TopBand: EWEs

[Eric Gustafson Courtesy Account]

Gary and I have been having a little discussion off line.  He
thinks I should post it to the reflector.  So here it is.

Eric

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Date: Sun, 29 Mar 1998 15:38:50 -0700
From: Garry & Yelena <ni6t@best.com>
To: n7cl@mmsi.com
Subject: Re: TopBand: El Nino

Great info, Eric--I think you should share it with the Reflector,
and it certainly fills in a lot of blanks for me. Your
observations about size of the EWE are particularly interesting.

N7CL wrote:
> 
> >Date: Sat, 28 Mar 1998 16:56:54 -0700
> >From: Garry & Yelena <ni6t@best.com>
> >
> >>
> >> >With the EWE in the first few days of dry weather, I was not
> >> >all that impressed !  With heavy rains and better conditions
> >> >they began to "play".
> >>
> >> This agrees well with some EWE antenna modeling I have been
> >> doing.  The EWE, unlike the beverage, does _NOT_ like to be
> >> operated over poor ground.  The EWE works best over perfect
> >> ground.
> >
> >I have long suspected this, based upon the widely varying
> >performance reports from operators who have built EWE's.
> >
> >Example: Larry, NF6S put a couple of them in his tiny backyard
> >in the Livermore Valley in California and raved about them. I
> >now recall that Larry lives in a drained swamp adjacent to the
> >now-defunct FCC monitoring station, where he has excellent
> >ground conductivity.
> >
> >Anecdotal, I know, but it jibes.
> >--
> >Garry Shapiro, NI6T
> >
> 
> It was the huge range of performance reported by people who built
> them that started me modeling the things.  There had to be some
> critical parameter(s) which were not routinely accounted for in
> the literature describing how to build them.
> 
> It turns out that as far as the modeling programs are concerned
> there are three things that strongly influence whether the EWEs
> will work well or not.
> 
> First, and most important, is the earth conductivity under and
> immedaitely near the antenna.  The closer to perfect, the better.
> Modeled Beverages simply go dead when you make the ground under
> them perfect.  This also squares with my field experience with
> Beverages.  But the EWE really wants to be over perfect ground to
> work well.  The beverage is a traveling wave antenna.  The EWE is
> not.  It is more properly thought of as a terminated loop.
> 
> Second, the return connection between the feedpoint ground and
> the load ground should be conductive material.  Do _not_ depend
> on the earth material to provide this return path.  It is
> possible to get an earth connection at both ends that is good
> enough but it is not likely to happen in all cases (or even
> most).  It is not a controlled variable and if the connections
> aren't good enough the system isn't going to work properly.
> Again, it helps to think of it as a loop with one side laying on
> the ground.
> 
> Third, The EWE is size critical.  You can't really make it too
> small until it is so small that the preamp NF dominates the
> system noise.  But the pattern goes useless rapidly beyond a
> certain point when making them larger.  So the trick is to make
> it small enough to play well on the highest band you wish for
> it to cover.  Another advantage in making the EWE smaller is
> that making it smaller brings the phase center closer to the
> ground.  This reduces the size of the ground area that must be
> screened to bring the elevation pattern down to very low
> angles.  On topband, a 1/4 wave vertical needs screening out to
> 3 or 4 wavelengths (2100 feet) to bring the elevation lobe down
> to the 5 degree range.  A 7 foot tall EWE only needs 70 feet or
> so of screening to do this.

(This is from my memory of modeling done long ago.  I'll check
this and report back if it is in gross error. EG)


> 
> The EWE is only mildly sensitive to aspect ratio and wire sizes.
> And these changes can be compensated for by finding the proper
> termination resistance.
> 
> So I imagine that hams who get lucky on all these things, and
> bother to find the correct termination rather than plugging in
> whatever worked for the guy who wrote the article, have a pretty
> good experience with the EWE.  And the others don't.
> 
> 73 Eric  N7CL

-- 
Garry Shapiro, NI6T
160 meters: not a band, but an obsession

------- End of forwarded message -------

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