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Beverage Antennas Construction by Tom, W8JI - part I.

15. listopadu 2006 v 17:19 | Petr, OK1RP |  Antennas
Hi,
everybody who is interested in the serious TOP band operation or even the DXing on that band know that most important is the reception. Althought I am one of the TOP band ops. who have pocket size gardens nor even post stamp size lot for antennas in fixed QTH - sometime I have chance to go to operate portable where is temporarily possible to install antennas for serious operation even for improved reception.
I tried to install many years ago receiving antennas incl. Beverages but many times I had no success nor results as I expected. During that time comes to my head a lot of questions about an installation of the Beverages antenna and construction...which height is enough, does make any impact if wire zigg-zagging on the lot, what about the termination value and his impact for directivity, how to make correctly the transformer and many others.
If You are still not satisfied with Your Beverage or You would like to improve it then read the followed article very carefully as its writen by one of the famous TOP bander Tom, W8JI !
Beverage Antennas Construction
I installed my first Beverage Antenna (in the early 1970's). I was delighted to find a large improvement in weak-signal reception from such a simple, inexpensive antenna. Over the years I've continued to use, compare, and refine my Beverage antennas. Despite having very large vertical arrays, Beverages remain my primary DX receiving antennas. There just isn't any antenna that is as simple, as easy to construct and maintain, and as foolproof as a Beverage!
I refine my antenna systems by comparing systems against each other for extended periods of time, usually more than a year. My station has a convenient switching system allowing instant comparison of antenna systems. When an antenna system is almost never used, I abandon that system and try something else. Even though I use engineering tools (books and models), I always compare and measure actual working systems. I presently have over thirty Beverages in three different clusters of arrays, the end result filtered through years of measurements and A-B testing of systems.
A great much has been written about Beverages. Unfortunately much or most information is a repeat of previously published information (and misinformation) from verbal discussions or from other articles or handbooks! It is time to set aside some of the myths that have been handed down and repeated so much they have become "fact".

Types of Beverage Wire

The most commonly used wire types are single conductor hook-up or electrical, electric fence wire, and special antenna wire such as copperweld. The only significant and easily noticed difference between these commonly used wires is in physical properties, such as ease of soldering, strength, and life

Insulated Wire

Sporadic claims have appeared indicating insulation prevents charged droplets of water from making an antenna "noisy". I've never been able to verify that rumor either in A-B tests of actual antennas or through planned experiments. Other reports, many from reliable sources, also seem to discredit this rumor.
One of my experiments was to charge a stream of water (against earth) with an extremely high voltage supply, and spray the water on a wire. Other than corona noise from sharp points, the type of wire made no difference at all in "noise". The water droplets obviously were not hitting the wire like hundreds of random charged capacitors, they generated no noise at all. This is really what we would expect, if we consider that each drop contains only a very miniscule amount of change and also has nearly perfect insulation (distilled water is a very good insulator).
Controlled observations also tend to support the idea corona, and not charges in individual droplets, cause precipitation static.
In Ohio, my long Beverages stretched across open farm fields. Snow would whip across the fields, rain would pelt the wires, yet insulated and bare wire Beverages running in the same direction always had the same noise level. Beverages that picked-up corona (or "p-static") noise were always near or aimed at tall towers. With corona sizzling at 40-over-nine on my tall towers, Beverages (and even small "magnetic" loop antennas) aimed at the towers would "hear" the same precipitation noise.
The same was true for tower-mounted antennas. The largest noise problems came from antennas mounted high on towers, and generally were with antennas that had "sharp" ends jutting out in the air. Lower antennas, even those of identical construction, were either significantly quieter or totally free of precipitation static. This effect was reported many times by contest operators and DX'ers with stacked antennas. They universally switch to low antennas to eliminate or reduce p-static, even though the same moisture is hitting the lower and upper antennas. This strongly indicates precipitation static is from corona discharge, and not from charges in each individual drop of moisture hitting the antenna.
After my move to Barnesville, Georgia my first antennas were all insulated wire. Hook-up wire was pressed into service in my first group of temporary Beverages. As non-insulated conductors permanent antennas were added, there wasn't any observable change in inclement weather noise. As before, the antennas nearest or aimed at tall towers picked up some p-static noise. Antennas located away from the towers remained free of precipitation static, whether bare or insulated.
There is also some chance, if the antenna wire is not under significant tension, that insulation may sometimes hide a broken conductor.
Insulated wire may reduce leakage currents if a substantial part of the conductor is in contact with resistive paths, such as wet brush or tree branches, but you may be better off trimming back any substantial foliage in contact with the wire.
While insulated wire has no major performance disadvantage, it also has no advantage.

