The j-pole antenna is fixed...

https://www.amazon.com/Shakespeare-...ords=marine+VHF+antenna&qid=1595345917&sr=8-4
Just cough up the $50 and be safe!

 

If a 1/2 wave has more gain than a 1/4 wave due to a narrower vertical pattern, wouldn't the boat healing reduce the effectiveness of the 1/2 wave?
Thanks
Joel

 

That's a good question especially for single hull sail boats. I'd say the patterns of both are so broad and similar that this won't matter for all, but the most serious angles. Here is a comparison (measured) of two 1/4 wave approaches with a J (half-wave)...

I think the takeaway here is boat healing, while an important consideration, won't be a big deal until you have some collinear gain of some sort. Here's an example where antenna tilt begins to matter. Your question is perfectly reasonable. I think we are reasonably safe with either a 1/4 or 1/2 wave vertical antenna with respect to boat healing.

 

Thanks.

In your reference, it looks like about 30 degrees (or so) angle of heel, there would be nulls. I'd love to see the real effect on range of different antennas on sailboats, given that height is probably the dominant factor in range and a larger antenna puts weight at the top of a mast and affects the boat itself.

For example compare a duckie that's mounted just under the masthead light (lets say 30' to 45', and a 5/8 wave mounted 6' above the water (with either a gimbel mount or hard mounted), at 30 degrees of heel or so (which would only affect the non gimbel-ed antennas).

Not that any of this matters to me, I'm more of a canoe person, but it's a god thought exercise.

Thanks
Joel

 

Never been a fan of this design to begin with, less so of the occasionally ludicrous performance claims.

That said, it seems like someone didn't research this well when it comes to patents. As mentioned by others, decoupling of a J-Pole isn't anything new, nor is feeding the feed-line inside the copper. But then we seem to be talking about a government agency so... whatever.

 

AEA did it with the Isopole antenna they sold decades back.

 

Although I think a more accurate description would be in the
23rd edition of the ARRL antenna book. Figures 16-11. where the mast IS the feedline.

It's a little confusing the way the antenna book (and hams in general) describe things as "impedance transformation" which is a very non-visual way of describing what is happening.

Sometimes hams have a funny way of viewing and stating things,

/Rant on
like a portable radio being something that is transported in a vehicle, and a mobile radio being something that is hand carried.
/Rant off

I was taught to visualize it as looking at a 1/4 wave stub that is shorted at its end, and drawing a sine wave along it, the short is where the zero crossing was, flowing back 1/4 of the sine wave shows an open being "forced" on the line.

Figures 24-16, or 24-19, of the 23rd edition show more sophisticated uses of the 1/4 wave stub that are clearer than the RADAR references that I used earlier (mostly the same idea though).

Thanks
Joel

 

Well, hello there to you all, I don´t know but I do still enjoy very much the antenna building stuff, as a matter of fact, my prefered scenario is the roof from let´s say 8 am! ;D And very much likely so, I´m gonna build me one of this decoupled J-pole. just for the fun of it, but of course I won´t tell anyone! 73´s

 

The patents are for the US and its territories only. Have at it and let us know how it goes.

 

That's one of the primary points of the patent... to document, permanently, the issues along with a novel solution to those problems, hence reinforcing the problems really do exist. This is documented in a system that makes the resulting research available to the public rather than buried behind the paywall of the IEEE or equiv.

Who didn't research it? Me?

Perhaps so and I welcome evidence that the combination of techniques presented in the patent preexists the patent. I looked hard, documented references aplenty in the two patents (unusual for patenting), and found no published solution matching the claims. Make no mistake though... the burden of proof no longer rests with me after issuance of the patents. So please... back up your assertions with hard preexisting published evidence.

Because I work in antenna engineering in a gov. lab has little to do with anything.