[TowerTalk] End Fed W8JK

[K7GCO@aol.com]

I don't know where the 8jk would be on the Internet.  It is real simple.  Run 
parallel 1/2 waves 1/8 WL apart.  Bend the ends (one end only) in to a 
450--600 ohm open wire line 68 or 136' long (.98 VF) and use a Johnson Match 
Box--with my modifications.  End feeding does a great job and is more 
efficient than center feeding.  When center fed so that the dipoles are 180 
degrees out of phase, the close and critical coupling and the 180 degree 
phasing results in maximum gain both ways of 4 dB with a real tight figure 8 
pattern.  It used open wire line between the elements twisted 180 degrees and 
the feedline is connected to the center of the phasing line.  See the ARRL 
Antenna books of the last century of about 60 years ago.  I still see them at 
the flea markets.  The Z was very low and hard to feed.  End feeding has very 
high voltages but should be manageable.  My magic feed line length will have 
the same high voltages and Z at the end of the feedline as is at the antenna. 
 If matching it is a problem, add a shorted 1/4 wave and tap on to this stub 
at a point where a 600 ohm Z is around 1/3rd up from the shorted end.  Create 
your own impedance for the feedline.  You can use a version of the "Twin Bulb 
SWR Indicator" many used in the last century to check SWR on open wire line.  
One can parallel the terminals on RF ammeters on one leg of open wire line 
and measure the relative current along the line without cutting it.  When you 
can attach the RF ammeter anywhere on the line with no or little current 
reading change, your SWR is very low and it called a flat line.  This is 
ideal for determining the 600 ohm tap on the shorted 1/4 WL line. Ham Radio 
had an article on the 8JK used on different bands with the same length and 
spacing.  When and if I ever get time I will do an article on it as I plan to 
use it extensively vertically, horizontally and at 45 degrees.  John Kraus of 
Ohio State W8JK who is still alive came up with this antenna in the 30's.  
K7GCO

In a message dated 6/19/00 12:11:46 PM Pacific Daylight Time, 
eDoc@netzero.net writes:

<< Where might one find this antenna design detailed on the
 Internet?
 
 Has anyone run complete EZNEC or other analyses on
 it?
 
 - Thanks! & 73, DavidC  K1YP in Hudson, FL
 
 ************************************************************************
 >  The end fed vertical 8JK is a simple and very effective antenna.
 >  I had one for 40 meters hung from a tree years ago.  The ends
 >  were brought together and voltage fed directly with a balanced
 >  antenna tuner.  The voltages are very high and safety precautions
 >  are necessary.
 >
 >  This antenna provided my first ever JA contacts from the east
 >  coast with low power.
 >   >>
 >
 > The 8JK is a great antenna horizontally or vertically polarized with 4 dB
 > each way in a tight figure 8 pattern.  You can hear your CW signal coming
 > around the long way when the band is really open due to gain both ways.
 It
 > is 1/16th WL shorter also.  When vertically polarized no radials are
 needed
 > either.   Or run it at 30-45 degrees off the tower using a wood T-Bar.
 k7gco
 
  >>

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