If, on each side of the feed point, a single conductor runs out
to point X, with individual conductors onward from X for each
band of interest, how far from the feedpoint can X be?

(like this) /10 meters
/
FP----------------X------15 meters
\
\
\
\20 meters

--
-fb-

On Wed, 13 Sep 2006 15:46:07 -0500, funkbastler
wrote:

If, on each side of the feed point, a single conductor runs out
to point X, with individual conductors onward from X for each
band of interest, how far from the feedpoint can X be?

(like this) /10 meters
/
FP----------------X------15 meters
\
\
\
\20 meters

Hi OM,

Good question. One that the free version of EZNEC should handle.
Given that X can vary considerably (and only you know where you want
to start), there must be a multitude of right answers. Also, each of
those multitude of right answers is probably going to have unique
lengths.

73's
Richard Clark, KB7QHC

funkbastler wrote:
If, on each side of the feed point, a single conductor runs out
to point X, with individual conductors onward from X for each
band of interest, how far from the feedpoint can X be?

(like this) /10 meters
/
FP----------------X------15 meters
\
\
\
\20 meters

If this worked, we wouldn't need trapped tri-banders.

A 10m signal at X will test the three possible paths
and take the 20m one because it is a lower impedance.
The two shorter ones have very little effect at any
frequency.

The reason that real fan dipoles work is that the 10m
signal sees a low impedance at the feedpoint which is
not the case above.
--
73, Cecil http://www.w5dxp.com

There's no fixed limit. The closer together the conductors are, the more
they'll couple. The coupling has two major effects. First is that the
resonant length of one wire will depend on the lengths of the others; in
particular, shorter ones will be affected by longer ones. So tuning will
be tricky and somewhat interactive. The other is that the antennas will
be more narrowbanded than when the wires are separated farther. So you
get to choose whether to space them closer and have the effects of
increased coupling, or space them farther apart and have them be more
independent.

Roy Lewallen, W7EL

funkbastler wrote:
If, on each side of the feed point, a single conductor runs out
to point X, with individual conductors onward from X for each
band of interest, how far from the feedpoint can X be?

(like this) /10 meters
/
FP----------------X------15 meters
\
\
\
\20 meters

Similar to the Hustler models of mobile antennas, the distance between FP
and X would be part of each dipole. FP would be the end of the coax
connected to the dipoles.

Bill, W4WNT


"funkbastler" wrote in message
...
If, on each side of the feed point, a single conductor runs out
to point X, with individual conductors onward from X for each
band of interest, how far from the feedpoint can X be?

(like this) /10 meters
/
FP----------------X------15 meters
\
\
\
\20 meters

--
-fb-

W4WNT wrote:
Similar to the Hustler models of mobile antennas, the distance between FP
and X would be part of each dipole. FP would be the end of the coax
connected to the dipoles.

There's a big difference, Bill. With the Hustler system, the
10m *loaded* element has a lower impedance on 10m than the 15m
and 20m elements, so most of the 10m energy flows into the 10m
element.

Without loading, as below, the 10m element has the highest
impedance on 10m. The 20m element has the lowest impedance
on 10m so most of the 10m energy flows into the 20m element
and the system is non-resonant on 10m.

I used EZNEC to make a vertical inverted-L, resonant on 20m.
It has a 6 foot vertical section and a 10.8 foot horizontal
top section. Then in the other direction at the top, I added
a 2.25 foot section to try to make it resonant on 10m. There
is very little 10m current in the 2.25 foot section. Most
of the 10m current flows in the 10.8 foot section. The
feedpoint impedance on 10m is 522-j719.

On 10m, the impedance looking into a 10.8 foot whip is much
lower than the impedance looking into a 2.25 foot whip.
The 10m energy pretty much ignores the 2.25 foot whip and
takes the path of least impedance into the 10.8 foot whip.

"funkbastler" wrote in message
...
If, on each side of the feed point, a single conductor runs out
to point X, with individual conductors onward from X for each
band of interest, how far from the feedpoint can X be?

(like this) /10 meters
/
FP----------------X------15 meters
\
\
\
\20 meters
--
73, Cecil http://www.w5dxp.com