Use Galvanized Electric Fence Wire or Copper for Loop?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by NW2K, Nov 17, 2010.

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  1. NW2K

    NW2K Ham Member QRZ Page

    I just raised a 550 ft loop of 17 ga "galvanized" electric fence wire (GEFW). Loaded up fine; SWR was amazingly flat, which drew concern....Made a few contacts.

    Put up antenna first, think, second.

    I searched the forum and found inconclusive debate regarding the use of GEFW for HF antennas.

    The DC resistance of the 550' loop measured 19 ohms. Assuming that the zinc layer is very thin (a fraction of skin depth), GEFW looks like "iron" or "steel" and not zinc.

    At HF, given internet data for iron, I estimate the following for 550' of 17ga (diameter = 0.055") GEFW:

    Freq (MHz) AC Resistance (ohms) Assumed Wire Resistance (ohms)

    2 550 275
    5 880 440
    15 1540 770
    30 2200 1100
    50 2750 1375

    Assuming the loop radiation resistance is 100 ohms at the fundamental and harmonics (I have no idea what it is exactly):

    Antenna_Efficiency = Radiation_Resistance/(Radiation_Resistance + Assumed_Wire_Resistance)

    Freq (MHz) Efficiency (%)

    2 27
    5 19
    15 11
    30 8
    50 7

    Yes, there are a lot of assumptions. Most importantly, if 17ga GEFW looks like iron to HF, then antenna efficiency will suffer.

    For comparison, AWG 14 solid copper (I have some on hand otherwise I would have looked at AWG 16 for a closer comparison) gives:

    Freq (MHz) Efficiency (%)

    2 88
    5 83
    15 74
    30 66
    50 60

    Penalty of using the assumed 17ga GEFW vs. AWG 14 solid copper:

    Freq (MHz) Approx. Loss Penalty (dB)

    2 -5
    5 -6
    15 -8
    30 -9
    50 -9

    So, it seems that for a 160m full wave loop, dollars per dB says to use copper. But, anything works!

    PS Sorry, I could not get tabs to work properly in the tables...
  2. VK1OD

    VK1OD Ham Member QRZ Page

    So much depends on the thickness of the zinc coating.

    Modern fence wires in this country are coated with ZincAluminium (Zal) and then a polymer coating. The blue polymer coating protects the Zal, and so they have even less thickness.

    Even heavy galvanised wires are unlikely to have good performance at lower HF. (At higher frequencies, skin depth is smaller, and more of the current flows in the zinc layer.)

    I recently wrote some notes at Loss in antenna conductor materials which you may find interesting.

    If you apply the thinking to some of the commercially advertised antenna wires, you would wonder why people buy them... but as you intimate, any thing 'works' whatever 'works' means.

    BTW, the issue also exists with some very popular feed line products.

    Last edited: Nov 17, 2010
  3. NW2K

    NW2K Ham Member QRZ Page

    Owen, thank you very much for the information and your help.

    The following table is a correction to the efficiency for the copper loop:

    Freq (MHz) Efficiency (%)

    2 93
    5 91
    15 85
    30 79

    and a correction to the penalty of using the assumed 17ga GEFW vs. AWG 14 solid copper:

    Freq (MHz) Approx. Loss Penalty (dB)

    2 -5
    5 -7
    15 -9
    30 -10

    I still do not know anything about the makeup of the bare GEFW itself. Not sure what I have in the air. No problem, though, since it is coming down quite soon.

    Through this, I think I learned some about copper clad steel (CCS) coax. I am currently using about 140 feet of CCS RG-6U to feed the loop. Its DC resistance (18 AWG center conductor) is about 5 ohms. This is consistent with 21% CCS, where the nominal thickness of copper is 6.5%. This gives a copper thickness of 34 microns (0.0013") over low carbon steel.

    Freq (MHz) Skin Depth (Cu)
    1 0.0026"
    3.5 0.0014"
    7 0.0010"
    14 0.0007"

    where skin depth is defined at 1/e.

    So, for 21% CCS, 0.0013" of copper cladding might be acceptable to some at 14 Mhz and higher (e.g. >2 skin depths). But it is a killer at lower frequencies.

    30% CCS (18 AWG) has a cladding layer of copper of 0.0024" over low carbon steel.

    40% CCS (18 AWG) has a cladding layer of copper of 0.0036" over low carbon steel.

    Some CCS coax might be cheap, but it has real costs on HF. My GEFW loop fed with 21% CCS coax is a real heater.
  4. KD0CAC

    KD0CAC Ham Member QRZ Page

    Not to be argumentative , but the cheapest wire you can put up , cost being the largest affect ?
    Wouldn't the difference between wire avalable be very minor .
    But at the other end , with like many hobbies , escalation of technology to the extreme , some have the cash flow to go the extra little .
    Like in shooting competition , take one of the top ten shooters give them a quality gun , that has been accurized , as compared to a total custom job .
    There are two differences , the top shooter is going to be in the money but may lose by a hundredth of a second with the stock gun .
    The subject is interesting , but just a guesstimate , the small percentage of gain does little , but the knowledge has value .
    The point being that in shooting competition , it was hard to get new shooters involved because the 1st thing they looked at was the cost of buying what everyone else had .
    Either a $700 stock gun with $200 worth of accurizing , or a $4,500 custom job , for 2 tenths of a second ?
    I like to buy the high end stuff , but in order to play , I will just through some wire in the trees .[​IMG]
  5. W9GB

    W9GB Ham Member QRZ Page

    Galvinized Electric Fence Wire (GEFW) will work as an antenna conductor (wire).
    I used GEFW for a short period of time in 1970s .. GEFW was actually galvinized steel wire in 1970s.

