[TowerTalk] Resonance is over rated

[Martin Ewing]

These discussions are useful because they bring out some important
concepts (and mis-concepts) around antennas and tuned circuits.

Another way of thinking about dummy loads:  Any practical two-terminal
device has inductive and capacitive reactance along with resistance.
Whether you call it an inductor, capacitor, or resistor depends on
your operating regime and your point of view.

Mathematically, you can think of an ideal resistor as what you have
(in a parallel tuned circuit) in the limit when XsubL goes to zero and
XsubC goes to infinity at a given frequency.  Q = XsubL / R, goes to
zero in that limit.  The resonant frequency, where XsubL = XsubC, is
undefined.

Yes, that's a perverse view and not very practical, except to show
that short leads and good lead dress make for better dummy loads.
There are many ways to skin a cat.

73 Martin AA6E

On Fri, Aug 7, 2009 at 3:17 PM, Perry - K4PWO<k4pwo at comcast.net> wrote:
> Resonance, in the normal sense has nothing to do with the value of impedance
> only in a minimum (for a series tuned configuration) or maximum (parallel
> tuned).  While its possible to make the argument that a dummy load is a
> resonant "antenna" with a Q of 1 (Q=Fr/BW or infinity/infinity) the concept
> of a "resonant frequency" of infinity is counter intuitive.  Since "dummy
> loads" are made with real world components, we know that the "resonant
> frequency" can not be infinity.  So in that sense, the "dummy load" is a
> very low, non unity Q "resonant circuit" but it fails in fitting a second
> order differential equation for circuit analysis.  If the shoe doesn't
> fit...
> That still doesn't negate the fact that radiation efficiency is the key to
> propagating a signal.
> BTW, I operate a fairly effective "dummy load" on HF... a B&W BWD-180
> terminated folded dipole.  It's pretty flat from 1.8 to 30 MHz. but its
> efficiency is all over the place in that range.
> It works but...
>
> 73 de Perry - K4PWO
>
>
> ----- Original Message -----
> From: "Scott McClements" <kc2pih at gmail.com>
> To: <towertalk at contesting.com>
> Sent: Friday, August 07, 2009 10:57 AM
> Subject: Re: [TowerTalk] Resonance is over rated
>
>
> How do you define resonance?  My dummyload on 80 meters shows an
> impedance  of 55 + j0 Ohms, it doesn't get anymore resonant than that.
>
> -Scott, WU2X
>
> On Fri, Aug 7, 2009 at 3:37 AM, Perry - K4PWO<k4pwo at comcast.net> wrote:
>> The dummy load isn't resonant
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