@Science

So here is a question some of my EE and radio friends disagree on... Is a purely resistive matched load, like a 50 ohm dummy load, considered "resonant". In the strictest sense of the word is that a valid term here?

While it would seem odd I'm leaning towards yes, and would be the simplest example of resonance.

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I'd say matched, but not resonant. You need to have two non-vanishing (usually frequency dependent) complex reactances to cancel each other out.
I lack the imagination to consider a strictly real resistance "resonant".
@freemo @Science

@tatzelbrumm

Your perspective is not uncommon of course. Though from that perspective the "non-vanishing" part isnt true. Any combination of capacitive reactance and inductive admittance, no matter what values are picked, will vanish at their resonant frequence. That is the textbook definition of resonance, the frequency at which the system is purely resistive without measurable reactance. A resistor just happens to satisfy that at all frequencies.

@Science

@freemo @Science
That's just the outside view of a resonator. An actual resonator moves energy back and forth between the reactances at twice the resonant frequency. A pure resistance only dissipates energy, but doesn't store any.

@tatzelbrumm

Well depends on who you ask. That is certainly one perspective you might hear, though not necessarily a universal definition.

Also just to clarify the signal is not twice the resonant frequency. It should complete once back and forth cycle for every cycle of its resonant frequency.

The problem with your definition, rather than the one I gave, is that it excludes most resonant things.. A crystal oscilator is clearly resonant and yet has no reactive components of any kind.

@Science

@freemo
You asked me, a physicist, and as such, I'm giving you the universal definition that does not depend on what other people think.
A crystal oscillator has a lot of energy stored in mechanical vibrations, even though the coupling of that energy to the electric circuit, via the piezoelectric effect, is weak.
As for "twice the resonant frequency":
Shut up and calculate!
(specifically, the energies in the electric field of a capacitor and the magnetic energy as functions of time in an inductor of an undamped LC tank circuit in resonance).
You may then proceed to grab a textbook in Theoretical Mechanics and do all the exercises about pits and pendulums, and the periodic transfer of kinetic to potential energy and back.
@Science

@tatzelbrumm

I asked people to offer their opinions, and i am happy you did so. lol you just told a professional Electrical engineer with an advanced degree that includes RF engineering to pick up a text book on capacitors, really... What a pompus response.

I appreciate your opinion, but I know full well what the cycle in a resonant circuit looks like, and no it does not complete a full round trip at twice the frequency. As i stated it completes one cycle, from capacitor to inductor and back to capacitor once per cycle. The fact that you are disagreeing with this fundamental fact puts your credentials in question if you are really going to hold steadfast to that.

The fact that you are defensive over being corrected, particularly over such a fundamental assertion doesnt really help your image IMO.

@Science

@tatzelbrumm

Just to be clear as I stated earlier I do not disagree with your definition, as i said it is common enough. But there are multiple definitions and no one official definition. so it is very much a matter of interpretation, there is not a single answer.

One could even argue that the definition involving an actual transfer between potential and kinetic energy holds true for a resistor at a molecular level. If i have a red object and shoot EM waves at it that is red then the red object absorbs more energy than if i shoot green EM at it. Because at a molecular level the molecules are resonant to one color and not the other, and thus absorbs one color more than the other. similarly if the object is black it is equally responsive at all frequencies, but the process is no different.

We can see a similar analogue in all resonant systems, whereby the system can be made to resonant to any frequency equally. We call these "universal resonators". In that sense a black body can be thought of as the universal resonator for that example. If we are talking about caviry resonance this has been demonstrated with air cavities as well where the Helmholtz resonance is universal. In my mind a resistor is really no different, it is simply the universal resonator in an electrical system (though again i agree it is unusual to refer to it as such technically speaking it is valid).

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