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Author Topic: End insulators  (Read 1929 times)
TTOMAS59
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« on: May 09, 2012, 04:40:34 PM »

Articles on building wire antennas always say to use non conductive end insulators. I always just tie or loop antenna wire to fishing line, twine, or rope. Doing so has shown no variations in swr from what I expected. Am I missing something since fishing line, twine, and rope are non conductive also?
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N4JTE
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« Reply #1 on: May 09, 2012, 04:44:42 PM »

Nope ,as long as you use insulated wire, no real issues, been doing that way for years.
Bob
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KK4IKO
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Posts: 67




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« Reply #2 on: May 09, 2012, 05:06:27 PM »

If you don't use insulated wire, the cord, twine, or rope can hold rain water between the strands and become conductive.  However, the insulation, especially at the sharp bend where the cord attaches, will eventually be broken down by UV and age, allowing contact between the wet cord and wire.  Insulators (cheap insurance), will prevent even bare wire coming in contact with the rope and won't absorb moisture.  Teflon-insulated wire might hold up for the long term, but it's expensive.

73

Bruce, KK4IKO
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TTOMAS59
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« Reply #3 on: May 09, 2012, 05:13:11 PM »

Truth be told I just use fishing line. I just added twine and rope as other for-instances. I know fishing line cannot absorb water so I'm satisfied. Hopefully my post won't put the ceramic egg insulator industry out of business.

Tim
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WB4SPT
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« Reply #4 on: May 09, 2012, 05:22:34 PM »

Monofilament nylon fishing line doesn't last long in my neck of the woods (lots of sun).  1/2" PVC gray electrical conduit cut to 6" do work well and are dirt cheap.
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KD2AKG
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« Reply #5 on: May 09, 2012, 06:43:10 PM »

I use PVC conduit insulators as well. A 10' piece is about 2 or 3 bucks and makes 20 insulators. If you're around a construction site, you can often get scraps for free. Conduit also works well for the center of a dipole with a 239 connector. You just need to seal it with some silicone.
« Last Edit: May 09, 2012, 06:45:23 PM by KD2AKG » Logged
WB6BYU
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Posts: 13580




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« Reply #6 on: May 09, 2012, 07:29:26 PM »

At barefoot power levels I don't both with end insulators as long as I'm using
synthetic rope.  I just tie the rope to the wire.  This works even with bare
wire (and western Oregon isn't known for dry weather.)  But usually I'm letting
a couple feet of wire hang down off the end, so I'm not tying the rope to
the very end of the wire where the voltage is highest.

Making the end of the wire into a big loop and connecting it back to itself
also lowers the voltage on the ends.

If I do use an insulator it generally is one sold for use on electric fences.
One type is like a small plastic carabiner that I can clip around the wire - this
is handy for reconfiguring wire antennas without having to untie any knots.
Another type is an "egg" (compression) insulator with open sides - this lets
me slip it around a large wire loop, for example, and tie it off to a support
while still allowing the wire to slip through the insulator and adjust itself
for irregularly-spaced support ropes.

There are times that an insulator is a good idea, however.  Natural rope
fibers such as sisal or cotton have a lower resistance and absorb more water.
Shortened antennas will have higher voltages at the ends, whether it uses
loading coils or just something simple such as a 40m dipole fed with open wire
line on 80m.  And certainly if you are running anything more than 100W.


What is the voltage at the end of an antenna?  If an end-fed half wave has
an input impedance of 3600 ohms, at 100 watts that would be 600V RMS or
under 1000V peak.  Ordinary AC wire insulation is usually rated at 600V, so two
thicknesses should be adequate.
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G4AON
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Posts: 545




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« Reply #7 on: May 10, 2012, 01:18:52 AM »

I recently installed a 20m dipole and used plastic garden twine instead of end insulators. When we had ice after a rain shower the SWR went very high, lesson learnt, I quickly added insulators!

73 Dave
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K1CJS
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Posts: 6061




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« Reply #8 on: May 10, 2012, 03:59:30 AM »

You can do it the right way the first time, or you can do it over again.  If the antenna is one that takes some effort to get up to where you want it, use insulators--even homebrew ones.  Anything that is multi-strand can and will hold water in a rainstorm.  Insulators are cheap insurance against antenna problems, so why not do it right the first time.
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KC9TNH
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Posts: 304




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« Reply #9 on: May 10, 2012, 05:10:33 AM »

You can do it the right way the first time, or you can do it over again.  If the antenna is one that takes some effort to get up to where you want it, use insulators--even homebrew ones.  Anything that is multi-strand can and will hold water in a rainstorm.  Insulators are cheap insurance against antenna problems, so why not do it right the first time.
Really.  Good grief, one can get a pack of 10 plastic corner insulators in the fencing department at the local farm supply store for less than $3.
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73
Wes -KC9TNH
"Don't get treed by a chihuahua." - Pete
W4VR
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Posts: 1198


WWW

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« Reply #10 on: May 10, 2012, 09:15:34 AM »

some folks use weed wacker cord for the supporting ropes and don't have to use insulators.
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K0ZN
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Posts: 1563




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« Reply #11 on: May 10, 2012, 03:54:44 PM »

At lower powers, things are less critical in regard to end insulators, but as the power level goes up, "Stuff can and DOES happen"....and it will usually happen in the rain or
ice.  Dirt and dust collect on outdoor surfaces; you can't avoid it. Add water and you have a *somewhat* conductive situation at the end of the antenna, which
is ALWAYS a high voltage point. There is nothing good about that situation.

A good quality end insulator will minimize problems over the Long term. The larger eye in a proper insulator can also provide some increased mechanical reliability.

The cheapest way is rarely the BEST way to make something........  

( .......how much money are we talking about here??.....$7 if you get "expensive" commercial end insulators??  .....and you can make excellent quality
   insulators for a few dimes worth of material !!   The benefit to cost ratio on end insulators is extremely high.....  )
                                                                                              

73,  K0ZN
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