[TowerTalk] Ladder Line and Coax

Tue, 21 Aug 2001 00:16:24 EDT

In a message dated 8/20/01 6:06:46 PM Pacific Daylight Time, 2@vc.net writes:

<< 
 >
 >Have been thinking of installing a simple antenna to
 >cover the SE in contests and as a backup in general. 
 >Was considering a inverted vee hung from the tower and
 >fed with ladder line & tuner.  I want to cover only 10
 >thru 40.  My question is this: my tower is about 100
 >ft ftom the house and want to feed this antenna with
 >ladder line near the ground, how do I handle that
 >transition to coax? 

 An efficient way to ground-feed a 1 or more halfwave inverted V is with a 
 remote controlled L-network.  Fair Radio Sales sells a Collins c. 30uH DC 
 motor driven variable-inductor that wurks well for such applications.  I 
 used one in conjunction with a PM-DC gear-motor driven Johnson 
 air-variable cap.  This type of antenna is the "Hertz".  It works well on 
 other band where the antenna is multiple halfwaves. Feed-Z at resonance 
 is 2000-ohms, depending on wire diameter.  (Larger diameter wire lowers 
 the resonance Z.)    Thus, a fairly simple ground connection will work to 
 perfection.  However, ground rods do not make the lowest-R HF ground.    
 U.S. Army anti-tank mine research found that HF-RF typically disappears 
 inches below ground.  So ground rods do a better job when they are buried 
 horizontally just under the surface.

 Cheers, Gale.

 > A 4:1 balun, a 9:1 balun, other? 
 >Is it even worth doing with the losses incurred due to
 >the mismatch in 100 ft of coax?  Maybe a trap dipole
 >or inverted vee would be more appropriate?  I just
 >wondered if anyone had tried something similiar and
 >how it all worked out.
 >
 >73, Stew  K3ND
 > >>
You are right about copper rods do better burried horizontal a few inches 
below the ground.  That being the case why not just bury wide copper sheet a 
few inches below the ground?  The area is several times larger.  k7gco

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