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Author Topic: Why is stranded wire preferred?  (Read 816 times)
AG4DG
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« on: January 03, 2001, 10:58:01 PM »

Why is stranded wire preferred over solid wire for wire antennas?  In my opinion, solid wire is easier to work with, as you don't have a myriad of strands to mess around with.
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ZL4CG
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« Reply #1 on: January 04, 2001, 05:01:13 AM »

It has to do with skin effect.RF travels on the surface
the more strands the more surfaces.
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N2MG
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« Reply #2 on: January 04, 2001, 08:35:44 AM »

I wouldn't make such a general statement that stranded wire is preferred.

Stranded wire tends to be more flexible - a good characteristic for antennas.  Also, if a strand gets nicked and subsequently breaks, one only loses the single strand, not the entire wire.

However, after being out in the weather, most wires will eventually get wet or otherwise oxidize.  When stranded wire oxidizes, it becomes quite difficult to correctly repair (and you WILL need to repair it from time to time), because the individual strands must be cleaned to allow a good connection (soldered or not).  Because of this, some hams prefer making antennas out of solid wire - especially antennas that tend to break more often (like low Beverages and radials).

Maybe I'm wrong, but I don't think that skin effect has anything to do with any preference for using stranded wire.  Skin effect exists, but I believe on the overall surface, not the surfaces of the individual strands.

73 Mike N2MG
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WA2AEH
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Posts: 21




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« Reply #3 on: January 04, 2001, 08:51:45 AM »

Stranded wire is much easier to work with period.  I use insulated stranded wire #12 gauge.  The heavier the wire the broader the bandwidth of the antenna.  Using insulated stranded wire is the best way to go both for mechanical strength and durability.

Bill
WA2AEH
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WB6BYU
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Posts: 13485




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« Reply #4 on: January 04, 2001, 12:27:08 PM »

Stranded wire is more flexible, and less prone to stress fracture
from repeated flexing.  This is important if your antenna blows in
the wind.  However, if you use large enough wire (or steel-cored
"copperweld" wire) this isn't a problem.

I like insulated, stranded wire because it winds up easily and I
can tie knots in it just like string.  But it really doesn't matter,
especially for indoor antennas.  Use whatever you have handy -
even aluminum foil from the kitchen or galvanized rain gutters or
steel tape measure blades (great for flexible yagis) or burglar alarm
tape or heating ducts or thin magnet wire from an old speaker or
transformer you have unwound, or wire sold for clotheslines or
wiring the house or electric fences or speaker cable or barbed wire.
(Did I miss anything???)
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WB2WIK
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Posts: 20636




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« Reply #5 on: January 04, 2001, 07:25:21 PM »

Previous comments are good.  I always prefer and recommend not just stranded wire, but wire with LOTS of strands, and preferably OFHC copper (oxygen-free, high-conductivity) which really lasts a very long time outdoors, insulated or not, and if a splice becomes necessary, the individual strands do not require cleaning: Just dip the end of the stranded wire in liquid flux, wait a few seconds, twist conductors and flow solder.  It's a cinch.  The 168-strand "superflex" (sold under various names) pure copper #14 gauge wire is a great compromise between strength, weight, performance and cost.  Insulated wire is highly recommended for outdoor use where the wire is likely to suffer abrasion (rubbing against tree branches), but be careful about the kind of insulation chosen -- many wire insulation materials used are not very flexible, and weather even worse than the wire!
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N6QTH
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Posts: 42




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« Reply #6 on: January 04, 2001, 11:49:08 PM »

I do prefer stranded wire over solid copper or copperweld, especially when I'm experimenting and need to make various adjustments over time.  Stranded wire behaves better mechanically.  It coils and uncoils smoothly and lays fairly flat, unlike solid wire (especially copperweld) which often behaves more like one of those slinky toys of the 50's.  Because it behaves, stranded wire is easier to measure while lying flat on the ground or other surface.  I use AWG10 for most of my wire antennas and support it with parallel 80 pound test nylon line tied to the wire at two or three foot intervals with nylon ties.
While skin effect is clearly a reality,  I don't believe you will find much electrical advantage (at least not measureable) in using stranded wire over solid.  But it might be worth doing some experiments.  If your results prove sufficiently interesting there are plenty of publications waiting to accept your technical article on the results.
In my experience, it isn't worth the time it takes to do the math to factor in skin effect at lower frequencies.  There are a couple of suppliers on the Internet that will ship you the stranded wire at a very reasonable rate.  Wire is where it's at.  Good luck.
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K0UM
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« Reply #7 on: June 13, 2003, 01:09:18 AM »

Surface area is a concern, and more so at higher frequencies.  The wire will have a higher impedance at HF frequencies than at DC due to skin effect.  Some engineers specify multiple strands of small wire or flat straps to increase the surface area and decrease HF impedance.  However, simply using stranded wire--where all of the strands are bare and shorted together--will act just like one solid conductor.  You would need to use "Litz" wire--which is many strands of wire with each strand insulated from eachother.  Litz wire usually has a bundle of varnished strands (looks like a transformer winding).  This is quite common for high frequency switch-mode power supplies where the engineer doesn't want to go to strap windings on transformers.  This being said, I've never heard of someone using Litz wire on an antenna (maybe a small loop, but not any outdoor, flying antenna).  So, best bet is to use copperweld, either stranded or solid, depending on your dexterity with solid.
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