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Re: [TenTec] OT SWR VS Power Loss

To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Subject: Re: [TenTec] OT SWR VS Power Loss
From: "Gary Hoffman" <ghoffman@spacetech.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Mon, 7 Jul 2008 19:01:24 -0400
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
True....you have a resonant circuit.  Not a resonant antenna.

----- Original Message ----- 
From: "Jim Brown K9YC" <k9yc@audiosystemsgroup.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Monday, July 07, 2008 6:12 PM
Subject: Re: [TenTec] OT SWR VS Power Loss

> On Mon, 7 Jul 2008 14:52:10 -0700, Alfred Lorona wrote:
> >Zero reactance in a wire antenna feedpoint is a necessary but not
> >condition for it to be truly resonant. Citing the Antenna Fundamentals,
> >2, page 2-1 of my 16th addition of The ARRL Antenna Book, a resonant wire
> >defined as 'The shortest length of wire that resonates at a given
> >is one just long enough to permit an electrical charge to travel from one
> >end to the other and back in the time of one RF cycle.'
> >Clearly, a short wire with a finite pure resistive radiation impedance is
> >too short physically for the required condition to exist as stated in the
> >Handbook definition..
> >On the other hand, elsewhere in the book, a zero reactance 'resonant'
> >condition does not mention the required physical length of the wire. If
> >is all that is required, ANY wire can be called resonant and there is
> >nothing to distinguish such wires from a halfwave wire. Somehow this
> >sit right with me. What do you think? Do you think that this discrepency
> >begs for a minor clarifying rewrite?
> The text is fine -- you missed an important part of the sentence -- "in
> time of one RF cycle." That establishes the length of the antenna as long
> enough to be resonant. It will only be "very short" if the frequency is
> high! When the antenna is resonant by the definition of the text it will
> resistive.
> It is also possible to resonate a non-resonant antenna by tuning out its
> reactance. Here's a simple example. A quarter wave vertical typically has
> than 30 ohms radiation resistance at resonance, but if we make it longer,
> can find a length where the impedance at the feedpoint is 50 +jxxx ohms.
We can
> then add a capacitor in series to tune out the inductance (+jxxx), and the
> antenna now looks like 50 ohms and matches the coax. Now, we have a
> circuit that includes the antenna and the capacitor.
> 73,
> Jim K9YC
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