On 10/25/2010 06:31 PM, John Ferrell wrote:
It looks like I am going to have the resources to install a second
antenna tower. I never thought it would work out this way so I have
not planned it as I put other things in place.

The question is: How close is too close?

I know more separation is better and I doubt I can predict the future
well enough to model expected configurations.

The first in place is the existing crank up mast with power winches
that allow me to lay the whole works down for maintenance. HF tri band
in place at about 55 feet.

About 50 feet north of that tower is my field of 36 radials where I
currently have a 40 meter self supporting vertical. I would really
like to not compromise the radials or the operation of whatever
vertical I choose.

I am thinking of putting the "new" tower about 20 feet West of the
vertical& radial field. The plan calls for 4 sticks of Rohn 25 on a
tilt plate with a utility pole doing the stabilizing. Winches as
required.

That is a little more co ax than I would like, but my real concern is
whether this will be a major hit for the vertical and other antennas.

I would appreciate any thoughts and especially experience.


John Ferrell W8CCW

Hello, and just to tack on to the other comments: If the second
antenna's presence changes the feedpoint impedance of the first antenna,
you can be sure the second antenna is in the induction (close coupling
(non-radiating)) field of the first antenna. If the second antenna
could be located about 2-3 wavelenghts from the first it would be in the
far-field and its contribution to the radiation pattern of the first, if
any, would be minimal. Alas, since this might not be practical, perhaps
some modeling using NEC/EZNEC prior to antenna installation would allow
for some optimum trade-offs regarding parasitic effects introduced by
the second antenna with the goal of saving time (and money). Sincerely,
and 73s from N4GGO,

--
John Wood (Code 5520) e-mail:

Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337