[TowerTalk] Change in SWR

[Mike & Becca Krzystyniak]

Hi Doug,

   I agree that Rick's proposal is probably the quickest way to determine
interaction.  Some many years past, we used to use this method to tune
parasitic elements on wire arrays by applying shorts, opens, and reactive
loads (bread slicer caps or inductors), to the coax there in the shack.
Today, a classic antenna tuner would work quite well to give you a wide
range of terminations that could be used to reflect that up to the parasitic
element feed, or in this case your wire antenna.

    You could also put an SWR bridge there in line with the wire antenna and
look at how much power is coupling to the wire and coming back into the
shack.  I dare not speculate the interaction to the array factor but it will
give you a clue as to what is talking to what, and there is probably a
termination that you could hang on the wire antenna feed line there in the
shack that would minimize the coupled effects.  Unfortunately it is
difficult to predict if this has a first order effect on your change in SWR,
or something else is dominant.  YMMV.   Good luck with it.

Mike K9MK
   


-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Rick
Stealey
Sent: Wednesday, December 04, 2013 8:58 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Change in SWR

Doug, 
I'd like to suggest something to try.  I haven't actually done this but it
might bring results, and won't cost you a dime, or even get your feet or
fingers cold, no matter how cold it is at your QTH.

Your low dipole, MAY be coupling to the yagi, that's the concern, right?
And if so, if you detune it, the amount of interference would change.  So my
idea is to NOT go out to the antenna feedpoint and do anything but rather to
put variable impedance across the feedpoint of the low dipole in the shack.
Use an antenna tuner, and tune it through every impedance you can, all the
way from a short to an open and everything in between.  These impedances
will be transformed to some other impedance at the feedpoint of course.  The
objective is just to see if ANY impedance will cause any change in SWR.  If
you see any effect whatsoever you know there is some amount of coupling and
you can take it from there.  But right now I believe your concern is whether
the new dipole is involved in the SWR changes, and this technique should
answer that question for you.

Rick  K2XT


 		 	   		  
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