Mike, could you kindly supply the address on Iroquois Point? If it's in
the area I'm looking at with Google Earth, the answer why the difference is
pretty plain, and points to why such a difference vs. a 160m vertical on
rural terra firma.
73, Guy.
On Fri, Sep 6, 2013 at 1:30 PM, Mike Armstrong <armstrmj@aol.com> wrote:
> Oh, I didn't address one comment you made, Tom...... 5/8ths are dogs on
> 160? Really? That is odd in the extreme to me. I had incredible success
> with a ground mounted 5/8 on 20 meters while I was stationed in Hawaii. I
> was rather space limited, so I could only go up and a tower mounted beam
> was a "no fly zone" in that particular situation. So, I decided to try the
> 5/8ths wave vertical and its performance was nothing short of spectacular
> when compared to a 1/4 under the same circumstances. Not to malign the
> simple 1/4 wave, but the 5/8ths performance improvement went way beyond
> what I would have expected...... and my expectations were certainly
> reasonable. My thinking was that lifting the major current node a bit
> above ground would probably be an improvement and, to my surprise, that was
> an understatement in the extreme.
>
> I wouldn't want to overblow the results, but I simply couldn't believe how
> well the antenna performed on 20. To be sure, I was on Oahu out in
> Iroquois Point housing, which is well situated with regard to the sea (you
> are basically ON the water in almost all directions). Additionally, I had
> 60 radials underneath the thing, spread evenly around the base (in straight
> lines, no bending). So it was definitely an ideal vertical location. But
> the difference between it and the quarter wave was what truly surprised me
> (with all else being the same.... sea water location, number and length of
> radials, etc). To hear that it doesn't translate to 160 is really a
> surprise to me...... Tell me more, assuming you did any kind of study into
> why it didn't seem to work well. I am as interested in why something
> DIDN'T work as I am in why it does..... If for no other reason than to save
> a few bucks and alot of time.... LOL
>
> Mike AB7ZU
>
> Kuhi no ka lima, hele no ka maka
>
> On Sep 6, 2013, at 9:25, "Tom W8JI" <w8ji@w8ji.com> wrote:
>
> >> Fully understood. I wasn't referring to the usual collinear antennas
> sold by "comet" or anything of that nature. I am referring to the stacking
> arrangements used for ops like moonbounce, etc. As far as the design
> theory (and practical application) goes, I have a reasonable amount of
> schooling and experience (been active since 1966..... he he he). Just so
> you realize I am not referring to the often (always?) false gain claims
> made by manufacturers for their antenna designs.
> >
> > ........but this is verticals, and not a narrow BW like a long Yagi. The
> narrower the pattern of a cell in the stack, the wider minimum useful
> stacking distance becomes.
> >
> > Also, for 160, antennas are near earth. Earth spoils everything. A 160
> antenna at 260 feet is like a two meter antenna at 3.25 feet above ground.
> >
> >
> >> All I was saying was, "yes, it is possible and is done" when speaking
> to vertical stacking. As far as stacking what we would call "ground plane"
> antennas (quarter wave vertical element against elevated radials), the only
> example I have seen with any regularity is done aboard some Naval vessels
> (stacked/phased, if you will, horizontally on a yard arm). I "think" I have
> seen the same thing at airports, but I cannot tell for certain that they
> are phased arrays or just happen to "look" like they are related.
> Understand that in all cases to which I refer, including my own, I am
> speaking of phased arrays, which I believe is what we are talking about as
> well. I may have misinterpreted the question to some degree.
> >
> > This is 160. The distance ratio for the same behavior on two meters is
> 80:1. If we look at: http://www.w8ji.com/stacking_broadside_collinear.htm
> >
> > we see **freespace** short dipole stacking distances, between current
> maximums, is 0.35 WL for 1 dB stacking gain. This is for freespace. That
> means the current maximums have to be .35*160 = 56 meters apart **if** the
> elements are in freespace. They have to be even further apart if near
> earth, because the earth reflection already compresses the vertical
> pattern. I'd guess, for 1 dB stacking gain over a ground mounted vertical
> (ignoring ground losses), we could move the lower current maximum to about
> 50 meters above earth and eliminate the upper element. That would pretty
> much be a vertical dipole. If we wanted to get 2-3 dB gain, we'd probably
> need 300 feet of height and an inverted groundplane at the top.
> >
> > For 160, is it is a useless endeavor at normal heights.
> >
> > Making matters worse, 5/8th wave verticals are dogs on 160. Been there,
> done that, used them. A 1/4 wave vertical, or something up to maybe 200
> feet, is actually better. They have never worked well here, they never
> worked when I used broadcast towers, and when W8LT used them in 160
> contests they were also pretty weak.
> >
> > The whole thing is a waste of time on 160. Even if someone could run a
> vertical collinear with useful gain, it would just kill their signal by
> focusing it at too low an angle for 160, while nulling more useful angles.
> >
> > 73 Tom
> >
> >
> _________________
> Topband Reflector
>
_________________
Topband Reflector
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