You'll have better isolation between systems if you mount all three 2M
antennas on the same mast, directly above/below each other. I'll recommend
19" spacing off the pole. Mounting one quarter-wave away from the reflector
is one of the easiest pattern changes to model; it gives a nice cardioid
pattern on 2M. The UHF side of the J-pole antenna will therefore be 3/4
wavelength from the reflector and the pattern on 440 will have three lobes,
much like a clover leaf.

I suggest using 1/2" CPVC Schedule 40 water pipe for both the vertical
support and the arms at top and bottom. That stuff is cheap, easy to cut,
and glues together very quickly - don't make any assembly mistakes! Put a
"T" fitting at the bottom to let both the coaxes and residual water vapor
drop out of the radome assembly.
--
Karl Beckman, WA8NVW


"Tom Horne" wrote in message
...
I am trying to find out how far an open stub, dual band, two meter and
seventy centimeter J-pole needs to be from a parallel metal support
mast on which it is side mounted to avoid detuning the antenna. I'm
not concerned about the effect on the radiation pattern as I can mount
the antenna on the side of the mast towards the area I'm trying to
cover. I have to build brackets to accomplish this mounting and I
would like to avoid building multiple sets of them just to test for
clearance. If anyone has the requisite skills and tools I would
appreciate any information that can be readily found by modeling this
antenna in proximity to a metal support mast consisting of four inch
aluminum tube. I have two AB-952 masts on which to mount six
antennas. Three of them will be two meter omnidirectional antennas.
Since we need two limit interaction and interference between the three
two meter stations We will be mounting one of these at the top of one
mast, one a third of the way up the second mast, and the third two
thirds of the way up the first mast. Both masts will be deployed with
extension kits so they will be fifty feet in total height.

In truth I just do not have the skills or the time to develop them to
do this so any help would be greatly appreciated. This is for a
public service event that is now only two weeks away.

--
Tom Horne, W3TDH