4 ms·

I'm also sharing some common knowledge among electronics enthusiasts, but other readers may find it interesting: besides these custom top performance ones in p

I'm also sharing some common knowledge among electronics enthusiasts, but other readers may find it interesting: besides these custom top performance ones in physics labs or miniature chip-scale ones for embedded applications, it's worth pointing out that "regular" cesium atomic clocks are readily available as standard commercial products, anyone with enough cash can just purchase it today and mount it on a rack in your server room tomorrow. The workhorse in the industry is the Hewlett-Packard^W Agilent^W Symmetricom^W Microsemi^W... oh I meant the Microchip 5071A Cesium Clock Primary Frequency Standard. [1] The TAI & UTC time are literally powered by these clocks - more than half of the atomic clocks in national standard labs are Microchip 5071As. Also, if much lower performance is acceptable, a rubidium frequency standard is extremely affordable. You can get second-hand modules (usually retired from base stations) for just $200. All they do is outputting an extremely accurate 10 MHz reference frequency, you can use a frequency divider to get an 1 PPS signal and drive a mechanical clock, or connect it to your oscilloscopes, spectrum analyzers, or frequency counters as an external timebase, or time a digital clock using a microcontroller, many interesting possibilities. And of course, if you have access to an outdoor radio antenna, you can outsource the task of generating an atomic-accurate frequency to a government's shortwave radio station or GPS, your tax dollar does the rest. [1] https://www.microsemi.com/document-portal/doc_download/133269-5071a-datasheet https://www.microsemi.com/document-portal/doc_download/13326...

nullc 5y ago
The rise of GPS clocks has really killed the commercial market for cesium beam clocks-- the 5071 is a design over twenty five years old. It's a fine piece of engineering (I have three, two I obtained broken and repaired) but its age is starting to show, including the fact that it is phenomenally expensive to get replacement tubes for (the tubes are limited life). Similar is true for rubidium standards, though there are some somewhat more modern models-- though since they aren't primary standards most places that use them will still use GPS to keep them on frequency. A primary standard like a 5071 can internally compensate for every major systematic effect and so they can autonomously derive the second without external calibration. Telecom rb's can't self-calibrate for their gas cell pressure. All this has lead to a worrisome dependence on GPS just as a precise source of frequency. Hopefully in the long run we'll see single chip optical clocks with GPS-clock beating performance at competitive prices-- if they got even close to GPS they would rapidly displace it, as the need to put up an antenna for GPS is a real nuisance, and GPS jammers are a sadly too common source of trouble.
- wbl 5y ago
  It's a pain to get the top of second calibrated on a ceasium beam clock.
  - nullc 5y ago
    Who doesn't like taking a road trip to Boulder Colorado? :) The 5071a even has internal batteries.
    - schoen 5y ago
      I know the NIST Time and Frequency division is based there, but what would you do in person once you got there? Do they have a service of some kind to help synchronize things in person for visitors?
      - deleted 5y ago
        [deleted]
      - nullc 5y ago
        Prior to the widespread use two way satellite time transfer (and secondarily GPS) for this purpose ( https://www.microsemi.com/document-portal/doc_view/133433-working-application-of-twstt-for-high-precision-remote-synchronization https://www.microsemi.com/document-portal/doc_view/133433-wo... )-- taking an atomic clock on a road trip was the standard way to obtain the second: https://ntrs.nasa.gov/api/citations/19820012622/downloads/19820012622.pdf https://ntrs.nasa.gov/api/citations/19820012622/downloads/19... There were even more portable units built specifically for this time transfer purpose. I don't think NIST has a regular service for this anymore, but since they do offer a host of calibration and verification services, I'd be surprised if you couldn't road trip a clock to obtain the second... at least for a price. I've seen some publications on transportable optical clocks in recent years, which I assume are motivated by validating newer higher precision TWSTT and fiber time transfer techniques.
        schoen 5y ago

nullc 5y ago

The rise of GPS clocks has really killed the commercial market for cesium beam clocks-- the 5071 is a design over twenty five years old. It's a fine piece of engineering (I have three, two I obtained broken and repaired) but its age is starting to show, including the fact that it is phenomenally expensive to get replacement tubes for (the tubes are limited life). Similar is true for rubidium standards, though there are some somewhat more modern models-- though since they aren't primary standards most places that use them will still use GPS to keep them on frequency. A primary standard like a 5071 can internally compensate for every major systematic effect and so they can autonomously derive the second without external calibration. Telecom rb's can't self-calibrate for their gas cell pressure. All this has lead to a worrisome dependence on GPS just as a precise source of frequency. Hopefully in the long run we'll see single chip optical clocks with GPS-clock beating performance at competitive prices-- if they got even close to GPS they would rapidly displace it, as the need to put up an antenna for GPS is a real nuisance, and GPS jammers are a sadly too common source of trouble.

wbl 5y ago
It's a pain to get the top of second calibrated on a ceasium beam clock.
- nullc 5y ago
  Who doesn't like taking a road trip to Boulder Colorado? :) The 5071a even has internal batteries.
  - schoen 5y ago
    I know the NIST Time and Frequency division is based there, but what would you do in person once you got there? Do they have a service of some kind to help synchronize things in person for visitors?
    - deleted 5y ago
      [deleted]
    - nullc 5y ago
      Prior to the widespread use two way satellite time transfer (and secondarily GPS) for this purpose ( https://www.microsemi.com/document-portal/doc_view/133433-working-application-of-twstt-for-high-precision-remote-synchronization https://www.microsemi.com/document-portal/doc_view/133433-wo... )-- taking an atomic clock on a road trip was the standard way to obtain the second: https://ntrs.nasa.gov/api/citations/19820012622/downloads/19820012622.pdf https://ntrs.nasa.gov/api/citations/19820012622/downloads/19... There were even more portable units built specifically for this time transfer purpose. I don't think NIST has a regular service for this anymore, but since they do offer a host of calibration and verification services, I'd be surprised if you couldn't road trip a clock to obtain the second... at least for a price. I've seen some publications on transportable optical clocks in recent years, which I assume are motivated by validating newer higher precision TWSTT and fiber time transfer techniques.
      - schoen 5y ago