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Old 11-08-2008, 15:20   #1
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Optimal length for radiating element ?????

I am about to install an insulator in my shroud for SSB operation and I am trying to decide what the optimal length should be "in my case".
I use pactor a lot on 80m & 40m and I also like to operate on 20m a lot, as well as all the marine frequency's. I realize the radiation pattern is not very good above 20m so I am not too concerned about frequency's above 20m, but I would like my antenna to be most efficient on 20m and below. To supplement this antenna I plan to build a vertical dipole for 20m operation and maybe some other dipoles for the higher frequency's. But as my shroud will be my permanent antenna I want it to radiate with maximum efficiency on 20m and below. I realize the longer the antenna is on frequency's below 30m the better it will radiate, but I am thinking if I optimise it for 20m the shortening in length will have minimum impact on the lower frequency's? I was thinking to make the radiating length of the shroud 42 feet (12.8m). I have an extensive ground system using resonant radial ground wires and an auto tuner. Would any body like to comment on what they think the optimal length my radiating element should be?
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Old 11-08-2008, 16:24   #2
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42' sounds like ballpark, but it's very hard to say without modeling.

Might I suggest that you rig a temporary antenna made of whatever material you have readily available and try different lengths? You won't be able to duplicate what the shroud will be unless you remove the existing shroud and use comparable material (probably totally impractical), but you might get a close approximation by rigging the temporary antenna just forward, aft, or outside the shrouds, using PVC standoffs as necessary.

Certainly worth a try, I'd think.

BTW, I assume you're just gonna add ONE insulator at the top, and feed the shroud from the chainplate bolts belowdecks, right?

Good luck,



PS...nothing, but nothing will equal a 20m vertical dipole, so I hope you build and try one early on. If you have one, then you won't worry so much about 20m with the shroud -- which in any case ain't gonna be great -- and could optimize it for lower bands :-)

Be sure to check out this thread: Black Box Secrets - Revealed!

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Old 12-08-2008, 19:08   #3
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Hi Bill,
Thanks for your comments and it's good to know I am on the right track. (I think?)
Yes you are correct I plan to just install one insulator and feed the shroud above the lower turn buckle.
Although I plan on using a vertical dipole for serious 20m work, I would like to optimise the shroud for 20m for passage making, inclement weather and for when I am too lazy to rig up a temporary vertical dipole.
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