[TowerTalk] Parasitic 4-square for 40 meters

[Jim Lux]

The mutual coupling between the  monopoles isn't strongly influenced by the
element ground properties (it's mostly affected by the metal in the air).
However, the element current in a passive array IS affected a lot by the
element resistance.  An increased ground resistance shows up as reduced
current, and as a change in phase of that current.   Imagine looking at the
phase of the current through a series combination of a resistor and
capacitor, as the value of the resistor changes by a 2:1 ratio.

So, a more accurate statement would be that "knowledge of the ground
properties is important in parasitic phased arrays".
And, of course, the ground resistance will have an overall performance
impact (you might not be able to get a "good" null in the desired direction,
just because you can't get enough current in the element).

Modeling is your friend!
It's not a perfect match, but you can simulate many of the effects of
element ground resistance by putting a resistive load in the bottom segment
of the element. At least you can check how sensitive the system is, at the
very least.

Once you have your antennas up.  you could measure the mutual impedances,
and adjust accordingly.  If you have access to a multi-node network modeling
program, you could plug those in.  (I'm working on such a thing in Excel,
for this sort of thing, but it's slow work).


----- Original Message -----
From: "ABowenN4OO" <abowen at nettally.com>
To: "Ron Feutz" <feutz at wctc.net>
Cc: <towertalk at contesting.com>
Sent: Monday, February 21, 2005 4:16 AM
Subject: [TowerTalk] Parasitic 4-square for 40 meters


> I assume that you are speaking of a vertical parasitic array which will
> cover 4 directions.
>
> You will find a discussion of such arrays and the requirements for proper
> operation in ON4UN's, Low Band DXing, Chapter 13, paragraph 3.9. Note that
> the ground radial requirements are quite stringent, which may explain why
> most operators opt for current forced, driven arrays.
>
> Driven arrays are covered in chapter 11 of the same book.
>
> INK N4OO
>