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Author Topic: tri band j pole  (Read 3949 times)
KC9PNN
Member

Posts: 13




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« on: October 01, 2012, 07:53:31 PM »

wear can i find plans for a tri band j pole  Smiley
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tim kc9pnn
K5LXP
Member

Posts: 4536


WWW

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« Reply #1 on: October 01, 2012, 08:05:54 PM »


http://www.google.com

Mark K5LXP
Albuquerque, NM
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WB6BYU
Member

Posts: 13573




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« Reply #2 on: October 02, 2012, 08:55:50 AM »

Which three bands do you want?  160m + 2m  + 5.5 GHz?

Sometimes you have an application that is uncommon enough that nobody who has
come up with a solution has documented it.  (And just because someone has published
a design doesn't mean it actually works very well.)  In that case you have to start
from basic principles and build you own.

The ARRL Antenna Book used to have a design for a 6m / 2m / 440 J-pole.  It used
a single radiator with each matching stub built on the side of it and the coax cables
for the upper antennas running down inside the radiator.  You can use that approach
for other bands:  the distance from the top of the radiator to the top of the matching
section will be 1/2 wave on each band (though that might have to be adjusted somewhat
to account for the matching sections on the higher bands, but it is a good starting point.)
Then each matching section will be about 1/4 wavelength long:  to allow for adjustment,
make it somewhat longer than that (perhaps 3/8 wave) and provide a sliding short to
adjust the electrical length.

Then, on each band, adjust both the position of the feedpoint tap on the stub and the
length of the stub (the shorting bar) for minimum SWR.


J-poles, however, are not the perfect antenna, and are prone to stray currents on the
coax and/or mast.  Something like a discone may be more suitable for multi-band operation.
The J-pole has no gain over a dipole, and very little over a groundplane, and there are
other options that may be easier to build for multiband operation.

Depending, of course, on which bands you want to cover.
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WB2WIK
Member

Posts: 20666




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« Reply #3 on: October 02, 2012, 10:15:36 AM »

Which three bands do you want?  160m + 2m  + 5.5 GHz?

I need some help with my 160m j-pole.  Turns out the longer pole is 390 feet long and the FAA says I need to place a beacon light at the top.

When I added the light, the pole started to bend from the added weight.

Should I go to Rohn 55G tower for that pole? Wink

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WB6BYU
Member

Posts: 13573




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« Reply #4 on: October 02, 2012, 10:59:40 AM »

Build the J-pole with a very pointed tip and run high power to generate a corona.
That will discourage aircraft from getting too close...
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KF7NUA
Member

Posts: 153




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« Reply #5 on: October 02, 2012, 11:58:27 AM »

Which three bands do you want?  160m + 2m  + 5.5 GHz?

I need some help with my 160m j-pole.  Turns out the longer pole is 390 feet long and the FAA says I need to place a beacon light at the top.

When I added the light, the pole started to bend from the added weight.

Should I go to Rohn 55G tower for that pole? Wink



I am having a bad day today but when I read this I smiled and felt better, thanks for the lift.....  Smiley
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N8CMQ
Member

Posts: 403




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« Reply #6 on: October 02, 2012, 03:10:01 PM »

Build the J-pole with a very pointed tip and run high power to generate a corona.
That will discourage aircraft from getting too close...

Turn it into a Tesla coil and scare the bejesus out of everyone!
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N8CMQ   Jeff
KC9PNN
Member

Posts: 13




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« Reply #7 on: October 02, 2012, 06:42:54 PM »

it would be use on 2meters 440 and 220
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tim kc9pnn
KE5PPH
Member

Posts: 73




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« Reply #8 on: October 02, 2012, 07:02:09 PM »

Build the J-pole with a very pointed tip and run high power to generate a corona.
That will discourage aircraft from getting too close...
  They call those bug zappers and can be had, at any home big box store. Grin  ever seen an ultra light in the power lines.
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WB6BYU
Member

Posts: 13573




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« Reply #9 on: October 03, 2012, 09:01:08 AM »

Quote from: KC9PNN

it would be use on 2meters 440 and 220




A J-pole is generally NOT a good choice for a multi-band antenna because the matching
stub should be 1/4 wavelength, and that only happens on one band.  Sometimes you can
manage 440 MHz on a 2m version because it can work with a 3/4 stub, though the tap
point will be a compromise between the two.  But adding 220 isn't particularly practical
unless you have some way to adjust the stub length remotely.

A discone or some sort of biconical arrangement, or a ground plane with separate
elements for each band, is probably a more practical approach to cover those bands.
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