Well, I once had a nutty idea which was to detect earthquakes by looking for the phase variation of DTV station pilot carriers due to seismic waves propagating around, thereby changing the physical distance between transmitter and receiver in a cyclic manner until the 'quake calmed down. Doing so would require that the phase stability of both transmitter and receiver, expressed as length units, be within a fairly small fraction of an inch.
I've since figured out that even with a Rb at both ends, this would not work out- something more like an H-maser would be required. And one other thing- I had completely forgotten about Doppler-shifted reflections off aircraft, which often fall right in the frequency range of seismic waves and persist for durations similar to those of earthquakes. But that's what got me interested in time-nuttery. I still intend to do the experiment, just to see what I can learn about what other factors might exist which cause propagation phase variations. Dana On Mon, May 27, 2019 at 11:27 AM Bob Albert via time-nuts < time-nuts@lists.febo.com> wrote: > Well I have enjoyed time and frequency measurement for many years. I > have no equipment (nor do I expect to get any) that can tell the difference > between the current second and the proposed standard. And at one point I > asked if there was a limit on the smallest time interval that could be > discerned. > I do remember being impressed with the Collins gear in the 1950s, and > wanting one of those 7 foot racks of time standards made by General Radio, > the one with the big clock on top. > As the years passed I obtained more and more accurate frequency > measurement equipment, including a home made heterodyne frequency meter > that outdid the Collins radios. Then the lousy radio propagation ended my > dependence on WWV and I luckily obtained a rubidium oscillator. > But that's about as far as I want to go. My HP 8657B resolves 1 Hz at > more than 2 GHz and it can be set to within a very small error with respect > to the rubidium standard. At this point I see no reason to improve my time > and frequency measurement accuracy. > Of course it can be an end in itself, hence the name Time Nuts. So I > propose the question, how many out there have interest in this topic for > academic and psychological reasons, and how many actually have a concrete > reason to be this precise? One part per billion isn't a lot. And some > systems require iron clad synchronism such as space exploration and long > range communication. But the average tinkerer probably doesn't need it. > Bob > On Monday, May 27, 2019, 3:20:24 AM PDT, Dave B via time-nuts < > time-nuts@lists.febo.com> wrote: > > Hi. > > This from the recent ShortWave Radiogram broadcast, may be of interest. > > ~ ~ ~ > > (Snipped stuff about other SI units undergoing a revamp...) > > Scientists now have their sights set on updating the unit of > time: the second. > > Currently, the second is defined by atomic clocks made of cesium > atoms. Those atoms absorb a certain frequency of light. The > wiggling of the light's electromagnetic waves functions like the > pendulum on a grandfather clock, rhythmically keeping time. One > second is defined as 9,192,631,770 oscillations of the light. > > But a new generation of atomic clocks, known as optical atomic > clocks, outdo the cesium clocks. "Their performance is a lot > better than what currently defines the second," says physicist > Andrew Ludlow of the National Institute of Standards and > Technology in Boulder, Colo. Because those optical atomic clocks > operate at a higher frequency, their "ticks" are more closely > spaced, making them about 100 times more precise than cesium > clocks. > > Ideally, the length of a second should be defined using the most > precise timepieces available. A switch might happen in the late > 2020s, Ludlow says. > > The change to the kilogram's definition was carefully > orchestrated so that it wouldn't affect normal people: A kilogram > of flour still makes the same number of biscuits. Any change to > the second will be similarly coordinated. > > So, sorry, there'll be no chance to squeeze any extra seconds > into a day. > > > https://www.sciencenews.org/article/kilogram-just-got-revamp-unit-time-might-be-next > > ~ ~ ~ > > So, perhaps a host of surplus cesium clocks on the market at some point? > > 73 > > Dave B G0WBX. > > -- > Created on and sent from a Unix like PC running and using free and open > source software: > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
