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Author Topic: Easy J-Pole Question  (Read 570 times)
KD0BIE
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« on: September 12, 2008, 10:59:34 AM »

This weekend my buddy and I are going to make a 2M J-Pole.  I have found many good instructions on the internet on how to make it, but I have one question not brought up on the websites.  What is the best way or how do I prevent the copper J-Pole from oxidizing?  Would some clear coast spray work?  And if so would that prevent the J-Pole from working properly?

Daniel
KD0BIE
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WA3SKN
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« Reply #1 on: September 12, 2008, 11:17:16 AM »

The J-pole is simply a 1/2 wavelength radiator sitting on a 1/4 wavelength "U shaped" shorted transmission line.
The shorted end is zero ohms, and the feedpoint is at a high impedance.  Somewhere between the zero ohm point and high impedance point is a 50 ohm point.  That is where you connect the transmission line.
The copper pipe can be grounded at the center of the "U" for lightning protection.  The copper pipe can oxidize with no ill effects.  You might want to weatherproof the coax connections.  Some people paint them, or protect them with a clear spray.
Some people add a ferrite "balun" on the coax to minimize radiation off the coax.
Good Luck on the project!
73s.

-Mike.
 
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WB2WIK
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« Reply #2 on: September 12, 2008, 11:17:58 AM »

Krylon Klear Coat or many other sprays (they don't have to be clear, either) will work fine.

However you don't really have to protect copper from the weather.  It turns green then kind of greenish black, and finally perhaps black but that doesn't prevent it from working just fine as an antenna.  

In fact, most people like the darker patine that copper develops outside, it takes off the "shine" and makes antennas much less visible.

WB2WIK/6
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N5LRZ
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« Reply #3 on: September 12, 2008, 11:43:18 AM »

As mentioned previously, you could spray the antenna with some of that clear varnish stuff, but why?

As long as your transmission line connections to the antenna are solidly made and the fittings are properly soldered a little age does no harm.

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VK1OD
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« Reply #4 on: September 12, 2008, 03:22:18 PM »


Daniel,

The reason why the antenna will not degrade with weathering of the copper is that the corrosion products of copper have good conductivity.

That isn't true of all metals.

Owen
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N4CR
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« Reply #5 on: September 12, 2008, 03:29:15 PM »

Don't get me wrong, I've made my share of J-Poles looking for the magic. But it's a lot of extra work and expense for an antenna that doesn't work any better than this one:

http://www.hamuniverse.com/2metergp.html

And in many cases, the ground plane works better.

You also might be interested in either of these sites:

http://hometown.aol.com/alonestaryank/DESKBUDDY.html

http://www.ac4rc.org/2M%20CPFL%20Antenna.pdf

Those are both portable antennas, but the designs are pretty cool and highly functional in a small space.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
WB9URN
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« Reply #6 on: September 12, 2008, 05:37:10 PM »

Why not a "slim jim". See this site..
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12033

Supposed to give gain, and as easy as J pole to build.

Must be mounted CLEAR of metal.
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KD0BIE
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« Reply #7 on: September 29, 2008, 07:40:21 AM »

I have one other question.  I have constructed and installed the J-Pole.  It works excellent.  More than what I thought it would do, but I have one question about after the installation.  After having it up for about a week I have noticed some corrosion forming at the SO-239 where the copper and that piece meet.  Will or could this be a problem later down the line and should I do something about it now?

Daniel
KD0BIE
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