Re: [time-nuts] "Q for dummies"
MRI machines use superconducting coils to generate a 1T magnetic field over a volume sufficient for a human body Andy www.g4jnt.com On Tue, 26 Jan 2021 at 21:47, Tom Holmes wrote: > I was told that one of the killers of superconductivity is magnetic > fields. I guess they 'fixed' that. > > Tom Holmes, N8ZM > > -Original Message- > From: time-nuts On Behalf Of Mike Feher > Sent: Tuesday, January 26, 2021 1:07 PM > To: 'Discussion of precise time and frequency measurement' < > time-nuts@lists.febo.com> > Subject: Re: [time-nuts] "Q for dummies" > > I recall back in the late 60’s visiting some friends at BNL. One of them > took me through the cryogenic lab. In one they had an LC running at near 0 > and it could be heard in a receiver. We know for L, Q in its simplest form > is Xl/R. At superconductor temperatures R approaches 0 and therefore Q > approaches infinity. Consequently the circuit oscillated by itself. I was > amazed. Slightly different, but in the same lab they showed me an > electromagnet in a superconductor cooled environment. I noticed it was > wound with uninsulated wire. I inquired about that and was told that > contact resistance is so much higher than the superconductor resistance, > and they could get more turns without insulation. Regards – Mike > > > > Mike B. Feher, N4FS > > 89 Arnold Blvd. > > Howell NJ 07731 > > 848-245-9115 > > > > -Original Message- > From: time-nuts On Behalf Of Dana > Whitlow > Sent: Tuesday, January 26, 2021 9:36 AM > To: Discussion of precise time and frequency measurement < > time-nuts@lists.febo.com> > Subject: Re: [time-nuts] "Q for dummies" > > > > If anybody can even approach doing justice to the Q concept, including why > it matters, in just two sentences, that person will have definitely earned > the "Qulitzer prize" in technical journalism. > > > > Here's my entry: > > > > "A circuit's Q is closely related to its internal energy losses compared > to external energy exchanges. A high Q can mean better efficiency, better > conformance with expected performance (especially in filter applications), > longer ringdown times (wineglass compared to milk glass) and > (unfortunately) higher price." > > > > Dana > > > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] "Q for dummies"
I was told that one of the killers of superconductivity is magnetic fields. I guess they 'fixed' that. Tom Holmes, N8ZM -Original Message- From: time-nuts On Behalf Of Mike Feher Sent: Tuesday, January 26, 2021 1:07 PM To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] "Q for dummies" I recall back in the late 60’s visiting some friends at BNL. One of them took me through the cryogenic lab. In one they had an LC running at near 0 and it could be heard in a receiver. We know for L, Q in its simplest form is Xl/R. At superconductor temperatures R approaches 0 and therefore Q approaches infinity. Consequently the circuit oscillated by itself. I was amazed. Slightly different, but in the same lab they showed me an electromagnet in a superconductor cooled environment. I noticed it was wound with uninsulated wire. I inquired about that and was told that contact resistance is so much higher than the superconductor resistance, and they could get more turns without insulation. Regards – Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 848-245-9115 -Original Message- From: time-nuts On Behalf Of Dana Whitlow Sent: Tuesday, January 26, 2021 9:36 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] "Q for dummies" If anybody can even approach doing justice to the Q concept, including why it matters, in just two sentences, that person will have definitely earned the "Qulitzer prize" in technical journalism. Here's my entry: "A circuit's Q is closely related to its internal energy losses compared to external energy exchanges. A high Q can mean better efficiency, better conformance with expected performance (especially in filter applications), longer ringdown times (wineglass compared to milk glass) and (unfortunately) higher price." Dana ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] "Q for dummies"
Just two sentences is quite a challenge! Maybe one of the two sentences should explain the downsides of a system design that uses filters or networks with high Q. "High-Q filters and matching networks will have circulating currents resulting in poorer efficiency, and higher variation in group and phase delay across the passband and with environmental conditions, when compared to low-Q networks." On Tue, Jan 26, 2021 at 11:52 AM Dana Whitlow wrote: > If anybody can even approach doing justice to the Q concept, including why > it > matters, in just two sentences, that person will have definitely earned the > "Qulitzer prize" in technical journalism. > > Here's my entry: > > "A circuit's Q is closely related to its internal energy losses compared to > external > energy exchanges. A high Q can mean better efficiency, better conformance > with > expected performance (especially in filter applications), longer > ringdown times > (wineglass compared to milk glass) and (unfortunately) higher price." > > Dana > > > On Tue, Jan 26, 2021 at 8:14 AM Lux, Jim wrote: > > > On 1/26/21 5:29 AM, Dave Daniel wrote: > > > That doesn’t really illustrate the fundamental concept of Q. I’ll try > > and think of something that is still non-mathematical but nonetheless > > illustrates the concept of Q. > > > > > > DaveD > > > > Ultimately, Q is about internal (or external) losses (leaving aside > > antennas) - how much energy is stored, vs (how much is radiated) or lost > > to heat > > > > A big heavy pendulum will swing for a lot longer than a light one, > > because more energy is stored in the system, relative to the amount lost > > to air and mechanical friction. > > > > And that, like the wine glass (which is a nice mechanical analogy - the > > fine crystal has less internal damping) is a "impulse response" system, > > not a "driven system" > > > > > > > > But how that relates to bandwidth is a bit tricky, because then you need > > to get into a discussion "driven systems" and then into resonance - and > > that is where the train will come off the rails, particularly with > > respect to antennas. > > > > > > > > > > >> On Jan 26, 2021, at 07:28, Ole Petter Ronningen < > opronnin...@gmail.com> > > 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 > > >> ___ > > >> time-nuts mailing list -- time-nuts@lists.febo.com > > >> To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > >> and follow the instructions there. > > > ___ > > > time-nuts mailing list -- time-nuts@lists.febo.com > > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > > and follow the instructions there. > > > > > > > > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] "Q for dummies"
