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Old 15-10-2009, 07:32   #1
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SSB and Split Backstay

I have read about NOT using an insulator at the bottom of your backstay when using it as a random-wire antenna for your SSB. The arguments make sense to me and have convinced me that I really only need an insulator at the top.

Now, what if I have a split backstay? Do I still only need an insulator at the top? Or am I going to have problems with the split creating some crazy pattern in the antenna's radiation?
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Old 15-10-2009, 07:38   #2
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Depends. What kind of split backstay do you have? Are there really TWO backstays which run all the way to the truck of the mast (sometimes called a "split backstay")??

Or, do you have a single backstay going most of the way up, and a split nearer the bottom end (also called a "split backstay")??

Are the backstays grounded?

How big is your boat (how tall is your mast?)??

Bill
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Old 15-10-2009, 07:53   #3
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Actually don't have the boat yet. Still looking, but...

Two of the boats I am considering have the Y type of split backstay. Both are in the 34-36 foot range. Backstay(s) are not grounded--just chainplates into the fiberglass at the stern. The singular portion of the backstay, that goes from the mast to the split, is on the short side to make an effective antenna.
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Old 15-10-2009, 08:07   #4
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Usual way of doing it with a Y-type split is to insulate ONE of the sides of the Y, just below the split. This is the portion to be left out of the antenna system.

Then, jumper the other one to the longer portion if necessary (many times it's not, since they are electrically connected anyway with the Y-fitting), and put ONE insulator up a couple of feet from the top of the mast.

Feed the split backstay from belowdecks, and you have it. You can put some nylon or PVC covering over the lower split if you want.

Also, of course, you need a good RF ground. Simplest is a copper strap to the nearest bronze thru-hull.

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Old 15-10-2009, 11:47   #5
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Yeah, I understand that is the "usual" way of doing it. What I'm wondering is what affect it will have on the antenna effectiveness if I avoid the hassle and expense of isolating one leg of the Y and only put an insulator at the top.

I guess what I need to do is to finally figure out how to use the antenna modeling software that I got when I bought the ARRL Antenna book, so that I can see what sort of patterns I would get with only one insulator, and then with two.
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Old 15-10-2009, 13:42   #6
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What does an insulator cost? We have replace a couple backstays with Dynex Dux and eliminate the wire and insulator. Dux is it's insulator, you run a copper wire up the outside and be done with it.
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Old 15-10-2009, 15:17   #7
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You don't need any insulators. Take one split of your backstay and connect it to the antenna tuner output. The other split and the antenna tuner ground are connected to RF ground. The acute angle of backstay at the masthead does a fair job of decoupling the RF on the backstay from the mast. Almost as good as an insulator located a couple feet down the backstay. You will need to insure that the split backstay junction is clean with good metal to metal contact. You now are the proud owner of an off-center feed grounded sloper antenna.

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