[TowerTalk] Open Feedlines

[K7GCO@aol.com]

 In a message dated 8/28/01 9:43:14 AM Pacific Daylight Time, 2@vc.net 
writes: << 
  >
  >Guys,
    >Reviewing the wireman's "Loss Graph for Matched Transmission Lines" 
chart,
  >and I noticed #12AWG Twin Open Wire, as having the lowest loss by a long
  >way.  I guess I have never seen Open Wire as shown on a chart before to
  >reinforce just how low the loss really is.
  >Being a novice antenna guru, I have a few questions:
  >
  >How far away from the ground does this stuff need to be?
  
  //   My guess is that it should be >5-times the wire-spacing.   
  
  >What are the drawbacks of using it?
  >
  It won't work as advertised when fed from an unbalanced tuner with a 1 to 
  1 balun at the output.  However, a Balanced L-network antenna tuner is 
  not hard to construct.  An article was published in the February, 1990 
  *QST*.  The manuscript for the balanced tuner article is available on my 
  Web site.    
  
  >I have a remote dipole that this stuff might be just the ticket for a long
  >run.  I have always used coax, except for some plastic windowed ladder
  >line, which always worked nicely, but according to the chart has more loss
  >that the Twin Open Wire.
  
  //   Yea, verily. . .  Homebrewed #12-solid-Cu open wire line has low 
  loss - even with over the top SWR, so the antenna it feeds works for 
  multiband use.  However, open wire feedline needs to be guyed with 2 
  Dacron cords to keep it from flailing around in strong winds.  
  >
  >My guess is that this is the 6" spaced feedline I have seen before.  I
  >would make this and wonder what people use for the spacers, what spacing is
  >required, etc.
  
  //   The above article also describes a simple way of constructing 
  open-wire feedline using commonly available materials and tools.
  
  good luck, Eric
  
  -  R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.  
  end
   >>
 
 Very good advice Rich. 
 
 Inadditon to the tuners mentioned, the Johnson Match Box does a great job.  
Using my "magic length" of open wire feedline reduce reactance values as it's 
a 1/2 wave or multiple on all bands.  It's 135' and 123' for 450 ohm Ladder 
line.  QST always says "any length" which is just plain stupid and why many 
have problems getting a match by some tuners and/or arcing.
 
 When I grid dip a length of feedline that I use frequently, I short both 
ends and tie both ends to a tree or other support with a rope.  I find that 
at about 4' above ground there is no affect of the ground on the resonant 
frequency.  The closer it is the resonant frequency changes.  Try it and you 
will see.  The resonant frequencies will repeat all the way to 10M real 
close.  I grid dip it when installed also and modify as necessary.  I run it 
through walls and floors with no problem with hollow insulator tubes.  I use 
3.562 MHz as a base frequency if used on 80M.  It will be a 1/2 multiple at 
7.125, 10.688, 14.25, 17.812, 21.375, 24.937, & 28.5 MHz.  Insulators about 
3' apart give about a .98 VF.  The higher the number of insulators the lower 
the VF.  It's measurable.  Well made it will last you a life time. k7gco 

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