I have been told by others, (treat as hearsay), that for AM broadcasts the 5/8
wave produces a pattern with destructive interference between skywave and
groundwave at medium distances at revenue-important times of day e.g. "Drive
time".
Tim N3QE
----- Original Message -----
From: Charlie Cunningham [mailto:charlie-cunningham@nc.rr.com]
Sent: Sunday, September 08, 2013 11:17 AM
To: 'James Rodenkirch' <rodenkirch_llc@msn.com>; 'Mike Armstrong'
<armstrmj@aol.com>; 'Tom W8JI' <w8ji@w8ji.com>
Cc: topband@contesting.com <topband@contesting.com>
Subject: Re: Topband: 5/8 wavelength vertical is mo betta than shorter
versions??
Jim, Mike et al:
I've been putting together a document along with some models, plots etc.
that addresses the 1/4, 1/2, 5/8 wave vertical question, and I hope,
illustrates where some of the confusion arises - especially with regard to
the 5/8 wave case. The answers are not so simple in that case, and are
dependent on distance, frequency, time of day, and ionospheric conditions.
Please keep your cool and bear with me. Maybe we can shed some light on this
complex issue, with a little less heat and cussin' and discussin'! I'll post
the document on the reflector as an e-mail attachment.
73,
Charlie, K4OTV
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of James
Rodenkirch
Sent: Sunday, September 08, 2013 11:00 AM
To: Mike Armstrong; Tom W8JI
Cc: topband@contesting.com
Subject: Re: Topband: 5/8 wavelength vertical is mo betta than shorter
versions??
Mike: I apologize if my query came across as an insult!! Mea culpa sent
from out here in the black hole of 160 meter communications - s/w Utah.
I think I said I wasn't doubting your claim and I wasn't questioning your
"conclusions" - just attempting to find some modeling or Measures of
Performance to substantiate it as, lately, I have been seeing/reading of
anecdotal "evidence" and I, for one, am interested in supporting
data/measurements.
I use/employ a 43' vertical on 160 through 17 but can't compare it to a 1/4
wave over the same radial field -- certainly your closeness to the water
may "answer" or provide a reason for your success with a 5/8 over 1/4 so,
with the modeling info I supplied perhaps someone who knows the modeling
apps(s) could do some "investigating" in the form of modeling to answer
that?!?~!
OK?? 72, Jim R. K9JWV
> From: armstrmj@aol.com
> Date: Sun, 8 Sep 2013 07:18:18 -0700
> To: w8ji@w8ji.com
> CC: topband@contesting.com; rodenkirch_llc@msn.com
> Subject: Re: Topband: 5/8 wavelength vertical is mo betta than shorter
versions??
>
> Tom (and James),
> I am well aware that my comments concerning the 5/8ths wave was based upon
subjective/anecdotal evidence. I am in a science (Astrophysics) by
profession..... I do know the difference. HOWEVER, I cannot completely
throw out the simple fact that when I altered my 20 meter omni antenna for
Winlink to the 5/8ths, that I received UNSOLICITED comments from the system
users stating (100 percent of them) that my signal was much improved into
the areas they happened to be sailing. None of those people, not a single
one, knew that I was changing my antenna. The purpose being just that.....
to see if anyone complained or said anything else concerning performance
from THEIR point of view. In reality, THAT is the point when supplying a
service..... What do the USERS think of the performance, not what I think or
what a FS meter says.
>
> Even if I had the equipment to measure the performance and the equipment
says that my signal should be improved, but the Winlink user comes online
and universally states my signal sucks, I will REMOVE that antenna. I know
that isn't likely, but if the modelling software states the signals should
be worse and they are, 100 percent, reported as improved, then there is
something at play that the modelling software isn't taking into
account........
>
> Not arguing, just answering that initial question that from my EXPERIENCE
with that antenna, it works better than the quarter wave at the same
locations I happen to be...... AND ONLY ON 20 meters. I won't speak to any
other band, although I would think it would work there, too, because I have
not put one up for those other bands.
