OT - Dual Mixer Time Difference instruments

[Joe Gwinn]

War story: I'm involved with some time-obsessed radio amateurs in the design of a Dual Mixer Time Difference instrument, which can measure frequency differences in the parts per trillion and path length differences in the picoseconds. It's a long and arcane story, but the key is the generation of a 1 Hz beatnote and the precise time measurement of its zero crossings. Flicker noise is a big issue. And protecting against 1 Hz leakage is very difficult, as ordinary shielding is almost totally ineffective at so low a frequency. At least it's a 50-ohm system. Anyway, this effort is what led me to the audio opamps made by That Corp and competitors.

Joe Gwinn: Got any more information on your dual mixer thingy?

Are you really sure you want to go there? If you harbor even the slightest bit of perfectionism, even glancing contact can be life changing. Also note that while this is one of the realms in the land orthogonal to real, it has nothing whatsoever to do with music. Anyway, here is a website:

Dual Mixer Time Difference Systems

The three references cited on the webpage will tell the technical story.

[Steve Conner]

Are you really sure you want to go there? If you harbor even the slightest bit of perfectionism, even glancing contact can be life changing.

Nah, I'm an engineer, my definition of perfection is that I got paid and the customer went away happy.

The difference between "meets the spec" and "perfection" has nothing to do with engineering, it's philosophy. Or maybe neurosis. Heck, maybe philosophy and neurosis are the same thing.

I don't do much precision or low-noise stuff, but I have designed temperature controllers for telecom lasers that were stable to better than 10mK.