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Looking for Stealthy Long Wire

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by NN5RR, Mar 17, 2011.

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  1. W0BTU

    W0BTU Ham Member QRZ Page

    I respectfully but strongly disagree. It's not only about the resistivity of the material, it's about the permeability. If you only read http://forums.qrz.com/showthread.php?272474-Use-Galvanized-Electric-Fence-Wire-or-Copper-for-Loop, you would understand. W8JI says it short and sweet there when he stated "I've had terrible results with electric fence galvanized wire on 160 and 80 meters".

    To quote Dr. Jeffries in the above-referenced PDF file, "we repeat the admonition to avoid conducting materials with large relative permeability, which in practice means avoiding any magnetic material or material attracted by a magnet. In such materials the loss is large".

    Some hams like QRP or QRPp. An alternate way to do that is to use magnetic wire for your transmitting antenna. :)
     
  2. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    And the point everyone is missing is two fold.

    First Tom had a bad experience with electric fence wire and attributed it to the wire.

    Second, on a thin random wire that most likely has a high feed point impedance and looks capacitive at the frequency in question there is not much physical area for dissapation of power so before one more wannabe expert comes in here and quotes some other expert I challenge you to actually build identical antennas from the two materials as previously discussed. Use the same mounting structure at the same hight and the same ground system and tuner. Then do the field strength measurements using Z Tech or Tyco measuring equipment and post the results.

    Until then, this is amateur radio not commercial radio and what I suggested to WI0N will work just fine in his situation and anyone who says it won't is simply blowing smoke.
     
  3. K8ERV

    K8ERV QRZ Member QRZ Page

    I was going to suggest electric fence wire, think that is what I find at yard sales. Very dark. Might work.

    TOM K8ERV Montrose Colo
     
  4. G0GQK

    G0GQK Ham Member QRZ Page

    Just get yourself a length of single core black plastic covered wire and stretch it out and if you still think its visible paint it with matt paint. I have a 90 ft dipole made of this at 27 ft and it gets me into the US with 30 watts
     
  5. KM1H

    KM1H Ham Member QRZ Page

    I really get a kick out of those dissing others when they obviously have very little expertise to base assumptions on. Trying to combine feed point impedance with RF resistivity/conductivity is a huge clue. And didnt one of these experts say that RF resistivity decreases with increasing frequency? Hmmmm, they must use 6 gauge in their 10W speaker system also.

    10-4 good buddies.

    BTW, galvanized fence wire works well for a Beverage receive antenna since losses arent that important plus it can often result in a more stable all weather ground system antenna.

    Carl
     
  6. VK2FXXX

    VK2FXXX Ham Member QRZ Page

    % Efficiency=[Ra/(Ra+Rloss)] X 100

    Ra=radiation resistance
    Rloss =wire resistance at rf
    eg 2mm dia copper dipole Rloss on 80m =2.27ohms
    2mm tinned copper dipole at 80m =6.57 ohms
    0.9 steel mig wire dipole R on 80 m= 397ohms
    we can assume Ra =72ohms
    Brendan
     
    Last edited: Mar 26, 2011
  7. VK1OD

    VK1OD Ham Member QRZ Page

    Bill, what are you saying here?

    The effective resistance of a conductor increases with frequency due to skin effect, which is a function of frequency, and conductor resisitivity and permeability, and it might well be a hundred times the DC resistance of the conductor.

    I have seen a couple of recent comments here that antenna conductors carry currents, but no energy is converted to heat. That is quite wrong.

    The power lost as heat might be quite small for some situations, and quite high for others. Though skin effect causes higher effective resistance at higher frequencies, the length of conductors in lower frequency antennas might result in lower efficiency.

    Owen
     
  8. VK2FXXX

    VK2FXXX Ham Member QRZ Page

    BTW I calculated the OPs original 25ft wire antenna Ra as aprox 3.2ohms at 3.6Mhz.(this is NOT the feedpoint impedance)
    Any ideas what the R of a copper conductor vs the R of a steel conductor is at 3.6Mhz , 7.1mhz ,14Mhz . for 25 ft (aprox 7.5m) of antenna conductor?
    Anyone?
    Brendan
     
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