[time-nuts] "Q for dummies"

[Mike Feher]

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