),
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.
.....but this is 160, and it behaves much different than 40 meters, let
alone higher bands, so I tend to only comment on the 160 part of things
unless something applies across the board.
>
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). >>
Any model I've tried has always been right when I do things correctly, and
understand the requirements of a band. I've had a lot of experience with
5/8th waves on 160, and taller antennas, and have painfully learned some of
the pitfalls of using models. For example, EZNEC undercalculates low angle
gain because it calculates at a considerable distance from the antenna. I
generally ignore that problem because we don't use groundwave, and after
years and years of operating with various antennas I'm pretty well convinced
exceptionally low wave angles are not very useful.
I can't think of anyone ever, since I first got on 160 in the early 1960's,
who has seen an overall improvement from compressing vertical elevation
pattern much lower than a 3/8th wave provides on 160. Some things come to
mind from history, like the weak signal and poor results of W8LT in 160
contests. Another are the hundreds or thousands of blind AB and ABC tests
with people on 160 I have done. I chose to not use my tall tower as a
vertical on 160 because of those results.
Also, nearly all gain in a stack of a 1/2 wave vertical over a 1/4 wave, or
a 1/4 wave over a 1/4 wave, does NOT come from the stack. Virtually ALL of
the gain comes from the current in the higher element and the earth
reflection. If you build a stack of a 1/2 wave vertical over a 1/4 wave
vertical, and if the 1/4 wave bottome vertical is completely removed, gain
is almost the same.
The lower element mostly serves to suppress the higher angle lobe.
This is why the 5/8th wave is a good analogy. Ignoring getting above local
ground clutter, the 5/8th wave obtains gain from distant ground
"reflection". A stack of a 1/2 over a 1/4 is nothing more than a 5/8th wave
with 1/8th wave more current maximum height, and the current "turned around"
in the lower section so the lower 1/4 wave cancels the higher angle lobe.
There is NOT a significant contribution to field at low angles, or
modification of low angles, by the presence of the lower 1/4 wave.
Pretty much only Hams, or Ham based companies or designers, have such an
overpowering fascination with the 5/8th wave radiator. Most commercial
designs created by designers, those who actually understand radiating
systems, use ~1/2 wave or shorter elements. The 43-foot vertical is an
engineering marvel, just like a new 40-10 meter "groundplane" that has its
roots from the same design source. It is a religious or political figure
more than an actual antenna. As such, people really love it and it does all
sorts of wonderful things. Even if it was killing them, they would follow it
blindly.
Only L. Ron Hubbard could have invented better antennas.
73 Tom
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Topband Reflector
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