[time-nuts] "Q for dummies"
Tom Holmes
tholmes at woh.rr.com
Tue Jan 26 20:22:31 UTC 2021
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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