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Re: [TowerTalk] Elevated vertical

To: 'Paul Christensen' <>, "" <>
Subject: Re: [TowerTalk] Elevated vertical
From: Al Kozakiewicz <>
Date: Sat, 24 Dec 2011 00:08:28 -0500
List-post: <">>
Maybe a nit, or maybe not, but transmission line VSWR is determined solely by 
the ratio of the characteristic impedence of the feedline to the antenna 
feedpoint impedence.

Adding a matching circuit at the transmitter (tuner) or adjusting the length of 
the feedline such that a 50 ohm resistive impedence is presented to the source 
does not change the VSWR in the feedline.  Yes, the VSWR between the source and 
the tuner will be 1:1, but the VSWR in the feedline will remain unchanged.

At HF with decent coax (or open wire line) we normally don't care too much 
about the absolute number as long as it's a "reasonable" SWR.  Just don't be 
fooled into thinking that just because a tuner does its job that the VSWR on 
the transmission line is 1:1.  It's not.


-----Original Message-----
[] On Behalf Of Paul Christensen
Sent: Friday, December 23, 2011 10:36 PM
Subject: Re: [TowerTalk] Elevated vertical

> "Would you consider my 130' center fed dipole "resonant" on 60 or 30 m 
> because the antenna tuner inside the rig can tune the 
> antenna/twin-lead/balun/coax to a 1:1 SWR inside the rig?  Sorry to say
> but that one hurts my head to think of as "resonant".   Tuned? yes. 
> Matched?  Yes. Resonant?  No."

How are you defining the terms "tuned," and "matched?"  What is tuned and what 
is matched?  How is your use of "tuned" different than "resonant?" 
Your antenna in this example is not resonant at the antenna feed point, but 
resonant as a system attached to a transmission line with the help of the rig's 

Let's consider your example of a 130 ft center-fed dipole with some length of 
transmission line being used on 60 or 30m.  If the tuner in the rig is 
performing it's job and it attains a 1:1 VSWR at the input to the tuner, then 
your 130 ft dipole and transmission line are resonated, where the system 
reactance is zero. That's a resonant antenna system - where circuit reactance 
is zero.  In some circles, it's also called "tuned."  See below.

Tuned = Resonant = 0 reactance = X(0).

That's the X value but R may be a value well above or well below 50 ohms, but 
your antenna is still resonant.  However, is it also matched at the line input 

I just assisted in the design and installation of a 160m "T" radiator 
consisting of 85' ft of vertical section and a 130 ft. flat top section. 
Using 4Nec2 software, the feed-point Z was close to 50+j200.  This value was 
confirmed with a Vector Network Analyzer.  Under this condition, tuning the 
antenna to resonance and matching the antenna to 50 ohms resistive requires a 
low-pass L network, or simply a series capacitor to cancel inductive reactance 
by an equal but opposite amount of capacitive reactance.  In this case, one 
series capacitor will tune the system to resonance, while ensuring that the 
input remains matched at 50 ohms resistive (50+j0) for a 1:1 VSWR. 
It may have also been possible to achieve the same result by changing the 
feedline length to also tune the system into resonance.  But tuning to 
resonance may not have yielded an R=50 value.

Through the decades, this topic has been presented over and over again by QST's 
editors with re-prints of By Goodman's classic article: "My Feedline Tunes My 
Antenna."  Here, Goodman used the term "tune" to denote resonance. 
Rather than using line length to resonate the system as discussed by Goodman, 
the tuner in your rig is doing it for you, and it's performing the full tune 
(resonating) and match function to attain 50+j0 at the tuner input for a 1:1 

Paul, W9AC 


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