I'm building HF kits 80m EFHW kit, and in the instructions it directs you to tie a knot in the antenna wire. I'm concerned of damage to the wire. I have found no source as of yet that indicates if damage will or will not occur. I am using their kevlar wire.
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$\begingroup$ If "damage to the wire" means reducing its mechanical strength, then yes. Any knot you tie in any kind of cord will diminish the cord's mechanical strength. By how much depends on what knot you tie, and on the physical properties of the cord. Knot tiers talk about the "strength" of different knots. When they say that a knot is "strong," they are saying that it diminishes the strength of the cord by a smaller amount than a "weak" knot would do. $\endgroup$– Solomon SlowOct 7, 2021 at 0:35
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4 Answers
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It should be fine. Stranded wire will take that kind of bending easily. If you were to tie and untie the knot many times you might eventually weaken and break some of the strands, but if it's tied once and left in position, it won't create so much stress.
If you're worried, of course, there are alternatives — you could slide a small plastic bead onto the wire and glue it into place, or just pull the wire through the hole and secure it with hot glue.
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Generally, stranded wire used for antennas is fine to knot. However, thin solid wire that is knotted or kinked can develop a weak spot that can break under tension.
You would not, for example, want to knot load bearing cable used as guy wire, even at the tips. Instead, you can use a wire thimble (selected as appropriate for wire diameter and alloy).
Googling images of wire thimbles, I found this image of a cable in a wire thimble with a crimped anchor. A guy wire might use a anchor with screws instead.
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I would refrain from knotting antenna wire meant for a long-term installation. Knots in rope weaken the rope by 20% to 60% (source). I don't know of any research on knots in antenna wire, whether kevlar-reinforced or "knot" (sorry, couldn't resist the pun), but it seems reasonable to expect that tying a knot in antenna wire weakens it. You might be able to afford some additional weakness, but on the other hand there surely are lots of alternatives to a knot, such as using a thimble and a clamp. (I'd use multiple UV-resistant zip ties as a clamp.)
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I see knots being used for desktop lamps, after the wire enters the lamp, with stranded-wire. #1.) The more sharp the bend, the more you stress the wire and prepare it for breakage. As long as it's just one time, and no repeats, no bending and unbending, you should be fine. #2.) If you want to be safer, slip a little heat-shrink on first, tie the knot in the wire making sure the heat shrink is before, inside, and after, the knot (centerd, too). Then heat-gun the heat-shrink after it's knotted. Not only will that make the curvature less sharp within the knot, but it will also hold it still so repeated flexure will be less likely to occur, thereby preventing future breakage. Personally, I would also goop it up with electrical silicone sealant, as well.
