Carl: Yes; your assessment is correct. Converting from open wire
line to a lossy type balun may defeat the purpose of using a open
wire feeder. However, there is a way around this dilemma.
Use two parallel runs of the largest diameter coaxal cable you can
find. (Use the type of coax with the highest voltage breakdown rating
you can obtain.) Use equal lengths and at each end tie the outside
shields together. You now have made two parallel, shielded
conductors that you can "snake" through a wall, etc. At
a convenient location near the outside of your house, just connect
one of the open wire lines to each one of the center conductors of
the coax. Presto; works great! I have talked to several ham's who
have used this approach and it works like a champ! The two parallel
conductors of coax form a shielded and balanced line. Since the
shields are tied together at each end, the shield will not radiate
because the currents are equal and opposite so they cancel. The
exact nominal impedance of the coax is not important, but try to use
the largest diameter you can for high voltage breakdown protection.
Also, the higher the nominal impedance the better. Two lines of coax operated
this way will have twice the nominal impedance, twice the operating voltage
rating and ½ the loss of a single line! I have
always just located my antenna tuner in front of a window beside the
main rig. I have just replaced the glass window panes with clear
acrylic plastic sheet of the same thickness as the glass pane. Then
I just drilled a hole in plastic sheet the same distance apart as the
open wire line. Then install grommets and just feed the open wire
directly through the window. Use clear silicone calk to seal the
outside window pane from leaks. (If you can drill the glass pane
without breaking it you don't need to replace the glass.) This
works like a champ! I also had aluminum storm window on the
window. So I replaced the large sheet of storm window glass
with acrylic sheet the same thickness and did the same technique.
Worked like a champ! No, the aluminum storm window did not
get hot or radiate rf or anything! I used open wire line with 6"
spacing; but 2" is good enough. Let your amateur good sense
and intuition be your guide. Don't listen to old fogies on 75 meters
that will tell you nothing but a balun and coax will work!! By the
way, if you ever visit the Voice of America's transmitter site at
Greenville, NC, you will see some unbelievably HUGE curtain
(stacked and phased dipole) antennas that are fed with 50 kW
of rf energy! All the transmission lines are either two wire or four wire
open type. Remember, those transmitters change frequency with
he seasons of the year as the propagation changes and feed into
one or several antennas. Should not that tell us something about
open wire line? Warning: If one uses open wire line and feeds
more than several KW through it to a reactive antenna, and if one's pet
cat crawls across the open wire, it may have a serious problem.
-73's- Corn -k4own
Corrupt politicans love unarmed serfs.
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