    I also worked with solid CopperWeld antenna wire -- recommended by a few Old Timers to me (as a Novice) in 1970s.
    I don't recommend either antenna wire for a HF antenna builder today, WHY?

    1. STRANDED wire is much easier to work with than SOLID wire for Antennas.

    2. GEFW can exhibit same issues as CopperWeld (especially solid wire) -- coil memory -- which can make some antennas difficult to construct.

    3. GEFW and CopperWeld can rust, IF the coating (Zinc or Copper) is removed by abrasion, rubbing, or mis-handling.
    These corrosion/rust points then become the weak points (breakage, lower conductivity) for the wire antenna.

    Once I switched to STRANDED (at least 7 wires) 14 AWG, many of my fabrication issues disappeared --
    only wish I had been advised correctly when I was a Novice!!

    BTW, COST was not an issue at that time -- since both wire types were readily available to me as surplus!
    "End of Rolls" (1,000 foot spools) with lengths less than 100 feet were very common at commercial construciton sites in 1970s (Thrown in dumpsters).
    These were perfect for 40 meter dipole construction.

    Last edited: Jan 4, 2011
  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    The HyGain HyTower is basically a galvanized structure for 40 through 10 meters. The 80 meter section is copper and aluminum. That particular antenna works very well. AM broadcast towers are galvanized steel and they work well.

    Over the years I have used galvanized fence wire, both 17 gauge and 19 gauge for wire antennas and those worked well. Replacing the galvanized wire with copper wire did not show any measurable improvement in performance. My elevated radial system for both my HyTower and the full sized 40 meter vertical that I phase with the HyTower are made from galvanized fence wire.

    In theory every antenna should be silver plated. However, the cost of doing this is beyond the price range of virtually everyone. Therefore, the vast majority of antennas are made from copper, aluminum, and galvanized steel. Are those antennas perfect? No! But, in the "real world" antennas made using those materials work very well.

    Glen, K9STH
  7. VK1OD

    VK1OD Ham Member QRZ Page

    HI Dean,

    As you note, when you explore the effects, it unsettles some who are duty bound to inform you that you are naval gazing. I expect that someone will inform us that less than 6dB doesn't make a difference.

    Regarding the CCS RG6, Belden have captured the effect of the CCS conductor in some of their RG6 cables in their published loss figures. When I create the models for lines in TLLC , I check departure from the model at the low frequency end. For several lines I delete some lower frequency points because the lines are not predictable at those frequencies using the k1f^0.5+k2*f loss model. The ONLY lines where this has happened have been copper clad steel or silver clad steel.

    So, if you lookup Belden 1189A loss at 5MHz, they quote 0.67dB/100'. TLLC gives just two thirds of that, 0.43dB/100 based on a pure copper model using datapoints from 55MHz to 1000MHz. The departure from copper model grows as frequency is decreased.

    I recall W7EL reporting loss of small size teflon coax with silver plated copper plated stainless steel centre conductor in his portable HF station. I cannot find a reference for you, but as I recall, whilst this coax had good properties at UHF and above, it had far to little silver coating to deliver good performance at HF and its loss was much worse IIRC than at UHF. In this case, the departure from copper like performance was so severe that he went looking for reasons why the station performed so badly.

    G8JNJ related the following recently on 'that other ham' site:
    He told me by email that the wire was in fact 19 strand #26 copper clad steel sold by Wireman for stealth antennas. The on air performance was much worse than the 0.7mm (#21) tinned copper wire prototype. Note that tinning copper wire increases its RF resistance, so although this was nearly twice the diameter, tin has a conductivity of about 15% of copper.

    I would not try to compare a galvanised tower structure to a thin galvanised wire, there is no comparison, one is much larger in diameter and should have much thicker zinc layer, probably thick enough to approach zinc like conductivity of the large conducting structure vs a thin wire with probably less than skin depth of zinc and likely to be poorer than a small diameter zinc conductor. Not everyone will see that difference.

    If you ignore the effects of conductivity, you will sometimes be caught out.

    On the other hand, lossy conductors tend to improve bandwidth and reduce VSWR... the two highest priority parameters in some peoples minds.

  8. KC2UGV

    KC2UGV Ham Member QRZ Page

    Seriously, I thought all this time there was an antenna being supported by the tower, not that the tower itself was the antenna... :eek: Now, I'm going into the corner.
  9. W8JI

    W8JI Ham Member QRZ Page

    As Owen says, a tower has very large surface area so conductivity matter much less than with a thin wire.

    Also, the length of the conductor matters. On ten meters an antenna is not very long, so resistance is low even with fairly poor conductors. On 160 meters, especially with a large loop with 500 feet of conductor length, a little resistance per foot adds up!!!

    The conductor in my 160 dipole is much more important than the conductor in my ten meter dipole because one antenna is 16 times longer. Make it a full wave, and resistance per foot is even more meaningful.

    I've had terrible results with electric fence galvanized wire on 160 and 80 meters.

    73 Tom
  10. KR2D

    KR2D Ham Member QRZ Page

    How does aluminum electric fence wire compare to copper? Sellers claim that it is " four times more conductive than galvanized steel". It's fairly cheap, too: $38 USD for 1/4 mile (402 meters) of 14 AWG at TSC.

    Mechanically, would would 14 AWG aluminum work for a 160m dipole or fullwave loop?
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