[TowerTalk] resonance/swr/impedance plots

[Guy Olinger, K2AV]

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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