[TowerTalk] 4-Square Configurations

[Tom Rauch]

> An interesting argument for the elevated radial / ground screen 
> configuration is in ON4UN's book.  The vertical radiators are cut for SSB
> and a stub is switched in and out of the SINGLE elevated radial beneath
> each vertical radiator.  The shorted stubs resonate the system at 3775;
> with the stubs unshorted, the system resonates at 3525.  John, ON4UN,
> states there is some high angle radiation introduced when using this
> configuration.  In Europe, however, this is not so disadvantageous.  Also,
> I've heard/worked John on 80 and his signal seems just fine in the midwest
> on CW and SSB.

The stub could be a coil or a stub, and it could be in either the 
antenna or the ground lead.

Unless you want to give up some signal, I'd use a conventional 
ground at each element.

If you make the element a cage of wires, or a bowtie, bandwidth 
will be much greater. 

> The ground screen I have in mind would be 120 wires on the ground
> radiating from my tower base and extending out for 120 feet.  Wires in the
> ground screen would therefore extend 1/4 wavelength (3.5 MHz) peripheral
> to each vertical radiator.

That's a radial system that would help the tower a lot, but not the 
elements surrounding the tower. The current flow in the earth 
around the verticals extends radially from the verticals.

It seems like it is a big mistake to publish a specialty system in a 
general information text. There is a tendency to overlook the reason 
why that system was made the way it was, and duplicate it.

John was willing to "give up" a bit to have a strong short skip 
signal. In the USA, with stations surrounding you, that might be 
OK if you have extra power and separate receiving antennas. But 
unless you know what you are doing it is a system heading for 
trouble. 

When you use a small elevated system, even over a counterpoise, 
you give up:

1.) Bandwidth

2.) F/B ratio and F/S ratio

3.) Gain

You also incur problems with anything near the radials, because 
they radiate a very strong field. 
 
>   I only want to do this installation once.  The ability to easily switch
> from CW to SSB is very appealing and this seems to be the big advantage of
> the SINGLE elevated radial / ground screen system. 

There is no reason on earth you can't do that with a conventional 
system. Not only that, BW will always be greater because the 
ground system is not resonant. 


73, Tom W8JI
w8ji@contesting.com

--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com