Hi Steve and all,
> "Another fact which causes me to believe the radiation angle was high was
> that my
> Beverages (low angle antennas) ceased being as effective as the dipole
> after my sunrise
> for Pacific DX stations. (Bill W4ZV)."
Interesting statement, but a puzzling one.
Beverages are excellent high angle receiving antennas. They WAN'T to be
high angle antennas because of their height and wire orientation. Only
attenuation in the media below the antenna allows them to have ANY low
angle "vertically" polarized sensitivity.
I've noticed Beverage mornings and 4 square mornings, but never any "dipole
moments" except for what might have been one with one booming ZL one
morning right at peak.
> I have a 500' Beverage running west to east. When I first put it up, I
> thought something was wrong with it as stations I worked in the USA were
> often virtually inaudible on it, while they were S5 - S7 on the dipole.
Was that antenna terminated Steve, and how was it terminated and fed? How
high was it, and what was around it? Was it in the clear? Was the
termination verified?
>As
> Bill says, the answer is simply the signals were coming in at very high
> angles.
I wish I knew answers so quickly! Please don't take this personally, but
HOW do you know is "simply the wave angle was very high"? Exactly WHAT
tells you that?
> During the really good NA openings last season, 99% of the signals
> fell into this category.
And WHAT tells you that? How can you measure wave angle, when I can't?
> Note that this is simply how the signals actually arrived here - at what
> angle and polarisation they were actually leaving the other end is
anyone's
> guess - I can't tell, for sure!!!
I'd bet you can't tell for sure what angle they arrive at you location
Steve. I know I can't tell what angle they arrive here, and I can't even
think of a way to measure wave angle!
Let me give some food for thought.........
If I viewed the world through a "filter" passing only horizontal polarity,
my opinion would be everything is at high angles and of horizontal
polarity. The earth and a low horizontal wire is a VERY effective
combination for forming that filter.
> Yuri's point about polarisation changing as it leaves your antenna is
> especially important - as is efficiency. Some of those loud USA signals
> were using verticals, while some were on horizontals. My feeling is that
> everyone I worked had a reasonably efficient (low earth loss) system,
> probably over a fairly wide range of radiation angles.
I suspect that is the exception rather than the norm on 160. People tend to
have small yards, and compromised systems. Antennas are generally jammed in
with other antennas, and who knows what the patterns and efficiencies are.
Most people simply do the best they can.
> Now, onto efficiency. Unless you have good ground or lots of half wave
> radials - or both - it is difficult to get an efficient vertically
polarised
> antenna. Dipoles are an apparently easier option. However, vertical
> antennas over poor soil are inefficent at very low angles, while dipoles
> over poor soil are inefficent at very high angles (see ON4UN's book).
I have no idea what ON4UN claimed, but.........
1.) Verticals are inefficient at ANY angle when used with a poor ground.
There is damn little anyone can do about Fresnel zone problems, since even
1/2 wl radials are nowhere near long enough. All we can really work on is
near field losses in the system, and ground reflection losses that mainly
affect real HIGH angles!
Same with dipoles mounted close to lossy ground. They are inefficient at
ANY angle, and adding a ground only really helps efficiency. HEIGHT is the
thing that affects wave angle, unless you have your antenna over an
exceptional terrain like Antarctica.
> Over perfect ground, a dipole at 1/8 wave might have its peak signal at
90
> degrees, but the signal at 45 degrees is only 3dB down from this... Over
> less than perfect ground, maybe there is almost as good signal at 45
degrees
> from the dipole, as there is at 90 degrees...
Is that so? When Hagn-Barker measured low dipoles in Thailand they didn't
find this effect. 1/8 wl is getting near the point where NEC is poorly
verified, but assuming it fully accurate at that wire height does it model
that way? As I recall, none of my NEC based programs show that. Have you or
others modeled it to be otherwise?
> With my struggles with
> verticals here over a poor earth, producing a signal at 45 degrees that
is a
> mere 3dB down from a full size vertical is something I'd love to be able
to do.
That wave angle won't happen with any kind of efficiency with a vertical,
unless you have a half wave vertical and top load it to produce two
out-of-phase current lobes. I can do that, but now seriously doubt anything
would mean anything to anyone since this who issue is so soundly decided!!
> What I am trying to say is that under some poor ground conditions, a low
> horizontal is a better - more efficient - low to medium angle radiator -
> than a vertical.
I understand where you are coming from Steve and I agree with you, but I
think many conclusions reached on the way to this truism are wrong. I think
the only reason you favor a horizontal is your yard is so small that you
have no choice. Now it could also be your soil is worse than Georgia, which
is about the worse in the USA and that you indeed do have very poor low
angle performance with a vertical even on 160. What IS your soil
conductivity in VK6 Steve?
I suspect the ONLY way a low horizontal (over a typical range of earth
types) could be a more efficient radiator than a vertical of any modest
height would be if the efficiency of the vertical was pathetic. It isn't
that the crappy soil would make the dipole good or the vertical bad at 20
degrees, it's just that the lack of a good ground would murder the vertical
at any angle LESS than it would hurt the dipole.
> We are all operating over less than perfect ground, so our dipoles are
less
> good high angle radiators than we think they are (and better medium angle
> radiators) - and our quarter wave verticals are probably worse low angle
> radiators than we think they are, too.
Actually I think our verticals are BETTER low angle radiators than we think
they are. I think we look at programs that view the antennas at fixed very
LONG distances over flat earth, and assume that pattern represents what
happens at closer distances.
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