Topband: A few beverage planning questions

[Jon Zaimes AA1K]

Hi Jerry,

Good time to get on the band -- things are really getting hot!

At 10:07 AM 2/5/05, you wrote:
>I'm spending the winter devoloping a plan for my first attempt at getting on topband in 2005. I've been reading ON4UN's book, plus K1ZM's book with the photos of some of you. This topband reflector has also been of help... thanks. To start with, I want to try shunt feeding my 45 foot tower, plus one or two beverages for receiving. I have a few beverage construction questions that I hope are not too basic (numbered for convenience in answering):
>
>(1) I was planning to run 50 ohm coax with the rest of my feedlines, from the shack out 50 feet thru underground PVC pipe.... to an Ameritron remote switching unit in a box at my tower base. As these are receive only, can I run RG59U from the box to each beverage without "mismatch" degradation? Or should I use RG59U the entire distance?
Either impedance should work fine. If you are a purist, you can use matching transformers but the loss of the transformer might just equal (or exceed) the slight mismatch of the coax. I have used both 75 ohm and 50 ohm, either works fine.

>(2)Are the distances from my tower to the feed point for each beverage important? Is there a minimum distance I should observe?

The tower will tend to couple noise -- precipitation static, line noise, etc -- into the Beverage. But if you don't have room to separate them, you do what you can. Ideal separation might be a half-wavelength -- but even greater distance might have some coupling. I have a phased pair of 935-foot Beverages toward JA that run within 10 feet of one tower and 20 feet of another (my TX vertical for 160) and this pair tends to be noisier than most of my other Beverages. However, it is still my best receiving antenna for JA. A single 500-foot wire that is a couple of hundred feet from the towers is quieter but generally the phased pair still hears better even with the additiional noise.


>(3) Will wire antennas minimum 40 feet above a beverage significantly degrade performance of either?

I have run Beverages under delta loops (only a few feet above the Beverage)  and other wire antennas with no obvious degradaton. Again, wider separation would be better because there is probably some coupling. But I have found the first priority with Beverage placement is to put the antenna in the desired direction and as long as possible (up to a wavelength or two) -- then worry about keeping it separated from other antennas. So if you don't have room to move the antenna away from the tower AND keep it in the desired direction, let it be near the tower. An exception to his was one set of phased Beverages that I tried running under the power line feeding our house. There was just too much noise coupling -- so I finally shortened the wires from 760 feet to 465 feet to keep them at least 50 feet from the power line. Now this is a very quiet antenna.


>(4) Is there a minimum distance that I should separate the beverage feedpoints?

I have run as many as three to a single feedpoint, with relays there for switching, and grounded the unused wires. I have piggybacked the control voltage on the feedline. They worked, but more recently I have used separate feedlines on all my Beverages and try to keep them separated at least the height of the Beverage (10 feet is typical) though usually twice the height.
>(5) How important is it for a beverage to run in a straight line?

I have an 880-foot, 10-foot high Beverage to the southeast that is in a straight line. I recently added a 1000-foot, 4-foot high Beverage in the same direction but it follows the property line -- which the surveyors aptly described as "following 18 courses along a meandering ditch." In other words, this wire zig-zags along its length. But the "average" works out the same as the straight-line Beverage. I have run numerous A/B tests on these two and performance seems to be identical; the lower one might be just a bit quieter.


>(6) I've been reading that beverages perform differently at different heights above the earth, but does it matter very much if the height above earth varies along the length of the beverage, say, between 6 and 12 feet above earth?

Again, think of the "average" height of the wire. ON4UN wrote about doing this with a single support point at the center of the wire, with the ends sloping to ground level. I keep all of mine at a constant height above ground instead, but occassionally a tree will fall on the wire bring it down to ground level. They still work fine.


>(7) I think I understand about tapering down at the ends to avoid noise from vertical components, but what would be a good minimum from the ends to start the taper?

I have tried them both ways -- with tapered ends and straight-down ends -- and can't tell any difference. W8JI has found the same thing. It's nice to keep them above head (and deer) level so I don't walk into them while walking through the woods (and I have a lot of wires in the woods!).


>(8) Is insulated wire better or worse than bare?

W8JI did some tests and found no difference. I decided to test this with the new SE Beverage I mentioned above -- the 1000-footer is bare aluminum electric fence wire, no. 18 I think. The 880-footer is no. 18 insulated wire. And they work about the same. Most of mine use insulated wire  -- no. 12 THHN house wiring type -- simply because I can get it cheap from local scrap yards and it is pretty durable when trees fall on it.

>(9) If I use insulated wire and trees as supports, can I just staple the wire to the trees? Or should I use an insulator? If an insulator, is the standoff distance from the tree significant to performance?

Trees tend to make great insulators. If I'm in a hurry I'll just toss the wire over tree limbs. Where they aren't in the right spot I'll use electric fence plastic insulators, driven into the tree with a nail.  The downside of these is after a couple of years the tree will grow around the insulator and wire. So a better way for longterm use might be to use a short 2x4 to keep the wire off the tree.

>(10) Aside from durability concerns, will I get better performance from #14 vs #22 wire? Or stranded vs solid wire?

No difference -- wire is wire. The size will make a miniscule difference in the impedance of the antenna.

>(11) I hope to eventually put in several beverages, but will start with 1 or 2.  I'm in eastern PA on top of an east/west ridge, so beverages will slope gently downhill towards the north. I'm thinking first, a 500' NE/SW for EU. Second one could be 500' NW/SE. After that I don't know, but are these two a good way to start out?
Going back to my first priority of Beverage placement -- put the wire in the desired direction, and add to that to  use a terminated Beverage to make it  unidirectional. If you want to receive both NE/SW from the same wire, run a feedline to each end and switch it using control voltages piggybacked on the feedline. Or use a 2-wire, reversible Beverage. Northeast is certainly my first priority of directions -- lots of Europeans, Mideast and central Asians in that direction. NW is good too -- JAs coming through many days right now.

73/Jon AA1K
Felton, Delaware
www.aa1k.us

>Any ideas or suggestions will be appreciated.
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>73, Jerry K3BZ
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