[TowerTalk] Tower spacing

[Patrick Greenlee]

I have limited experience with towers (mostly for repeaters) and never had 
multiple HF towers before so I have a question before I boldly go where I 
have never gone before.  Are there any other considerations regarding tower 
separation I need to know about other than ensuring the towers are at least 
1/2 wave apart at the lowest operating frequency for which any of the towers 
has an antenna?    I think the 1/2 wave or more rule of thumb will ensure 
that the kill zone of any of the towers is less than their separation.  Only 
tower #3 could even get close to being a problem.  Vertical vs horizontal 
polarization?  Is this a big issue in deciding what is enough tower 
separation?  I realize there is a continuum and greater separation is likely 
better but for practical purposes how much is enough?  Plain language 
please.  Note:  I intentionally refrained from mentioning data values 
getting to within 1/e of their asymptotic value or such language.

I am not interested in a phased array, just relatively independent towers. I 
currently have a Hy-Gain Hy-Tower vertical mounted 23 ft above ground on a 
metal building/counterpoise, sans radials.  This antenna with the coming 
addition of a 160 meter mod will cover 8 bands. 160, 80/75, 40, 20, 17, 15, 
12, 10m.  (I don't do 30 and 60m yet.)   The 160m mod consists of a 40m trap 
attached to the 24 ft point (top of the triangular tower portion) and a 
nearly horizontal wire to resonate the combination on 160m.  I will run the 
wire basically off to the south of the vertical antenna and the three towers 
will be north of the roof mounted vertical.  I am using this vertical to 
support one end of a Carolina Windom 270 ft long.  The end of the wire is 
out on an insulating Dacron rope attached to the 24 ft level on the vertical 
antenna (about 47 ft above ground) spaced out about 15 ft to avoid coupling.

In addition to the Hy-Gain Hy-Tower 8 band vertical I will be installing 
three towers.
Tower #1 is a two section crank-up/tilt-over with a round mast welded on in 
the center of the top few feet which tapers down to the mast OD.  This tower 
is just about 41 ft (extended) from the bottom of the base section to the 
top of the tube mast.
Tower #2 is a free standing tilt-over composed of 5 sections totaling about 
50 ft.
Tower #3 is a free standing tilt over remote controlled raise/lower unit 
that has not been selected yet.  It will not be mounted on the ground but 
instead its base will be installed on a sturdy metal platform 40 ft above 
ground.

I have a fully assembled K4KIO hexagonal beam to put atop either tower #1 or 
#2. (Decisions decisions...)
I'm still struggling with antenna selection for Tower #3.

Whichever tower, #1 or #2, that gets the hex, the other will likely get a 
dual band vhf-uhf beam and a dual band omnidirectional vertical.

I may give consideration to stringing some skywire between these towers but 
not if it overcomplicates their placement.  The towers will be connected to 
the shack and to each other by buried conduit in a daisy chain configuration 
rather than a star or other coax gobbling configuration.  Remote operated 
coax switches will select the active antenna.  I do not envision the need 
for being able to use more than one antenna at a time so coax sharing seems 
practical.  Receive only antennas may become part of the switch matrix 
consideration.

Any assistance will be appreciated (here or via PM.)

73,

Patrick AF5CK