Is that really how it's done ?
I was watching this Veritasium video on Ytterbium based atomic clocks (OMG a rare earth element !).
These clocks are precise enough to allow at least an order of magnitude better measurement of the Einstein prediction of how gravity changes space-time.
source: https://www.youtube.com/watch?v=eyZEqSPeMwg
the NIST blog page on this experiment: https://www.nist.gov/blogs/taking-measure/putting-einstein-test-worlds-most-accurate-clocks
The original clock based tests (Hafele and Keating in 1971) were done with Cesium based clocks - those clocks have a signal with a frequency of 9,192,631,770 Hz or 9.1 GHz. Curiousmarc on Youtube has recently been refurbishing similar equipment to attempt to duplicate the initial experiments, the latest was fixing a power supply to allow portability:
source: https://www.youtube.com/watch?v=Pne1yKr3V_s
These cesium based clocks are the basis of GPS - corrections must be made to account for the GPS satellites speed and altitude.
Ytterbium based clocks run at much higher frequencies (518,295,836,590,863 Hz or 518 TeraHertz ?) than cesium (think light not RF) thus providing greater precision. But I never really thought about how they measure the frequency of light accurately. Veritasium goes into this at about 25 minutes into the video. The method they detail rang many bells (or tuning forks ?) for me. They (in effect) use a comb generator (hook one of my Pulser kits to the VE3DNL marker generator to do this at RF) and then measure the beat note between the ytterbium clock output and the nearest comb frequency - the equivalent kit is the Grandson of Zerobeat kit !
Pulser kit: http://wb9kzy.com/pulser.htm
VE3DNL kit: http://wb9kzy.com/ve3dnl.htm
Grandson of Zerobeat kits: http://wb9kzy.com/gzbrtang.htm
Obviously the precision / accuracy of the kits doesn't compare with the NIST gear but using a comb generator (and a receiver) to measure the beat note of two close RF frequencies is a similar concept to what NIST is doing with lasers, the ytterbium standard and an optical receiver.
Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm
These clocks are precise enough to allow at least an order of magnitude better measurement of the Einstein prediction of how gravity changes space-time.
source: https://www.youtube.com/watch?v=eyZEqSPeMwg
the NIST blog page on this experiment: https://www.nist.gov/blogs/taking-measure/putting-einstein-test-worlds-most-accurate-clocks
The original clock based tests (Hafele and Keating in 1971) were done with Cesium based clocks - those clocks have a signal with a frequency of 9,192,631,770 Hz or 9.1 GHz. Curiousmarc on Youtube has recently been refurbishing similar equipment to attempt to duplicate the initial experiments, the latest was fixing a power supply to allow portability:
source: https://www.youtube.com/watch?v=Pne1yKr3V_s
These cesium based clocks are the basis of GPS - corrections must be made to account for the GPS satellites speed and altitude.
Ytterbium based clocks run at much higher frequencies (518,295,836,590,863 Hz or 518 TeraHertz ?) than cesium (think light not RF) thus providing greater precision. But I never really thought about how they measure the frequency of light accurately. Veritasium goes into this at about 25 minutes into the video. The method they detail rang many bells (or tuning forks ?) for me. They (in effect) use a comb generator (hook one of my Pulser kits to the VE3DNL marker generator to do this at RF) and then measure the beat note between the ytterbium clock output and the nearest comb frequency - the equivalent kit is the Grandson of Zerobeat kit !
Pulser kit: http://wb9kzy.com/pulser.htm
VE3DNL kit: http://wb9kzy.com/ve3dnl.htm
Grandson of Zerobeat kits: http://wb9kzy.com/gzbrtang.htm
Obviously the precision / accuracy of the kits doesn't compare with the NIST gear but using a comb generator (and a receiver) to measure the beat note of two close RF frequencies is a similar concept to what NIST is doing with lasers, the ytterbium standard and an optical receiver.
Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm
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