On Mon, 1 Aug 2005 17:43:34 -0700, "greg knapp 5"
wrote:

I need your advice, as I have never worked with open wire lines before.
I need to feed many different antennas with open wire line and need to run
the feeline from each about 200 feet from the back pasture to the shack. I
don't want to walk out 200 feet and throw knife switches to chose the
antenna/feedline I want to feed, so I plan to run separate 600 ohm open
feeds for each antenna all the way to the shack.
The problem is I don't know what the effect is or how to handle the
multiple open wire feed lines, as they will be parallel for probably 150-200
feet. I haven't found anything in literature describing this.
For instance, will they interact? how far do you space the feedlines from
one another? If I have 4 feedlines, can I stack them vertically or
horizontally one foot apart from each other? How much is enough separation?
What other precautions do I need? Need they be twisted if they are not near
anything other than the other feed lines?


I probably have more questions than answers.

1. Are the antennas to be operated independently? Is this a duplex or
diversity system?

2. Will the unused lines be terminated in the shack?

3. Are these multiband antennas with tuned feeders or could they just
as easily be coax-fed?

4. What do you consider to be detrimental interaction?


As others have suggested, there will be coupling between the antennas,
so feedline-to-feedline isolation will not necessarily be a figure of
merit.

If you consider the impedance change of a single pair of wires
operated over ground as a proxy for interaction, then with separation
by 3 or 4 times the wire spacing, you are probably okay for all but
the most critical situations.

One test would be to excite one line and measure the power in an
adjacent line, remembering that some (a lot?) of the coupling will be
antenna-to-antenna and will also be frequency dependent.