[Towertalk] Grounding an Elevated vertical

Mon, 11 Mar 2002 10:20:15 -0500

THREE sources of loss in a vertical system.

1) loss in the current sink, solved with elevated radials or a dense
radial system.

2) E-plane penetration of the ground and resultant lossy current
immediately below. Solved with moderate DENSE ground screen. The worst
loss is right underneath, so even radials shorter than 1/4 will help.
You're trying to make the ground immediately underneath appear highly
conductive.

3) loss in the FIRST BOUNCE, losing reinforcement (up to 3 db) in the
pattern at far field. This loss is most pronounced at very low angles
because the bounce point is farther away as the angle goes down. 1/4
wave radials give reinforcement at important angles for a
ground-mounted vertical. The reinforcement retreats upward with added
height.

This can be solved by extension of the ground field, though this gets
to be a severe economic problem in a hurry. Again, for elevated
radials the bounce point for a given angle takeoff moves farther away
as height increases. This is elegantly solved by operation on a
saltwater beach, where the reinforcement at very low angles over the
sea is spectacular, with spectacular results.

If one is in an environment with substantial ground clutter, where you
are not going to get that bounce reinforcement in any case (think
urban), then elevation will improve things by getting over the clutter
and allowing lower angle radiation just at all. So this is a highly
situational consideration.

73, Guy.

----- Original Message -----
From: "Tonno Vahk" <tonno.vahk@mail.ee>
To: <towertalk@contesting.com>
Sent: Monday, March 11, 2002 4:48 AM
Subject: Re: [Towertalk] Grounding an Elevated vertical

As far as nobody really reacted to the statement of yours that passive
ground screen under elevated radials is a mistake I would like to
emphasize that it is not. Most of the comments in this thread would
also lead you to a conclusion that by having a vertical elevated some
10 feet off the ground and using a few elevated radials leaves you
hardly exposed to your ground conductivity.

Thus how can you deny that installing a nearly perfect ground screen
under elevated vertical with a few radials frees you from 3-4-5-6 or
whatever DBs of ground loss in the system?

Why not use ground mounted vertical then? Why have all the trouble
with elevating?

4 Reasons for using 1 elevated radial:
1. You can tune the vertical by simply changing the radial length.
2. You can get some directivity in the desired direction (use 2 or
more if you don't want that to cancel the currents!!)
3. You get different and better pattern from ground mounted vertical!
10 feet elevation on 80m gives you much better pattern especially
F/B-wise on higher angles! Model if you don't believe!
4. You can get some horizontal radiation using 1 radial and elevating
by more than 0.05 wl - you might want it for local presence!

I am using full size 80m 4Square elevated 10 feet with 1 elevated
radial per vertical and a passive ground screen of 64 c.a. 1/4 wl
radials per vertical on the ground - it's my ideal system! In the air
tests have given only very good results too.

I tried 4 elevated radials instead of one - did not perform better!
Rather worse patternwise and modelling confirms that.
I tried to connect the ground screen to the vertical  - no change
except in the resonance curve as expected!

I had somebody also telling me that a traditional ground mounted
system would give me much better performance!!!
Better kill that myth right now.

:)
73
Tonno
ES5TV

  ----- Original Message -----
  From: K4IA@aol.com
  To: K4BEV@aol.com
  Cc: towertalk@contesting.com
  Sent: Thursday, March 07, 2002 3:42 PM
  Subject: Re: [Towertalk] Grounding an Elevated vertical

  With all due respect to those who have suggested you create a ground
screen in addition to the elevated radials, I think that is a mistake.

  Your elevated radials are your RF ground and make up the second half
of the antenna.  If you add another RF ground 10 feet below I think
you will throw the antenna off without gaining anything.  For one, the
10 feet of wire to the earth will act as part of your antenna system.
Elevated radials require fewer radial wires and work just fine.  They
don't need any help.  If you feel compelled to improve your
  RF ground add 2 more elevated radials. Cebik seems to think 4-8
elevated radials slightly less than 1/4 wavelength long is all you
need.  Check out his articles at http://www.cebik.com/gp.html and
http://www.cebik.com/gup27.html

  You do need a lightning ground and that is where your idea makes
sense.  Run a #4 wire to the ground rod and wrap the antenna end of it
with electrical tape.  Then tape the taped end to the bottom of your
vertical.  You could try to create your own spark gap by leaving some
of the #4 exposed and have it close to, but not touching the vertical.
Run your coax down the side of the ground wire and tape it to the
ground wire for a foot or so before you take a right angle turn to run
off to the shack.  The theory here is the lightning, looking for the
shortest and straightest path to ground, will jump across the
electrical tape (or the gap) and go straight to ground.  Nothing in
the amateur realm will give complete protection against a direct
strike but it may bleed off a lot of the hit before it travels back to
your house.

  The topic of grounding is a a **hot** one and this post may generate
some strong comments.  That is good.  I don't think my idea will hurt
anything and if you want to try attaching the radials to the ground
wire, you do that to as an experiment.  Let us know how it turns out.

  Radio K4IA
  Craig Buck
  Fredericksburg, Virginia USA
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