has three female 259 connections on each side 
allowing for different combinations between the antenna's impedance to match it 
to your coax.

The model I used for years with great success is:

W2FMI-1.78:1-HMMU50

Amidon, Inc
250 Briggs Ave.
Costa Mesa, CA  92626
714-850-4660

This has been my experience.  I'm sure you will get a lot of opinions on this-

73  Paul  N0AH