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Re: [TowerTalk] Elevated vertical

To: Towertalk <>
Subject: Re: [TowerTalk] Elevated vertical
From: Ken <>
Date: Sat, 24 Dec 2011 11:15:43 -0500
List-post: <">>

I think you forgot to differentiate between the actual SWR and what a meter may 
read  ;-)

Just because a meter says the SWR is 5:1, doesn't necessarily mean it is so.  A 
meter at different points may indicate a different SWR, but that may not be the 
actual circumstance.   

Besides, where did you get an SWR meter for a 600 ohm balanced line?   ;-)    
Inquiring minds want to know!  LOL

My Christmas wish for all:  May Santa bring you an 80 m open wire fed dipole on 
a pair of 60' towers with plenty of open wire line, and a quality balanced 
auto-tuner and then we can end these discussions!  LOL.  (j/k)    Yeah, I know, 
for the real hams, it has to be a rotatable dipole on a 90' tower.  

73 es Merry Christmas to all,


On Dec 24, 2011, at 10:38 AM, Paul Christensen wrote:
> Sometimes VSWR does change significantly along a line -- and not always for 
> reasons of loss nor common-mode RF current on the outside of a coaxial line. 
> Consider this example:
> At the operating frequency, a dipole at its input terminals is exactly 50 
> ohms resistive (50+j0).  Let's feed the dipole with an electrical half-wave 
> of low-loss 600-ohm open line. VSWR on the line is 12:1.  Correct? 
> Finally, let's connect a random length of 50 ohm, low-loss coax to the input 
> of the 600 ohm line.
> What is the VSWR on the 50 ohm section of line?
> Possible Answers:
> A. Is it still about 12:1 because VSWR does not change on a low-loss line.
> B. Not enough information because you didn't state the coax length.
> C  It's now about 6:1
> D. It is now 1:1
> E. You can't terminate a coaxial line into a 600-ohm balanced line without a 
> current balun and get an answer.
> F. None of the above.
> Bonus question:  What is the impedance at the input to the 600-ohm line 
> section?
> So, here we have one transmission line composed of two types.  Ignoring 
> loss, is the VSWR really the same at all points on the transmission line?
> Paul, W9AC
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