Damien,
There is a general "rule of thumb" that suggests that open wire feedline
should be at least 4 to 5 times the feedline conductor spacing from
*anything* that is conductive. So, if your feedline is 1 inch in width
you want to keep it 4 to 5 inches from anything made of metal. Of
course, this would include another feedline.
There are two issues here:
1) If open wire line runs near something metal (conductive) and one of
the wires is closer to the metal than the other then the line will
become unbalanced at that point. This will cause the line to radiate.
2) If open wire line runs near something metal (conductive) and the
wires are equidistant from the conductive object then balance will be
retained but there will be an impedance bump on the line. This means
the line is no longer "flat" and will induce reactive components.
Issue #2 is of less concern than #1 so the second rule of thumb is that
when you must run your feedline near a conductive object you should try
to make the two wires be the same distance away from it. That will
retain balance.
Going through the pine trees is going to be fine if the feedline wires
are insulated. If the wire is not insulated more care should be taken
to ensure that it does not come in contact with anything. Even pine
trees become rather conductive when it rains.
Even with insulated feedlines you'll want to minimize physical contact
with the trees to the extent possible. Trees move and may eventually
degrade your feedlines.
73,
Doug, W7KF
http://www.w7kf.com
On 09/11/2013 08:45 AM, Damien Mannix wrote:
I have just been fortunate enough to obtain an MN-2700 with Balun.
Sorry if this is slightly off topic, and I hope it is not a silly
question, but if I feed an antenna 150 foot away with 450 ohm twin feed,
will it matter if it passes through two mature pine trees whilst on its
way? Also, if I want to feed two antennas can I run two 450 ohm twin
feeds beside each other or will they interact?
I have looked at endless antenna books but cannot find the answers.
Regards
Damien G3XER
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