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Author Topic: HF antenna LOADING COILS  (Read 3683 times)
KF2YR
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Posts: 10




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« on: November 16, 2007, 01:24:21 AM »

I am trying to recreate my "lost" W9INN loaded dipole antenna. I am going to wind my loading coils on 1 1/2" PVC pipe, using 14g. enameled wire. I hope to run at least 1KW into the antenna.
From what I have been able to figure out, I need to have an inductance of 10.512uH, on my 40 meter antenna leg. Having NEVER attemped winding coils, I not sure on the wire shorting out OR overheating.
 
My question is should I space the windings out (1-14g.wire width spaceing) OR would close winding be better???
Would the insulation from the enammeled wire be enough to allow the wire wraps to touch each other>>>OR would the 1/16" spacing of 14gauge wire be better???

THANKS for taking the time to read this. All resonable thoughts/advice are wecome!
Jim KF2YR  
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K7AAT
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Posts: 413




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« Reply #1 on: November 16, 2007, 05:46:36 PM »


  If you really want to do a classy job of winding your coils, e.g. something like B&W Miniductor coils,   then go to:  http://www.qsl.net/n1lo/antenna.htm   and scroll down to the bottom to the "80-10M mobile vertical" and click on that.  In the instructions that will come up will be excellent detail on how to build what is essentially miniductor coils, and also includes where to get the materials.  I have built a few antenna coils with this design and have never regretted going this route.

  Good luck.,

   Ed    K7AAT
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AA4PB
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Posts: 12832




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« Reply #2 on: November 16, 2007, 07:54:33 PM »

For 1KW you should probably leave a little spacing between the turns. If the coil is open its going to get wet in the weather.
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WB6BYU
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Posts: 13231




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« Reply #3 on: November 17, 2007, 08:18:40 PM »

I'd leave a gap between turns if you are going to run full power.  You'd
have to calculate the actual voltage across the coil on each band (which
EZNEC can model for you) then from that figure the voltage between
adjacent turns.  That is the voltage that the insulation has to withstand.
Depending on how you wind the coil,  you may be able to get by with
close-spaced turns, but that also increases the self-capacitance of the
coil.  Spaced windings generally give a higher Q coil.

ON4AA's excellent coil calculator is available at:
http://hamwaves.com/antennas/inductance.html

If you are going to wind the coil on a piece of PVC pipe, secure one end
temporarily then put the whole thing in the freezer for an hour or so.
The pipe shrinks more than the copper wire, so you can then work some
of the slack out of the wire and tighten it up.  The wire will warm from
your hands, so give it a couple of tries.  When you are done and the
coil is back up to room temperature, the wire will compress the pipe
slightly and the turns will be very hard to move.
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