Topband: VSWR changes with ground precipitation changes

[Jim Brown]

On Mon, 16 Mar 2009 09:33:17 -0400, Dennis Peterson wrote:

>The radial field is predominately located around the base of the L 
>and the lengths are approximately 36 feet long in a 235 degree 
>plain.  There are two (2) FULL QUARTER WAVE radials that extend out 
>from this field in a Western direct but fold back from the property 
>line back towards the base.

You didn't say how many radials you have, but the change in SWR is 
the result of soil moisture suggests that you don't have very many. 

>Will a ground rod out at the end of the quarter wave radial/s make 
>any significant difference?  

No. It's nothing more than a very expensive lawn staple. 

>The ends of all radials are currently unterminated they just go out
?to their ends and are left to float.  

That's how radials should be installed. 

There are really only a few simple things you need to know about 
radials. 

1) More is better.

2) Longer is better. 

3) Symmetry is nice but not critical.

4) Copper close to the feedpoint is MUCH more important than copper 
FAR from the feedpoint. In other words, if you have a limited length 
of copper, use it for more short radials than a few long ones. 

5) The radials do not relate to the earth electrically. The earth 
just holds them up. 

6) Radials work by intercepting the E/M field from the antenna. The 
current produced by that field is lost in the form of heat if it 
flows in the earth, but the current flowing in the copper produces 
very little heat (loss). 

7) If radials are on the ground, you need a lot of them to intercept 
the field, but they do not resonate. If the radials (and the 
feedpoint) are up in the air, as few as 3 or 4 are needed to 
intercept the field, but they need to be resonant. 

There is are excellent discussions of this in the ARRL Antenna Book 
and ARRL Handbook by N6LF and K3LC. 

73,

Jim K9YC