Q is a matter of definition. The first definition kids usually learn is X/R. Resonators have a Q by the same definition (given a suitable equivalent circuit, like a series RLC), understood to be measured at the resonant frequency (w = 1/sqrt(LC)), unless specified otherwise in which case the first definition is probably used.
You can go further and talk about the Q factor of a resonator in a system; this might be very low, such that a filter with high bandwidth is made. In that case, you want the resonator or component Q to be much higher than the system Q, so as to get good efficiency (low insertion loss).
I've seen (1 + Q^2) terms pop up in equations, frequently enough that it seems worthy of a symbol. In that case, you might take the liberty of using a suitably marked variant, maybe a Q', or K (for koalaty factor, if you're Aussie ;) ) or something.
Or you can take the Q factor of a power system, like with generating or rotating machinery. The Q factor of the power grid is usually very low, 0.1 or thereabouts -- there's not that much stored or reactive power in all the high voltage transmission lines, PFC caps, line reactors and rotating machinery.
The only problem in power, is, well, power: they use S = P + jQ for apparent, real and reactive power, respectively. So you have the potential confusion that Q(quality) = Q(reactive) / P... :-)
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: https://www.seventransistorlabs.com/
"Tom Del Rosso" wrote in
message news:phrcj5$mum$1@dont-email.me...
> John Larkin wrote:
>>
>> My next task is to wind a coil and measure its Q, and measure my
>> existing Coilcraft parts for comparison. At a pulse rate of, say, 4
>> MHz, I need to know the Q at the fundamental and significant
>> harmonics, so I can look at the FFT of the current waveform and
>> trediously compute total power dissipation. I also need to evaluate
>> the effects of PCB planes on inductor Q.
>>
>> I'm thinking that I'll be seeing Qs from roughly 50 to 500.
>
> As I understand Q it applies to a tank, so how can the inductor by itself
> have a Q factor?
>
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