>
> As an aside, alot of folks are using that so-called non-resonant vertical
antenna that is roughly 43 feet tall....... They seem to be having some
success with them on the bands. Physically, they are pretty convenient.....
and on 20 meters, they happen to perform pretty well, judging from user
comments, anyway..... and at that band, it is roughly 5/8 wave in electrical
height. So, again, I find it interesting that actual experience argues with
the modelling software (in MY particular instance). But, again, in my case
IN HAWAII, I had an outstanding location that, for some reason I don't know,
happened to favor the 5/8 by alot more than even the theoretical gain would
indicate. NOBODY would comment, much less 100 percent of commentors, on a
slight gain of 2 db. Heck, that wouldn't be worth the effort. However, I
think you are quite right, Tom..... something else is at play.... ground
clutter (I had some.... loads of tropical trees and plants in the area),
some significa
nt
> ly tall sailboat masts RIGHT ACROSS THE STREET from my house (very
close), etc, etc. Then you consider the seawater ground that was so close
by...... There are many factors to take into account, not much of which does
a modelling software take into account. Undoubtedly the answer is there and
not directly related to antenna gain. I did try elevating it on top of a 40
foot pipe mast and using 8 resonant radials....... it made no difference
except to increase the chances that high winds would knock it down. In
terms of SUBJECTIVE performance and comments, no difference. So, I put it
back on the ground and carried on.
>
> Remembering what the antenna was for, and where it was located, putting up
a horizontal 80 or 90 feet in height simply wasn't possible. The SERVICE I
was providing required OMNI directional capability, so even a dipole would
be unsat in at least 2 directions...... those being the directions an
emergency call would not be heard...... Not a good situation for the given
purpose, right?
>
> I will say that I didn't appreciate the comment concerning how I came to
my conclusions about antenna performance. Insults only prove that one has
run out of reasonable arguments..... and that is ALL it proves. Given that,
this will be my last post here and I am likely removing myself from the
list. Insults are NEVER science...... not now, not ever!
>
> Mike AB7ZU
>
> Kuhi no ka lima, hele no ka maka
>
> On Sep 7, 2013, at 18:59, "Tom W8JI" <w8ji@w8ji.com> wrote:
>
> >> The above modeling results just don't support that contention/posit so
I'm wondering what else comes in to play that could lead folks to love the
5/8 wavelength vertical over a shorter version, regardless of frequency? I
don't see one performance comparison that supports that claim. I'm not
saying the "claiming person" isn't correct but....I don't see how!
> >> Help - what am I missing here?
> >> 72, Jim Rodenkirch K9JWV
> >
> > The 5/8th wave obtains the small amount of gain it has through effects
of ground reflection. The current maximum is elevated, and that elevation
causes additional phase shift with the illumination of earth out some
distance from the antenna. The re-radiation of earth is sometimes explained
by an "image antenna". The image antenna is a fictitious antenna directly
below the real antenna, and this "image antenna" simply represents what the
earth at a distance does from the illumination from the main antenna.
> >
> > The 5/8th wave moves the current maximum slightly higher than a quarter
wave above earth, so the fictitious image moves slightly lower than a 1/4
wave below surface.
> >
> > If you move the 5/8th wave above earth, such as in a groundplane well
above the earth, the extra length no longer provides gain. Instead, it
actually reduces gain at low angles.
> >
> > Another effect is the extra height above ground of the high current area
can help get the antenna's main radiating area a little bit higher above
ground clutter.
> >
> > This would also apply to an extended double zepp, where the second
antenna half makes the image unnecessary. Each half of the double zepp is
the image of the other side, so we don't need earth.
> >
> > So it is a very specific benefit from the 5/8th wave caused by moving
the current height up above a reflecting surface, or in the case of a double
zepp moving current away from a second identical element while still having
a common center feedpoint.
> >
> > One of the biggest antenna hoaxes played on people was the 5/8th wave CB
groundplane antenna. Two meter 5/8th wave groundplanes are the same. The
work on the broadcast band to increase groundwave signal because soil is
often reasonably low loss on the AM BCB. If the soil out some distance from
the antenna is lossy, or if it does not exist, the 5/8th length causes
increased low angle loss.
> >
> > This is why when you look at models, outside of specific cases like some
cases of low broadcast band use, we have a tough time seeing the gain
imagined or claimed. A field strength meter has an equally difficult time.
:)
> >
> > 73 Tom
> > _________________
> > Topband Reflector
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