[Boatanchors] Beam elements

[H.W.Hall]

> 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