[time-nuts] Strange oscillations
John Ackermann N8UR
jra at febo.com
Sat Sep 4 20:03:54 EDT 2004
Jeffrey Pawlan wrote:
> The very first attempt I made at designing a precision frequency
> standard myself, I found out that it is true that the orientation of the crystal
> relative to gravity is VERY significant. I was working at that time in a
> company that owned a labratory rubidium standard. I compared my 10MHz output
> against the Rb simply using an oscilloscope and looking at the resulting
> lissajous pattern. I was shocked to see the phase move and even rotate
> beyond 1Hz difference with the orientation of my oscillator. I was using a
> crystal made by International Crystal, AT cut, and made as high a precision as
> they could supply.
There's a really excellent book called "Tuxedo Park" about Alfred Loomis, Wall Street multimillionaire and amateur physicist extraordinare of the 1920s through WWII.
He was seriously into time measurement and in the '20s bought 3 of the Shortt pendulum clocks, at that time the most accurate clocks in the world. He mounted them on rock pedestals in the basement of his mansion/laboratory and even with those "crude" devices was able to see the effect that the pendulum of one clock had on the others. He ended up having to orient the three clocks with the pendulums swinging 120 degrees relative to each other to minimize the effect.
Other Loomis time anecdotes -- he had a dedicated phone line to Bell Labs which sent a 1000 cycle note from their crystal standard to his lab; he and the Labs guys would compare notes. He would routinely write to the standard frequency stations around the world to tell them how far off they were (remember, this was just as crystals were coming into use, so propagation was swallowed by the equipment errors. And, in his older days, he used to wear two Accutron watches, one on each wrist, and reverse them regularly to correct for left vs. right orientations!
Great book, well worth a read.
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