On Sat, 30 Jan 2016 12:04:49 -0000, "gareth"
wrote:

One of the problems with beams is the cable winding around
the mast if you try to turn too far in one way or another.

These difficulties have long been solved in the world of radar,
so, has anyone conceived of an infinitely rotatable 50 ohm
coupling for our beam antennae?

Clearly there would have to be some mechanical support other than
just the co-axial coupling to withstand the wind storms that we are all
now experiencing?

"Slip rings".
https://www.google.com/search?q=slip+ring&tbm=isch
https://www.google.com/search?q=coaxial+slip+ring&tbm=isch

For coax cables, it's a "rotary joint".
https://www.google.com/search?tbm=isch&q=rf+rotary+joint
I like to use a balun to go from coax to a parallel transmission line,
then to slip rings, and then to a dipole antenna feed. I once built a
direction finder that used a rotating yagi antenna, using that method.

As amdx mentioned, RF power levels are going to be a problem. My
interest is in direction finders, which normally do not transmit. If
you're going to run RF through the rotary joint while rotating the
antenna, the RF is going to arc and burn a nice neat groove in the
contact area. If the rotary joint is locked in place, it might
survive at low power levels.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558