Type of Conductor

Copper wire is a good choice if supports are close. Copper wire lacks the mechanical strength of steel-core wires, but is very easy to work with. It is softer, making it easier to bend. Copper wire can be repeatedly scraped or re-soldered without worries about piercing a thin copper coating and exposing a rust-sensitive steel core, and it is readily available and relatively inexpensive in large quantities.
Copperweld wire is much stronger and has about the same RF resistance as 100% copper. Like copper, it is easy to clean and solder after it has been exposed to the weather as long as you are very careful to not scrape through the thin outer coating of copper. It is considerably more difficult to work with than normal pure copper wires, any kink or sharp bend will substantially weaken the wire.
Most fence wire I've found is cadmium plated, rather than zinc galvanized. Using RF current meters, I have measured increased losses when using zinc or cadmium plated steel wire. Beverages already have substantial current loss due to the close proximity with lossy earth. I've measured about 60% of feed point current remaining (~4.4dB loss) after passing over around 700-feet of electric fence wire, and about 10% more current (~3.1dB loss) using copper-clad steel wire. Steel fence wire would aggravate losses that already limit the benefits of using long Beverage antennas. In a very long antenna, the small additional loss of steel fence wire might slightly reduce performance.
In my Beverages, the important consideration is antenna maintenance. I use copperweld wire or electric fence wire, because strength is a primary concern. With spans exceeding 200 feet, my antennas need a large strength to weight ratio.
Don't use welding wire! It is a very poor material choice. It rusts (and as with aluminum) you'll have connection problems in no time.

Beverage Supports

Some would have us believe we need non-metallic supports for our Beverages, but there is not the slightest technical justification for such suggestions.
The only requirement for the support is it must hold the antenna up, and it can not connect the antenna to ground. A metal pole with a small PVC stub for an insulator is every bit as good as a full non-metallic pole. Trees make good supports, especially if you use nail-type electric-fence insulators for use with wooden posts.
I've never seen a problem allowing a wire to contact a branch, although I do trim out the branches and avoid any contact with trees.
For end supports, I use trees, pressure treated lumber, or landscaping timbers. With a lot of tension, I backstay the poles to a dead-man (generally an old brick) buried in the ground. When I set end-posts with my power auger, I line the hole with copper flashing. That becomes part or all of the feed point (and termination) ground connection.
I never anchor or wrap the Beverage wire around insulators, except at the ends. I always allow the wire to "float" through the insulators. When the wire floats, you can tension the entire antenna from either end. If anything breaks the wire, you can see it at any point! A "floating" wire is much easier to repair if it is damaged, because you only need release tension on one end to splice the wire. Re-tension that same end, and everything is restored. It takes no more tension to support a 1000-foot Beverage with supports every 100-feet than it does to support a 100-foot wire between two rigid supports, but it is a much more difficult to break the longer wire. A longer "floating" wire will often take-up enough slack to remain up after deflecting a large tree branch, where a shorter rigidly-anchored span will almost certainly break either the insulators or wire.

Beverage Insulators

If you expect a long-lasting antenna and have a long antenna, be careful when choosing insulators! Some types of electric fence insulators will not last long. The unreliable types of post insulators have two square folds to hold the wire, a square shaped base, and nail through a small molded plastic angle. The weak points of this insulator are the square retaining tabs, and the molded nail tube at the insulator base. When this type of insulator is mounted horizontally, the wire's weight will stress both the molded nail tube and a single tab. I typically find about 10% of the insulators fail within a few months. After three years, the few dozen installed here have virtually all failed.
Avoid these types!
Round yellow or back plastic insulators with the nail going through the center, like the examples below, are much more reliable post insulators
Ceramic post insulators may look great, but they do not allow floating the wire across the insulator. Even if you do manage to find a ceramic insulator that allows floating the wire, the ceramic will quickly wear away at the constantly moving wire. Avoid ceramic insulators, unless you are prepared to "buffer" the wire through a UV resistant soft plastic bushing!
Good end-insulators are becoming difficult to find. I always use compression types, but the material has to be either ceramic or very thick plastic. Some very thin plastic compression insulators will actually cold-flow and allow the wire to pass through the insulation. This is particularly true with thin steel wires that are tensioned over 25 pounds. Heavy-walled egg insulators are much more reliable, and not subject to wire migration through the thin insulation.
My favorite insulators are large these rather thick Fi-Shock yellow plastic insulators. They are slippery enough to allow the dead-end wire or rope to loop over the insulator, and create a 2:1 mechanical advantage when tensioning.

Height

I've found very little performance difference with height, unless the Beverage is more than .05WL high. As the height exceeds .05wl, performance seems to be reduced. Small rolling hills or ravines also seem to make any difference. Follow the contour of gradual slopes, and go straight across ditches or narrow ravines without following the contour.

Sloping Ends

There really isn't a logical reason to slope the ends of a Beverage. After all, six-feet of vertical drop is six feet, no matter if the drop is over 50 feet or straight vertical.
Consider, for example, the K9AY or Pennant antennas. Both have sloped wires, yet virtually all of the response is from the vertical slope of the wire in the antennas. As a matter of fact, the actual shape makes very little difference in the way each antenna works. Why would anyone, knowing how a Pennant or K9AY works, think that a Beverage somehow magically breaks tradition and stops responding to vertical signals in the wires when we slope them a bit? What difference would it make in noise anyway, since the entire antenna responds to vertically polarized signals?
There isn't any possible way, including use of shielding or additional conductors, to prevent the end-wires from having the very small effect they have. Save yourself time and worry, and avoid a needless hazard. Just drop the end-wires vertically right down to earth.
will continue...
 

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