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Old 27-09-2006, 12:23   #31
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Rick, I hate to say it, but your advice is almost dead wrong.

First, no horizontal dipole or inverted vee, especially a shortened one with traps, is going to equal a vertical dipole for low-angle vertical radiation and, therefore, for solid DX contacts. This is not an opinion. It is fact based on both theory and practice over several decades. DX-peditioners often prefer vertical dipoles to multi-element BEAMS, because of their ability to put out most of their power within about 5-10 degrees of the horizon. This cuts down the number of "hops" from the ionosphere, and can result in "gain" up to about 20db! That's right, 20db. Read the voluminous literature.

I certainly agree that a marine antenna system should be optimized for efficient RF propagation. A balun doesn't count for anything in this regard. If you're worried about standing waves on the outside of the coax, just add a ferrite device on the coax or an RF isolator device. But, I haven't found them necessary in using vertical dipoles on many sailboats over the last 35 years.

All dipoles are not created equal. Full-size dipoles are better than shortened dipoles using traps. Single-band, resonant dipoles may have the edge over "multi-band dipoles". Vertical dipoles, demonstrably, have much greater performance on DX paths than do horizontal dipoles or inverted-vees. To realize this performance, you only need to rig the dipole with the lower leg as LOW down as possible. On a sailboat, this means you tie off the lower insulator somewhere near the deck.

I'd challenge anyone to measure the difference, in received signal strength after one or two hops, of a dipole with a balun and one without. There's a bottle of Mt. Gay in it for anyone who can prove there's any significant difference.

Bill
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Old 27-09-2006, 12:33   #32
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Rick,
"BTW, I used HF dipoles positioned horizontally at the masthead,"

Is this on a boat or a ship?? Horizontal whips at the masthead??
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Old 27-09-2006, 12:45   #33
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What I submit regarding small vessel antenna radiators

No small vessel has either a real dipole or a real quarter wave radiator due to the presence of any rigging or other metals within a wavelength at HF wavelengths which bastardises all radiator installations into antennas which have no name. As a result, so-called horizontal as well as so-called vertical radiators on small vessels all have 3-dimensional components otherwise ignored in real-world high-class antenna installations. Such components give rise to good skip characteristics with the largely "horizontal" polarization on small vessels in the real world.

The land-based characters who are the most successful at working the marine nets use rotable horizontal beams. These are the guys who save our butts when the going gets tough, not some guy with a single or several switchable dx antenna.

Such real-world concepts save me from being "almost dead-wrong".

Although unusual, Hellosailer, yes I've used these radiators on 32-40 ft sailboats. I've been in places where other hams have come over to ask me if I could get out to some net when they could not and usually don't use more than 80W input power, usually a lot less.
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Old 27-09-2006, 17:26   #34
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" Such real-world concepts save me from being "almost dead-wrong"."

If so, it's not by much :-))

Don't confuse RADIATION PATTERN with VERTICAL ANGLE OF RADIATION or with VERTICAL POLARIZATION. They're quite different.

A dipole is a dipole is a dipole, whether or not it's surrounded by rigging. In practice almost all antennas are affected by their surroundings, whether on shore or on the water. The fact of being aboard ship doesn't make a vertical dipole any less of a "real dipole" than does one hung from a high tree limb ahore (like my three at home).

Proximity to mast and rigging do, of course, affect horizontal radiation patterns somewhat and, to a lesser extent, vertical radiation patterns. It does not much affect polarization, however. A vertical dipole is vertically polarized, as are virtually all antennas on boats which are verticals. And, has been shown by Greg (in Australia) with his extensive modeling of shipboard antennas, verticals still put out a pretty good horizontal radiation pattern all 'round the horizon, with only minor distortions.

The fact of shore-based stations with big yagis or log periodics (which are horizontally polarized) "saving our bacon" has little or nothing to do with vertical or horizontal polarization. I've been such a "big gun" (with 5-element monoband beams at 65' and a kilowatt linear) and with these have both launched and run maritime mobile nets for several years. The antennas and power run by these stations can be impressive, but have little to do with our conversation here about antennas on sailboats.

Rick, our one point of agreement seems to be the need to optimize antennas on sailboats so that they will put out the best signal obtainable within reason. That has been -- and remains -- my passion for over 30 years, since I published my first article on vertical dipoles in QST.

There remains a lot of bum info out there, which even "experts" are too quick to embrace without question and, more important, without testing and extensive real-world experience. All they hype about external ground plates, wide copper strips, and the like is just one example. Baluns are another. Vertical vs. horizontal polarization is another. These are mildly interesting but almost totally irrelevant (and wrong) contentions.

Bill
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