[Boatanchors] Beam elements

[RAY FRIESS]

Wayne:

 

You are correct in how you picture it.  The traps do have extensions on the end, as well as a capacitive hat of four spokes.

 

I realize that the homebrew 20 meter antenna with these traps would still be longer than the triband beam with the traps added, but the antenna would still be shorter than a half wave 40 meter antenna.

 

A half wave 40 meter dipole is roughly 66 feet long, end to end.    The triband driven element with the add on kit would be much shorter than than, of course.   But, even though the homebrew 20 meter antenna with the traps and loading hat and extensions would be longer than the tribander with the add on kit, it would still be shorter than a half wave dipole.

 

It sounds like, though, that the theory of operation and construction that I was thinking about is viable.

 

 

Ray
 
> Date: Wed, 13 May 2009 00:06:55 -0400
> From: hwhall at compuserve.com
> To: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Beam elements
> 
> > I have the traps that were made to add 40 meters 
> > to the driven element of my triband beam.
> 
> If I am picturing this correctly, you have a 10-15-20 beam for which you
> have a kit that adds onto it, to make the driven element a 40M dipole. The
> director & reflector elements won't do much of anything for the radiation
> pattern at 40M unless they too have add-ons, so the result is essentially
> just a rotating 40M dipole.
> 
> I expect the kit consists of 2 traps and 2 lengths of element to extend the
> length of the driven element past these new traps. The traps in the kit
> will be resonant at 20M in order to electrically "cut off" those 40M
> extensions when operating the tribander on 20M. They really are 20M traps
> therefore.
> 
> > I was looking at them the other day and thought using them 
> > to construct a rotatable dipole for 40 meters might be worth
> > experimenting with. 
> 
> You can use them but they are not resonanat on 40M and will only act like
> small loading coils at 40M. You might make better loading coils on your
> own, depending on how short you want to make the 40M dipole. Remember that
> all the other traps on that 20-15-10 driven element were also to be acting
> like loading coils when the triband antenna was set up and used on 40M.
> Therefore a shortened dipole you make with those 20M traps will be a lot
> longer than the tribander's driven element would be if it were set up with
> the 40M kit.
> 
> > if I made a 20 meter half wave antenna out of tubing or wire, 
> > and used these traps that maybe I could get the homebrew antenna
> > to resonate on 40 meters, as it would do if I put them on the 
> > driven element of the tribander 
> 
> Yes, you can make a 20M dipole, tack these onto that, and add wire beyond
> the traps, to make a 20M & 40M dipole, or 20M & 80M, etc. The traps will
> let the homebrew antenna operate as a 20M dipole and then act like loading
> coils to shorten somewhat the length of the dipole antenna at a longer
> wavelength. Note that adding the traps onto the ends of the 20M dipole will
> alter its electrical length somewhat from the textbook dipole length
> (changes the wire "end effect") and you'll have to tweak the 20M length a
> bit to compensate.
> 
> > I could manage such a rotatable dipole, where it would be 
> > too unwieldly to add them to my tribander.
> 
> Again, the 40M dipole you'd end up with will be a lot longer than would be
> the tribander if was set up with the 40M kit, because your homebrew 40M
> dipole won't have the 10M & 15M trap coils acting as additional loading
> coils.
> 
> --Wayne
> WB4OGM 
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