Re: [TowerTalk] Towers and Open Wire Feeder

["Rob Atkinson, K5UJ" <k5uj@hotmail.com>]

In the early days of balanced rotatable antennas (quads, yagis, LPs) hams 
fed these directly with open wire because coax was either not developed or 
not freely available.  The problem of getting around the rotation point was 
of course the sticky part and I had the solution explained to me once by one 
OT but unfortunately, I didn't mentally file it because I thought I'd never 
need to know it.

I would nevertheless consider feeding your antenna directly with the window 
line, or ladder line because it is after all, a balanced antenna, and you'll 
be free of baluns at the antenna, with no need for worry about mismatch and 
swr--just tune the shack end of the line with a balanced transmatch.

There is one important thing to remember however, and that is that your 
rotation will probably be limited to 180 degree arcs left and right of the 
point where the antenna feed point and the line are on the same side of the 
tower.  That's okay in that you'll cover all compass points, but trying to 
get the line to follow the antenna for a 350 degree rotation for example, 
may be asking too much of the system for keeping the parallel line away from 
the tower.

here's one idea for getting the line around the rotator:  you have your line 
coming up one of the tower faces on 2 or 3 foot standoffs (one every 10 feet 
or so) and at the top of the tower, at the last standoff, you enclose your 
feedline in a plastic hose with enough slack to form a 1/2 helix from the 
top standoff to the antenna feedpoint, when the f/p is 180 degrees opposite 
the top standoff.  when rotated back -180 degrees, it should loop out with 
the hose giving the feed enough rigidity to not sag down upon itself.   
you'd have to get the distance from the top standoff and the length of the 
feed and hose right to make this work so you have the right combination of 
length, and a happy medium between stiffness and slack so the feed stays out 
away from the tower but will move with the rotator.  you could close the top 
of the hose (or plastic duct) and leave the bottom open.  you would want 
material that would not breakdown in sunlight and wx.

maybe someone on the reflector who has been around long enough, can recall 
how parallel balanced feed was routed around rotators.  I'll admit my 
aversion for baluns may be somewhat irrational.

73,
rob / k5uj

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