[Antennas] MODIFYING_TRIBANDER_BEAM

[Billy Cox]

>Since the elements are not long enough for a dipole on 20 meters
>does the traps add some loading on 20 so as to allow a shortened
>20 meter element?

Yes ...

>Do they also allow for a shortened 15 meter section as measured
>between the two traps on an element?

Yes ...

>Is there any formula to estimate where the traps should be placed 
>out on the elements when wound for 17 and 12 or 15?

Look in the older ARRL Antennas handbooks ... the "original"
design was sometimes called the DZZ <W3DZZ?> as I recall,
but it's been MANY years ... so not extra points for accuracy! B-)

>I can't see any problem re-winding the traps at will for any frequency
>I want between 17 and 10 meters. I probably won't be much of a
>problem getting aluminum to extend the elements which I figure
>should needs to be done in order to re-do for 17 meters.

Let me toss out a couple of ideas ...

1. The older Hygain DB1015 <or similar, dang this getting old>
was a 3L 10/15m yagi ... that others reworked to use on 17/12m.

Digging out that article might give you some additional ideas
as to what to change, and how.

2. Before I would mess with the traps, I would take only the driven
element ... and play with changing ONLY the tubing lengths to see
if I could come up with a combination that used the existing values
of L/C in the traps. Or get as close as I could, and then modify the
traps. Trying to change too many variables at once <trap values
and tubing dimensions> might make for a disappointing project.

>I purchased the ARRL antenna book and tri-banders and traps
>are not covered to any extent to allow one to build their own.

Older versions had some limited amount of information, see above.

> In order of importance for my operating interests the bands are
>20, 17, 12, 15, and lastly, 10 meters.

Don't overlook using your existing tribander and just adding a
rotable dipole for only 17/12 above the existing tribander ... a
dipole up high is actually a very good antenna to use ...

Hope this helps ... and Happy Holidays to ALL!

73 Billy AA4NU