[time-nuts] "Q for dummies"

[Magnus Danielson]

Hi Ole,

I think you already got plenty of good answers. I just want to highlight
a few of the things I end up trying to stress when I have to explain the
same thing.

As you have resonance, the amplitude decreases because of loss, and
classically this quality factor is denoted Q. With lower loss, the
amplitude reduction will be less for each cycle, such that the next peak
will be 1/Q less than the previous one. Thus, a higher Q denotes a
higher quality in that it has less loss.

The width of the resonance (delta f), when viewed as amplitude response
vs frequency, will be the center frequency f divided by Q. Thus, higher
quality gives narrower filter, as this was historically the property
which one attempted to achieve.

While being a someone theoretical relation, for some it is useful to
explain and help to remember basic relationship, at the same time it
coveys some simple mental models. Exactly how one explains it depends on
what people are good at.

Cheers,
Magnus

On 2021-01-26 13:28, Ole Petter Ronningen wrote:
> Hi, All
>
> I am going to give a presentation to non-nuts, and in one of the slides I
> touch on Q - not wanting to spend more than a sentence or two on the
> subject, I wonder if the following analogy works:
>
> "A quality long-stemmed, thin-walled wine glass will ring for a long time
> after we give it a little tap - this is high Q. A thick-walled, stubby milk
> glass will barely ring at all, just a dull "plink" - this is low Q. The
> energy we put in dies out very quickly."
>
> As I am sure is embarrassingly evident, I have a rather tentative grip on
> the subject myself..
>
> Ole
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