[Moon-net] 2M EME coax routing

[Edward R. Cole]

At 08:19 PM 12/13/2006 -0500, Bob Baker wrote:
>
>Dear Moon-net,
>
>I am wondering if it is worthwhile to reroute the coax on my 2 antenna
>system, and would appreciate the consensus opinion of moon-net.
>
>Currently the coax is routed along the bottom of the booms, forward from
>the driven, to approx 6 inches from the cross boom, then down to the
>power divider on the mast, with a bit of slack. I have heard from a
>number of good sources that the "right" way to route the coax is
>straight down from the driven elements, then over to the power divider.
>
>My problem is that I suspect that the "right" way will not be right for
>me. It is fine when my antennas are horizontally polarized, but I
>mechanically rotate polarity. If the coax were hanging down from the
>driven, if I rotated to vertical, the coax would be next to, and
>parallel to the driven, perhaps even touching. This does not seem like a
>good idea to me.
>
>I suspect that I should reverse the connectors on the antennas and route
>the coax along the bottom of the boom to the back end of the antennas,
>past the reflector. Then drop the coax to the power divider.
>
>Two questions- is that the right way to go, and how many tenths of a db
>performance improvement should I expect compared to the current
>configuration?
>
>Thanks!
>
>73,
>Bob
>KD3UY

Bob,

Since you have essentially a single-polarity array and physically rotate
the antennnas, it probably does not affect your antenna pattern running the
coax as you describe.  For those of us running X-pol (crossed element)
yagis, the Vertical support masts are non-metallic to avoid pattern
distortion, therefore the only solution is to run coax lines back of the
reflector element and then up a light-weight support tube tying the rear
ends of the yagis together.  The coax then crosses on a tube parallel to
the main crossboom  where many place their dividers.  The main feedline
then runs to the center of the crossboom on another tube.

I have made a variation of that routing where I run a diagonal tube from
the mid-point of the vertical support mast.  The diagonal runs to a point
either side of the elevation bracket on the center crossboom where my
dividers are mounted.

This is pretty hard to visualize with words so go to my website to veiw
photos of the array.

On my four 3WL x-yagis (12x12 foot H-frame) each phasing coax line is
18-foot with approx. 0.25 dB loss using LMR-400.  Running with all right
angle tubes would extend the length of the lines by about 5-feet.  A small
reduction in line loss.

A structural advantage is gained as the diagonal tubing braces the array
much more than using all right angles.
73's,
Ed - KL7UW  
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