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## Re: [TowerTalk] Elevated vertical

 To: Re: [TowerTalk] Elevated vertical "Paul Christensen" Fri, 23 Dec 2011 22:50:33 -0500 mailto:towertalk@contesting.com>
 ```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" To: 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 > > _______________________________________________ > > > > _______________________________________________ > TowerTalk mailing list > TowerTalk@contesting.com > http://lists.contesting.com/mailman/listinfo/towertalk _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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