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Author Topic: 10 meter J-Pole?  (Read 3199 times)
KE6BGH
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« on: January 26, 2001, 06:47:06 PM »

Anyone usign a J-Pole on 10 meters?  It looks like it could be practical (24 to 26 feet long, or so).  I have been looking for a construction article, but it looks like I will need to build one and then write an article.

There are a few sets of measurements floating around, but they appear to be extrapolations from VHF j-poles, sometimes just by multiplying the measurments by the frequency ratio.  I don't trust this necessarily, unless the element diameter is increased also.  I would rather not use 2.5 or 3 inch copper pipe.

Anyone with experience operating a 10 meter J-Pole?

I hate re-inventing the wheel, especially when silver-soldering copper pipe....

Thanks,
Dave Smith
KE6BGH
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WB6BYU
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Posts: 13016




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« Reply #1 on: January 29, 2001, 12:21:47 PM »

The first J-Pole I ever built was for 15 meters (using 300 ohm
twinlead).  There are commercial J-pole antennas for 10m (and I've
seen some similar CB antennas over the years.)

However, I would recommend using aluminum tubing instead of
copper pipe for the longer lengths.  Besides greater strength and
less weight, you can telescope sections to make adjustable length
elements.  Many hardware or home-improvement stores sell
aluminum tubing in 6' or 8'  lengths.  (Actually, any metal mast or
conductor 25' long or more can be made to work.)

The most important dimension from a mechanical perspective is the
radiator - the portion of the long element above the top of the short
element.  This should be a half wavelength:  16.5' for thin elements
like wire, or 16' for 1" or larger tubing, will be close enough.  The
matching stub (the short element and the corresponding part of the
longer element) will be around a quarter wavelength (say, 8 1/2")
but this length should be adjustable to accomodate other variations.
The spacing between the elements, and their diameter, is not
important.  Use whatever is convenient and practical mechanically.

You probably will want some sort of insulating spacer between the
elements.  This should NOT be at the top of the stub, where the
RF voltages - and therefore losses - will be highest.  I would shoot
for somewhere like 5' to 6' above the bottom of the stub.  A thick
piece of polycarbonate clamped to each element should work.
At the bottom of the stub, you want some sort of adjustable shorting
bar, such as a piece of aluminum bar or channel stock with a U bolt
to go around each element.  Start with this about 8 1/2' below the
top of the short element.

The feedpoint will vary, depending on the feed method.  I've had
best luck with a 4 : 1 coax balun, with matches higher up the stub
than direct 50 ohm feed.  Use a couple cable clamps or whatever
to connect the ends of the feedline to the elements in such a way
that you can slide them up and down the stub.  A starting point
might be 8" above the shorting bar.  Then adjust the feedpoint and
shorting bar positions for minimum SWR.

Good luck ! - Dale WB6BYU
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KE6BGH
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« Reply #2 on: January 30, 2001, 02:14:20 PM »

Thanks, Dale!

Maybe I will actually do some experimenting and write something up for the Article section on EHam.

I have been thinking since I made the first post, and maybe some aluminum conduit would be strong enough.

I'll just have to start cutting and trying.

73s de Dave, KE6BGH
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N1LO
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« Reply #3 on: June 08, 2001, 03:17:59 PM »

I have plans for a 10m and 20m wire J-poles at:
http://www.qsl.net/n1lo/antenna.htm

Happy building!

--...MARK_N1LO...--
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