The definition of electrical resonance is when the circuit reactance is
zero. An antenna has zero reactance and is only resistive at it's resonant
frequency. A perfect dummy load has no reactance on any frequency and is
resonant on all frequencies. Resonance has absolutely nothing to do with
the ability of an electrical circuit (antennas and dummy loads are both
electrical circuits) to radiate electromagnetic energy.
73,
Clay W7CE
----- Original Message -----
From: "Jeff Carter" <towertalk@hidden-valley.com>
To: <towertalk@contesting.com>
Sent: Friday, August 07, 2009 12:52 PM
Subject: Re: [TowerTalk] Resonance is over rated
>I respectfully submit that none of that makes any sense in the context
> of a dummy load.
>
> A dummy load isn't resonant, it's resistive. It's a big ol' resistor
> mounted in some sort of heat-dispersing set up. When the other poster
> said he read 55 + j0 he wasn't kidding: The zero part of that means
> that it's a resistive measurement. A negative j (or i, if you're a
> math major) means the system is more capacitive, a plus j is more
> inductive. A zero means it's neither from a practical point of view.
>
> Or so they told us in college.
>
> Jeff/KD4RBG
>
> ---- Original message ----
>>Date: Fri, 7 Aug 2009 14:17:47 -0500
>>From: "Perry - K4PWO" <k4pwo@comcast.net>
>>Subject: Re: [TowerTalk] Resonance is over rated
>>To: "Scott McClements" <kc2pih@gmail.com>,<towertalk@contesting.com>
>>
>>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
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