Thanks for all the replies!

It sounds as though if I keep "short_rope" over one wavelength in length
(which I can do), that would do the best job of minimizing loss.

73's de Robert / N4IXT

"Paul Keinanen" wrote in message
...
On Sun, 15 Aug 2004 21:50:24 GMT, "N4IXT"
wrote:


I'm thinking of putting them side by side on the rope, as I have a lot of
space between the trees. Something like:

Tree--Rope--20m--short_rope--10m--Rope--Tree

In the _far_field_ the dipole would have a null in the direction of
the wire and thus, the connection between the dipoles would be
minimal.

If short_rope is much less than a wavelength, there are going to be
some near field influence on each other. Looking at the 14 MHz dipole
and ignoring the 14 MHz feedline for a while, there are two 5 m long
elements that are a half wavelength on 28 MHz, thus they are resonant
at 28 MHz.

...5m_section--X--isolator--Y--5m_section--short_rope--28MHz_dipole...

Since power is transferred via the near field, these two sections will
also reradiate and will work as additional point sources distorting
the radiation patterns into some directions. Depending on how tight
the coupling is between the 14 and 28MHz dipoles, this might or might
not be a problem.

Now look at the two 5 m sections of the 14 MHz dipole at 28 MHz. There
is a feedline connection at the right end of the leftmost section (X)
and also at the left end of the rightmost section (Y). Since the ends
of a half wave segment are the high impedance points and if some lossy
low impedance feeding arrangements as used (such as baluns, coax and
unpowered transmitters), some of the 28 MHz power transferred to the
20 m dipole is dissipated in these losses and not reradiated. This
will clean up the 28 MHz dipole pattern somewhat, but some transmitter
power is lost as heat in the 14 MHz dipole feed system.

A balanced open wire feed to the 14 MHz antenna with open circuit in
the shack should have minimal effect on the losses on 28 MHz, since
the power would simply be reflected back from the open end and
reradiated later on.

Paul OH3LWR