Towertalk
[Top] [All Lists]

[TowerTalk] Re: Radials over salt water

To: <towertalk@contesting.com>
Subject: [TowerTalk] Re: Radials over salt water
From: W8JI@contesting.com (Tom Rauch)
Date: Wed, 10 Jan 2001 06:18:48 -0500
> The following morning after the storm had passed, we started making
> feedpoint measurements to determine why the SWR on each vertical was so
> much higher than back home.  Imagine our surprise at finding the feedpoint
> Z of each vertical reading 40 ohms instead of 6 ohms!  We then started
> laying out short radials, about 10 feet long, to augment our 16 long
> radials that had been previously layed out.  After laying out a total of
> fifty radials per vertical, the feedpoint Z for each antenna was close to
> the expected 6 ohms.
> 
> Many lessons were learned that weekend, but most importantly:
> 
> 1) Substantial ground losses can occur near salt water unless a
> sufficient number of radials are used extending from the base of a
> quarter wave (or shorter) vertical.  This can be readily determined by
> using an antenna analyzer or noise bridge.  Running a few radials into the
> salt water doesn't get the job done if the base of the vertical isn't VERY
> close to the waterline.

It won't get the job done even if the base of the antenna is OVER 
the salt water.

Salt water is not copper. It is a few hundred times better than good dirt, 
that's all.
  
> 2) The lowering of the takoff angle near salt water can make an
> astounding difference in the ability to work DX, especially with QRP
> power levels.  From the beach, 80M was alive with EU DX, and we worked
> almost everyone we heard with QRP power levels.

Maybe, maybe not. What were conditions like at that SAME 
moment back at the other QTH?
 
> 3) Phased arrays for the higher bands (10, 15, 20M) can be made to
> utilize half wave base fed elements to virtually eliminate ground loss and
> to negate the need for radials if located right at the salt water line. 
> (I know some of you are gonna' beat me up for that one-HI!, but repeated
> tests from Coastal North Carolina have borne out the efficacy of this
> concept).

If you handle the feed system right, it will work, but 1/4 wl lines 
need to be changed to 1/2 wl lines when phasing voltage fed 
antennas. The entire feed system will be wrong if you use the 
concepts for a normal current fed element, and you can run into 
phase shift problems in matching systems.

> 4) Personal tests comparing inverted vees with verticals near salt water
> have shown substantial (consistent) gain in favor of the verticals. Back
> home 125 miles from the coast, the vees win out every time.  The antenna
> models over salt water vs. average ground bear this out, but it's a lot
> more fun and interesting observing it firsthand.
 
Long term  tests here have show my verticals in Georgia far from 
the coast, with a path to Europe that exits the mainland up around 
the northeast USA and is over land, show my verticals beat dipoles 
at 300 feet on 160 meters.

I have a real radial system, not a few elevated radials. 

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


<Prev in Thread] Current Thread [Next in Thread>