I recall back in the late 60’s visiting some friends at BNL. One of them took me through the cryogenic lab. In one they had an LC running at near 0 and it could be heard in a receiver. We know for L, Q in its simplest form is Xl/R. At superconductor temperatures R approaches 0 and therefore Q approaches infinity. Consequently the circuit oscillated by itself. I was amazed. Slightly different, but in the same lab they showed me an electromagnet in a superconductor cooled environment. I noticed it was wound with uninsulated wire. I inquired about that and was told that contact resistance is so much higher than the superconductor resistance, and they could get more turns without insulation. Regards – Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell NJ 07731 848-245-9115 -Original Message- From: time-nuts On Behalf Of Dana Whitlow Sent: Tuesday, January 26, 2021 9:36 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] "Q for dummies" If anybody can even approach doing justice to the Q concept, including why it matters, in just two sentences, that person will have definitely earned the "Qulitzer prize" in technical journalism. Here's my entry: "A circuit's Q is closely related to its internal energy losses compared to external energy exchanges. A high Q can mean better efficiency, better conformance with expected performance (especially in filter applications), longer ringdown times (wineglass compared to milk glass) and (unfortunately) higher price." Dana ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] "Q for dummies"
So also, a "bad" Q story may resonate with the audience to reinforce the concepts. There are events like buildings and bridges resonating and collapsing. Ed ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] "Q for dummies"
But Dana, a high Q can also be a bad thing - depends on the situation. Ed ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] "Q for dummies"
If you have a mechanical tuning fork handy, just ding it and note the gradual decay. Then wrap a small wad of paper towel on one or both arms, with some tape outside (not touching the arms - don't want adhesive residue left on there) to keep in place, and repeat. For using a wine glass or such, stuff some paper toweling inside for loss. The point is to use the same resonator for all examples, and represent the loss with something added. Oops - after I wrote this I looked back at the OP and see that it may not be for a live presentation, so no props. If so, the audience may be encouraged to try it themselves with the wine glass analogy - easy to do. Ed ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] "Q for dummies"
If anybody can even approach doing justice to the Q concept, including why it matters, in just two sentences, that person will have definitely earned the "Qulitzer prize" in technical journalism. Here's my entry: "A circuit's Q is closely related to its internal energy losses compared to external energy exchanges. A high Q can mean better efficiency, better conformance with expected performance (especially in filter applications), longer ringdown times (wineglass compared to milk glass) and (unfortunately) higher price." Dana On Tue, Jan 26, 2021 at 8:14 AM Lux, Jim wrote: > On 1/26/21 5:29 AM, Dave Daniel wrote: > > That doesn’t really illustrate the fundamental concept of Q. I’ll try > and think of something that is still non-mathematical but nonetheless > illustrates the concept of Q. > > > > DaveD > > Ultimately, Q is about internal (or external) losses (leaving aside > antennas) - how much energy is stored, vs (how much is radiated) or lost > to heat > > A big heavy pendulum will swing for a lot longer than a light one, > because more energy is stored in the system, relative to the amount lost > to air and mechanical friction. > > And that, like the wine glass (which is a nice mechanical analogy - the > fine crystal has less internal damping) is a "impulse response" system, > not a "driven system" > > > > But how that relates to bandwidth is a bit tricky, because then you need > to get into a discussion "driven systems" and then into resonance - and > that is where the train will come off the rails, particularly with > respect to antennas. > > > > > >> On Jan 26, 2021, at 07:28, 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 > >> ___ > >> time-nuts mailing list -- time-nuts@lists.febo.com > >> To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >> and follow the instructions there. > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] "Q for dummies"
On 1/26/21 5:29 AM, Dave Daniel wrote: That doesn’t really illustrate the fundamental concept of Q. I’ll try and think of something that is still non-mathematical but nonetheless illustrates the concept of Q. DaveD Ultimately, Q is about internal (or external) losses (leaving aside antennas) - how much energy is stored, vs (how much is radiated) or lost to heat A big heavy pendulum will swing for a lot longer than a light one, because more energy is stored in the system, relative to the amount lost to air and mechanical friction. And that, like the wine glass (which is a nice mechanical analogy - the fine crystal has less internal damping) is a "impulse response" system, not a "driven system" But how that relates to bandwidth is a bit tricky, because then you need to get into a discussion "driven systems" and then into resonance - and that is where the train will come off the rails, particularly with respect to antennas. On Jan 26, 2021, at 07:28, 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 ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] "Q for dummies"
That doesn’t really illustrate the fundamental concept of Q. I’ll try and think of something that is still non-mathematical but nonetheless illustrates the concept of Q. DaveD > On Jan 26, 2021, at 07:28, 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 > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] "Q for dummies"
Ole, For a two-sentence summary, I think the wine glass example of Q works fine. The audience typically knows about bells ringing and wine glasses singing, so this factoid resonates with them. But the issue is then: what's the point; why is a long bright ring better than a short dull plink. That's where it gets hard. For a deeper look, I keep a list of articles about Q here: http://leapsecond.com/pages/Q/ Of those, I would recommend reading at least this one all-time classic note from Bell Labs: http://leapsecond.com/pages/Q/1955-The-Story-of-Q-Green.pdf It's relevant to from quartz and atomic clocks, from wine to earth rotation. /tvb On 1/26/2021 4:28 AM, 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 ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] "Q for dummies"
You could mention it is roughly equivalent to the number of swings you get for a weight on a rope before it stops swinging. Or something like that. Andy www.g4jnt.com On Tue, 26 Jan 2021 at 13:14, 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 > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] "Q for dummies"
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 ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
