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Author Topic: fng with 2 meter jpole question  (Read 1072 times)
KK4NQL
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Posts: 3




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« on: January 16, 2013, 08:24:39 PM »

Hello! I'm a new ham... Here is my question. Can a copper 2 meter Jpole share the same space on a single mast @ 25 ft with an imax2000? I made a bracket to support the jpole and isolated it with tubing.  The bracket will be attached to the mast. Total coax run is about 35 ft of Lmr400. The antenna itself touches no metal. The Imax is offset at the top of the mast and I was going to install the jpole at the same height but at 180 degrees opposite and about 12 " apart from each other. This is just temporary until the tower goes up. The idea is to max out the height but I'm not sure if the Imax will impede the performance of the Jpole...  only one antenna will be used at any given time. Thx in advance for your input. Ray.
« Last Edit: January 16, 2013, 08:29:13 PM by KK4NQL » Logged
KB4QAA
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Posts: 2488




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« Reply #1 on: January 16, 2013, 10:37:49 PM »

Ideally, I would offset them vertically.  However from a performance perspective since the Jpole will be close to the metal mast if lowered, it is probably a wash, so having them alongside one another won't matter.  Just check and see if you have any interference on either radio from overloading, due to proximity.

bill
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WB6BYU
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« Reply #2 on: January 17, 2013, 08:36:19 AM »

Having another antenna only a foot away from the J-pole will likely change the
tuning and impact performance.

It might still work, though 2' or 3' of spacing between the two antennas would
be better to minimize impact.

If you put one above the other, the coax to the upper antenna will have to run
down along the lower antenna, which will change the behavior and tuning.

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KK4NQL
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« Reply #3 on: January 17, 2013, 09:22:03 AM »

Thx to both of you. I'm going with plan "B". Guy the mast and attach the jpole to the mast @20 ft on a 3 ft boom. The imax2000 @25' and the jpole below extended 3 ftt out at 90 deg to the mast. Your thoughts? Thx Ray
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N6AJR
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« Reply #4 on: January 17, 2013, 10:20:48 AM »

Remember too, that most of the time you will be using the Jpole to talk to a repeater, so not much antenna is needed, and it will probably be full quieting at 5  watts any how.
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N4CR
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Posts: 1701




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« Reply #5 on: January 17, 2013, 02:16:52 PM »

Because the feed point of a J-Pole is high impedance, they tend to couple into any near metal. Your j-pole needs to be out in the free and clear and fed through a choke to have it resemble the expected pattern.

A side arm with a vertical ground plane would be a much better choice since it has a low impedance feed point. A 2 foot sidearm with a homebrew quarter wave ground plane built on a SO-239 would perform normally.

J-poles come with a lot of issues. The can be difficult to tune, they couple into other metal in the vicinity, including the coax shield and they are larger than needed to produce an identical pattern. There seems to be a craze about j-poles that is unjustified.
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73 de N4CR, Phil

Never believe an atom. They make up everything.
N6AJR
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Posts: 9927




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« Reply #6 on: January 18, 2013, 10:48:14 AM »

you can mount a jpole abou anywhere and have it work ok. the base of  the Jpole is usually at ground potentialso bolt it to the side of the house somewhere and leave the tower to stuff that needs it.
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KK4NQL
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« Reply #7 on: January 19, 2013, 06:55:20 AM »

Well. The two meter is up and working well. Thanks for the input. I'm hitting distant repeaters and sounding good on simplex. This should do. And I will also follow the advise of the last post and leave it there . The tower space it's for the big yagis. Thx again for helping me out! Ray
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