How to improve Dual band Slim Jim ?

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perseus68

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Hi all

After reading many threads of Slim Jim, J-poles and so on I ended up with the scheme attached.
I'm wondering if I could attach another half wave section, identical to the first one, on top of it.
Could that be separated (and phased) by a half wave (at 145MHz) stub made of coaxial cable and thus shortened by the appropriate velocity factor (typically 0.66)?

All suggestions are welcome

73s
EA8012SWL - Marco
 

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LtDoc

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Then you would have a two 1/2 wave array. Would it do 'better' than a single 1/2 wave antenna? I would think so. The 'trick' would be in the phasing line/stub. You'd have to be able to accurately measure that so hope you've got an analyzer.
- 'Doc
 

LtDoc

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This isn't exactly the same thing, but it's close, sort of. Basically just a typical 'J'-pole with a modification or two, which typically means an 'evening-out' (more symmetrical) radiation pattern. Commonly called a 'Ghost sleeve 'J'-pole'. Instead of just one short stub on one side of the thing, you add three more evenly spaced around that central long part. Doesn't add any 'gain' to anything, just 'regularizes', makes the radiation pattern more symmetrical. Gives you a full 369 degree pattern rather than one that has a sort of 'null' in it.
So, if you add a phased element or two to it, it turns into a vertical array type of thingy and does give some gain. It starts to get sort of 'complicated' mechanically, but isn't really all that hard to make.
Oh well, just an idea...
- 'Doc
 
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