[time-nuts] "Q for dummies"

[Andy Talbot]

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 <tholmes at woh.rr.com> 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 <time-nuts-bounces at lists.febo.com> On Behalf Of Mike Feher
> Sent: Tuesday, January 26, 2021 1:07 PM
> To: 'Discussion of precise time and frequency measurement' <
> time-nuts at 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 <time-nuts-bounces at lists.febo.com> On Behalf Of Dana
> Whitlow
> Sent: Tuesday, January 26, 2021 9:36 AM
> To: Discussion of precise time and frequency measurement <
> time-nuts at 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
>
>
>
>
>
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