Skin Effect Calculator

[aa5wg]

Tom:
Excellent data.
Thank you for this work.
Chuck

[k4kyv]

As far as r.f. resistances –
I looked through my trusty old “Radio Engineers’ Handbook” by Terman for wire a.c. resistances.  On page 35 of my edition is the wanted information.  This is Section 2 of the book called Circuit Elements, part 4. Resistance at Radio Frequencies – Skin Effect.  There is equation (6) for a.c. resistance and then Figure 4 follows, which is a graph for r.f. resistance versus frequency based on equation (6).  If I pick on the graph a solid copper wire of the same area as the 0.003” cladding on the surface of a #8 AWG, which is about equal to a #18, I came up with a resistance of 332 milliOhms for 10 feet at 1.8 MHz., if I did all conversion math correctly.  This is 5.2 times the dc resistance of # 18 solid copper wire.  So it appears that the wire you have is o.k. at 160 meters.  

Tom,

Thanks for all the research. I probably have most of the reference material, but that would have taken me hours.

I haven't studied the graphs yet and that will likely clarify my question, but at first glance it would appear to me that copper clad, or thin hollow copper tubing would have less rf resistance than would solid copper wire of the same (copper) cross-sectional area, since (in the cited example), due to the skin effect, a substantial portion of the copper in #18 solid would carry little or no rf current, whereas nearly all the copper in the .003" #8 cladding, which lies almost entirely within the first skin depth, would carry rf current.

For the radiating part of the antenna, or for long stretches of OWL, I would want to use hard-drawn solid copper to avoid stretching.  I did check some on-line vendors, and found that #8 is THE one size that is hard to find.  #4, #6, #10, #12 and #14 are readily available, but not #8. I did find an outfit in CA that lists #8 bare solid hard-drawn copper, but they didn't list prices. But my test results showed that the #8 copper clad I have on hand is perfectly satisfactory, so I didn't bother to enquire further.  I might have decided otherwise if I were using the line to run a high SWR tuned feeder, or as a short wire antenna with low radiation resistance, but running flat circa 450-ohm line, the loss is negligible, much less than measured with an equivalent length of fresh RG-213 or RG-214. At a kilowatt of carrier, the rf current in 450-ohm line is approximately 1.5 amps.

But then, many of the commercial wire antenna arrays from the 1920s on, used phosphor bronze wire for antennas, and phosphor bronze despite its excellent mechanical properties has a relatively small fraction of the conductivity of copper.  Even #18 solid copper would probably have less rf resistance.

Considering the rf current and voltage at a given power level (at low SWR), I would say that 450 ohms is far more optimum for a transmission line Zo, than is 50 ohms.

What I don't understand is why the vendors have such an aversion to #8 gauge.

[Rob K2CU]

The real question is whether it is Oxygen free copperweld or not.

Consider this:

#8 AWG copper is listed as .000739 Ohms per foot.

#8 AWG copperweld at 30% conductivity would be .0024633 Ohms per foot.

#12 AWG copper is listed as .00187 Ohms per foot and
#14 AWG copper is listed as .00297 Ohms per foot.

So therefore, your #* copperweld, forgetting any skin effect improvement, would be like #13 AWG if it were available, and a 100 FT length would be .24633 Ohms for a single wire and as a balanced feeder line would introduce .49266 Ohms resistance. if you have created 400 or 450 Ohm balanced line, then that would be a 0.1% effect on the impedance. Consider that solder joints are .02 to .05 ohms each.

So if you have lots of #8 AWG copperweld available, use the stuff!

I have used copperweld in the past with good success. The major objections were due to the stiffness when in came to bending it around an egg insulator. You need to use padded pliers to bend the stuff. Any nick in the copper skin will allow the elements to get at the steel and greatly shorten the service life due to internal rust out.

[KM1H]

* Maybe Carl KM1H can run a 5’ single-turn loop of wire on his HP bridge and compare Copperweld and solid wire at 1.8 MHz. also, if that bridge can resolve very low resistances.

Not with accuracy I would trust Tom, it would require a substantial amount of Copperweld and solid copper to make an A:B comparison of relative resistance difference rather than rely on an uncalibrated absolute.

A better approach IMO is to measure the power loss in a reel of RG-6 at various frequencies from 1.8 to say 14MHz and plot where it deviates from a linear path. From what Ive read of other testing RG-6 has about a 1-3% additional loss on 160 and none on 80. Except for the roughly 100' run on an 80M sloper all other runs here are short ones in the house or up to 200' or so from Beverages to the relay boxes and with Beverages a little loss is a good thing.

Don, I have two issue here..First, the CATV line is made of a copper plated aluminum conductor, not a steel core

Bill, that is correct for the hardline but that was not done for the frequency ranges mentioned by Don. The original hardline was solid copper center conductor BUT the connectors are aluminum and cold temperature creep caused center conductors to pull out of pole mounted hardware due to the different coefficients of expansion/contraction.

Drop cable such as RG-59 and RG-6 is almost always copper clad steel, all copper RG-6 is available now.
CATV/MATV RG-11 Type can be either #14 solid copperclad, or all copper solid or stranded. It pays to read the specs before ordering and its intended application.

Carl

[w3jn]

You might try measuring the Q of a loop of copperweld vs a loop of solid copper at the appropriate frequency.

[Tom WA3KLR]

I would think that #8 copperweld is getting unwieldy and somewhat heavy. 

If ordering new wire, my impression is to stick with the 40 % conductivity and go with #14.

[k4kyv]

The stuff is strong, though.  The bloke I got my roll from, used it for tower guy wire.  He had three towers, each about 100' tall, made of Rohn 20G (that light duty stuff sold for holding up fringe-area TV receiving antennas), guyed every 20 feet or so.  He said the towers had been up for over 15 years and had survived some pretty tremendous wind storms that we periodically have in this area.  He had a bunch of VHF antennas on each of the towers, and some HF wire antennas strung between them.

I also use it for my beverage antenna.  Using a ratchet puller, I can pull almost all the sag out of it with supports only every couple of hundred feet.  It is easy to work with, using a ratchet puller to stretch the wire, and turnbuckles to adjust the final tension.  The OWL was easy to make, using similar techniques. You have to be careful when pulling tension, since an out-of-control piece can come flying back at you in the form of a deadly missile.