Towertalk
[Top] [All Lists]

## Re: [TowerTalk] Elevated vertical

 To: towertalk@contesting.com Re: [TowerTalk] Elevated vertical Jim Lux Sat, 24 Dec 2011 08:09:31 -0800 mailto:towertalk@contesting.com>
 ```On 12/23/11 7:36 PM, Paul Christensen wrote: >> "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?" > 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). This is the classical resonance condition for a resonant system (e.g. mass on a spring, single RLC). Where we get wrapped around the axle is when we try and use a RLC conceptual model for an antenna. Antennas look like a RLC only over a narrow range, and it's not a particularly good model either (a classic resonant circuit will be symmetric in squared frequency, antennas, in general, are not) > > 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)? "match" is even more ambiguous, especially when talking about a source which may not have a "resistive" or "constant" output impedance. Does it mean that the impedance happens to be equal to that of the transmission line? Or that maximum power is transferred to the load from the source? Or that we are making most efficient use of the power supplied to the system (so transmitter efficiency gets in the game) We like to think in terms of all devices having 50 ohm resistive Z, so hooking up 50 ohm line to a 50 ohm source and a 50 ohm load makes things "matched" in both senses. However, consider a source that has zero output impedance. Maximum power is probably transferred at a load impedance other than 50 ohms, even if there is 50 ohm line. > > 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. _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread Re: [TowerTalk] Elevated vertical, (continued) Re: [TowerTalk] Elevated vertical, Paul Christensen Re: [TowerTalk] Elevated vertical, Paul Christensen Re: [TowerTalk] Elevated vertical, Al Kozakiewicz Re: [TowerTalk] Elevated vertical, K8RI Re: [TowerTalk] Elevated vertical, Al Kozakiewicz Re: [TowerTalk] Elevated vertical, Hank Garretson Re: [TowerTalk] Elevated vertical, Paul Christensen Re: [TowerTalk] Elevated vertical, Ken Re: [TowerTalk] Elevated vertical, Paul Christensen Re: [TowerTalk] Elevated vertical, Al Kozakiewicz Re: [TowerTalk] Elevated vertical, Jim Lux <= Re: [TowerTalk] Elevated vertical, john Re: [TowerTalk] Elevated vertical, TexasRF Re: [TowerTalk] Elevated vertical, Mike Ryan Re: [TowerTalk] Elevated vertical, Tom Osborne Re: [TowerTalk] Elevated vertical, john Re: [TowerTalk] Elevated vertical, Jim Brown Re: [TowerTalk] Elevated vertical, K8RI Re: [TowerTalk] Elevated vertical, Paul Christensen Re: [TowerTalk] Elevated Vertical, Terry G. Glagowski Re: [TowerTalk] Elevated Vertical, EZ Rhino