[TowerTalk] TH7 SWR trouble ... Coax balun question

K7GCO@aol.com K7GCO@aol.com
Thu, 4 May 2000 15:00:43 EDT

In a message dated 04.05.00 06:53:13 Pacific Daylight Time, 
markku.a.oksanen@nokia.com writes:<< 
 I think I may have left something out:  You may remember that the TH6
 instructions call for a 12-turn balun located at the junction of the boom
 and the mast, couple of feet from the feedpoint with the coax to the
 feedpoint taped to the boom.  OK, I did not do this for the TH7, however I
 do have about 8 inches of taped RG213 on the boom between the 6-turn, single
 layer coil. I am beginning to think that this may be the reason, the taped
 part may contribute a small capacitance to one side of the feedpoint.  Any
 other opinions?  
 How did others use the coax balun with a TH7?  How is it attached?  Length
 of pigtail wires to the antenna feedpoint?  Length of coax between pigtails
 and balun coil?
 Markku OH2RA
There is a balun without toriods in it ideal for your beam in one of Bill 
Orr's Handbooks that works great in the Hi Current area with the least number 
of turns.  It only covers 3 bands and has the least loss of all baluns.  It 
has a bifiler winding it also which is the key.  It's the only coil balun I'd 
use in the Hi current area.  It doesn't even get warm with high SWR either.  
What ever you use, use the 'K7GCO hand test" below the balun on the coax.  If 
the SWR changes, it's not much of a balun.  Use the Palomar RF current meter 
below the balun for a more sensitive test if you want a clean balun.  Be sure 
and lift the coax shield off the boom before the balun.  K7GCO

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