[TowerTalk] resonance/swr/impedance plots

[n4kg@juno.com]

I think the word RESONANCE is being over-used here.

Antenna resonance occurs when the antenna is 1/2 WL
(or a multiple) and the feed impedance exhibits ONLY
a resistive component (not necessarily 50 ohms).

It is quite feasible to MATCH a non-resonant antenna
to 50 ohms through a tuner.  The system is then 
MATCHED but NOT resonant.

de  Tom  N4KG

On Thu, 30 Nov 2000  "Guy Olinger, K2AV" <k2av@contesting.com> writes:

> A tuner does not make an antenna resonant. It tunes out the reactance
> that's there because the antenna is NOT resonant, and also effects a
> transformation in case the ohmic portion of the antenna's feed 
> impedance is not what you want.
> 
> Back to the original post and your objection. I said that an 
> inverted L wire that was long enough to be 50 +jx  on 160 
> was not resonant, but  a series cap at the feed point would 
> zero the reactance and leave you  a 50
> ohm feed point nicely matching 50 ohm coax, PLUS raising the feed
> impedance to reduce the effects of any ohmic losses in the ground
> connection.
> 
> Consider that capacitor a one-piece antenna tuner. A tuner does not 
> make an antenna resonant, it makes the SYSTEM resonant from the view 
> point of the transceiver or connecting coax.
> 
> Resonance is one of those sloppily used words that also has a very
> specific technical meaning, not all that closely matching the 
> general usage.
> 
> Appearance of resonance = SWR is low.  A lot of conversational usage
> says "my antenna is resonant" whenever the SWR is low at the end of 
> the
> feedline. No one is pulling the whip loose, fastening it to 65' 
> radius
> dense ground screen all by itself and trying to get a 75 meter dip 
> on it
> from a grid dip meter.
> 
> You can make the SYSTEM resonant at 75 meters with coils, taps, etc. 
> But
> the ugly low efficiency and narrow bandwidth will be governed by the
> fact that the whip itself is not anywhere close to resonant on 75
> meters. The whip itself will probably grid dip in the high twenties, 
> or
> maybe even low thirties (MHz).
> 
> --... ...--  . ...  --.  .-..
> 
> Regards, Guy
> Apex, NC
> 
> 
> ----- Original Message -----
> From: <K3BU@aol.com>
> To: <towertalk@contesting.com>
> Sent: Wednesday, November 29, 2000 9:33 PM
> Subject: Re: [TowerTalk] resonance/swr/impedance plots
> 
> 
> > In a message dated 11/29/2000 9:11:24 PM Eastern Standard Time,
> > k2av@contesting.com writes:
> >
> > > A tuned up 10 foot whip on 75 has the APPEARANCE of
> > >  resonance. But it has FEW of the ADVANTAGES of resonance, like
> > >  efficiency and bandwidth.
> >
> > Another huh?
> > Appearance of resonance? (What is that?)
> > Doesn't efficiency have to do with losses and bandwidth with Q of 
> the
> antenna
> > (or tuned circuit)?
> > So the tuned circuit can't be resonant, or tuned circuit with some
> antenna
> > wire attached to it can't be resonant? Appears to be resonant? 
> Like
> half
> > pregnant?
> >
> > Yuri, K3BU/m
> > with "appearancy resonant" whips?
> >
> > --
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> >
> 
> 
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