[TowerTalk] Elevated vertical

[Paul Christensen]

Incidentally, the 160m "T" I discussed below was deliberately resonated to 
1.4 MHz -- not to 1.8 MHz.  At 1.4 MHz, Z was 85+j0.  At 1.8 MHz, Z was 
50+j200.  A low-pass L network then transformed that value into 50+j0.

Paul, W9AC

----- Original Message ----- 
From: "Paul Christensen" <w9ac at arrl.net>
To: <towertalk at contesting.com>
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 tuner.
>
> 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 (50+j0)?
>
> 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 VSWR.
>
> http://www.qsl.net/4z4tl/pub/Feeder_tunes.pdf
>
> Paul, W9AC
>
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