[TenTec] tuners and ladder line

[Sherrill WATKINS]

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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