Hello Sante,
As I recall from a triband wire vertical project, the higher
band elements needed to be LONGER than normal due
to interaction effects.
One of my favorite WARC band antennas is a 20M dipole
(34 ft total length) fed with ladderline and a balanced antenna
tuner. This provides a figure 8 pattern from 10 through 30M
with beamwidths from 50 degrees on 10M where it acts as
two half waves in phase to 90 degrees on 30M where it is a
short dipole (2/3 size).
Performance on 30M could be improved slightly by using a
40 ft center fed dipole instead which will be two half waves
on 12M (and 1.25 WL on 10M as a double extended Zepp).
de Tom N4KG
On Mon, 01 Oct 2001 Sante - IK0HBN <ik0hbn@libero.it> writes:
>
> Hi,
> I need your help. I must redo 2 dipoles hanged down to the same
> coax. They
> got broken due to the age of wires, so I choice using thicker wire.
> Involved bands were 30 and 17 meters. Having to do the job I have
> thought
> adding even the 12 meters band so to have that band running here. My
>
> questions are:
> a) Is it possible sharing a single balun for 3 dipoles? I guess YES.
>
> b) Have I trying trimming them when ALL linked to the balun, or
> should I
> cut one dipole at time, removing it, and after putting up another to
> be
> trimmed?
>
> c) If the first option should be preferred, of course trimming one
> band
> legs, resonance on the other 2 bands will move, so from which band
> I have
> to start trimming? IE. Do I begin bringing at resonance the 30
> meters band
> first with the other 2 at place (linked to balun) or should I start
> from 12
> meter? - My question take place from the evidence that cutting one
> band,
> the others two move enough.
>
> I have a MFJ-269 for the job.
> From the balun the 3 dipoles run slightly separated so to have them
> at
> ground about 1 meter between them.
> Any possible help/hint will be greatly appreciated here.
> TIA
> Sante
>
> --
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