How an Atomic Clock Really Works: Inside the HP 5061A Cesium Clock
ฝัง
- เผยแพร่เมื่อ 5 ต.ค. 2024
- I finally get my hands on what I consider a holy instrument: the HP 5061A Cesium clock. We'll turn it on and play with it, of course, but I'll also explain how it works in more details than most videos, both the quantum physics principle and the HP implementation. What makes it tick is just mind blowing.
See continuation in part 2 here: • How an Atomic Clock Re...
Cody's Lab Cesium video: • Isolating Cesium Metal
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You should do a series interviewing some old engineers from HP, Tektronix, etc. to know the stories behind these designs. Probable a few may still be around. Great work and keep bringing these engineering marvels back to life and for us to enjoy them.
Unfortunately, they probably have non-disclosure agreements that prevent them from talking about anything they did for the company.
I think some engineers do interviews for the Computer History Museum (some are posted to YT on the CHM channel), but it is difficult to find them for the same NDA/IP reason. The CHM posts interviews of people labeled as "the verbal history of (insert individual's name)." If you know the person's name, you might find something, but you can't search based on the products, company, position, etc., directly.
My favorite interview on there is the one from the Motorola 68k design team (a must watch, but beware it's 3.5hrs long). It's one of the few interviews that actually has the company/product in the title for whatever reason.
It's kinda sad really. Someone should silence the lousy lawyers and marketing morons so that the younger generations, like myself, can gain a greater appreciation of the stories of our past. The silencing of company employed inventors and engineers is basically stealing a future generation's foundations in favor of the irrelevant, half baked marketing of the present. NDA's, copyright, and trademark should be like patents, with an expiration date relative to the individual's employment history. A person that spends decades at a company, is a shareholder in the history of the company with as much right to tell their versions of stories as much as any psyco marketing spin doctor. No technology, product, or process from 20+ years ago is financially relevant to the present. If it is, forcing innovation and progress is not a bad thing. Regardless of the criminal state of Right to Repair in the US political clown show, any product currently made can be reverse engineered abroad. Intellectual property is not very valuable in the sphere of the capable. It's inflated valuation in the English speaking world is a devaluation of the inspiration it should instill in future generations. People make companies, companies do not make people.
Soapbox...sorry...
@@UpcycleElectronics The verbal histories collected by the Computer History Museum are absolutely priceless. Specifically for the history of semiconductor industry, "History of Semiconductor Engineering" by Bo Lojek also provides some interesting perspective, often very different from conventional corporate history accounts.
@@cogoid
Thanks.
Funny, I didn't realize the reference is a book. I was trying all kinds of crazy things looking for a CHM upload with Bo Lojek. I gave up and wound up spending the evening watching "Pioneers of Pioneer Computers" Pt 1&2 before searching the web and seeing the book. The 'PoPC' is another good one ...It's funny how many dudes got all bent over von Neumann's name attributions in early digital computing :-)
@@UpcycleElectronics Another really great book is "Crystal Fire: The Invention of the Transistor and the Birth of the Information Age" -- it gives a very detailed behind the scenes picture of what went on in the Bell Labs, and how a series of both mistakes and deliberate efforts have lead to the discovery of transistor. Not quite as technical as Bo Lojec's book, but really well written.
@@UpcycleElectronics Do NDAs really last that long? That's pretty shitty.
This brings back memories from my childhood. My dad, Dr. Leonard S. Cutler (1928-2006) led the team that developed this clock. He is the man with his back to the camera in the photo at 1:38. Back in the 1960s and early '70s he sometimes took me to Hewlett Packard at 1501 Page Mill Road in Palo Alto, California on the weekends. As a young boy I got to see the research and development of the Hewlett Packard cesium clocks. Later on, development of the cesium clocks was moved to Hewlett Packard's Santa Clara plant. Eventually Agilent sold their atomic clock business to Symmetricom. After my parents passed away, I inherited their house, and in one of my dad's old storage rooms is a four-drawer file cabinet that still has most of his notes and documentation for the 5061 and the later 5071 cesium standards.
Well, kudos to your Dad! Can you contact me through the link under the video? Are you still in Palo Alto?
@@CuriousMarc I am not actually in Palo Alto, but close. I live in Los Altos Hills fairly close to Stanford. You can send me an email to the address in the "about" section in my channel.
Cool,
Measure the time an electron's circuit around the nucleus of a cesium Atom. That equals 1 second.
😊
Really interesting and well explained. I never knew how complicated the process is!
Thanks Ben!
@@CuriousMarc next step ben will do a DIY version of this clock
All hacking requires convolution. We are hacking time
One of the more interesting insights I've ever picked up pertained to LIGO: Being so sensitive, it is an everything-detector and the hard part is filtering out everything except the real signals. Cesium clocks are similar: building the basic clock is "easy," but it is also a detector for the local E and B fields, and their gradients, and the local temperature, etc, etc... The bulk of primary reference clocks largely consists in stabilizing/knowing all these things so that the systematic uncertainty can be reduced to the level of 1e-15.
@@CuriousMarc your video's background music isn't loud and annoying enough
Back when HP made the best instruments in the world.
I always thought when they spun off the test equipment it should have kept the HP name, not Agilent.
@@dfmayes Same here. I tend to think of two eras: real HP and fake HP
23:02: Ultra-precision instruments in the foreground, bench grinder in the background.
OK, so...?
I don't know what kind of adjustments that bench grinder has but...
coarse.
Sometimes brute Force is the solution
You do notice Marc lined the table with paper and taped all the edges prior to setting down this incredible device 😉love this channel
You're saying a bench grinder is NOT an ultra-precision device?
Wow, I worked at HP Santa Clara Division for 25 years, R&D, Building these Units all the way up-to the smart hp 5071a cesium atomic beam, It was Ethereal! I enjoy every moment. Felipe Espinoza
Wow, that brings back a lot of memories! I was a development engineer in the Precision Frequency Standards (PFS) group at HP Santa Clara (CA) division then. That's where they were developed and produced. It was really interesting. I previously had worked on Cesium clocks at MIT when I was a physics student, then interned at a competitor company in New York and there learned more about both Cesium clocks and crystal oscillators. Worked on the successor product 5062 (? my memory ?) also.
That's actually really cool. I was the Service engineer for the 5334A in 1981 (I think that date is correct) and designed the troubleshooting and self test strategy for the unit! I was responsible for the operations manual and the service manual. At one time I had responsibility as the back up service engineer for the 5061.
@@brianbeasley7270 Yeah, some of those quality and serviceability aspects are still present in the early 2000s HP computer equipment I maintain. Sadly later company practices at HP and HPE have apparently ended this dedication to quality and honesty, making me look elsewhere most of the time.
I could listen for hours, to what you did back then.
Nice to see she still works. A year or so back I bought one of its great offspring an Ebay Rb oscillator. Also have a couple of GPS disciplined oven crystal oscillators running at 10Mhz. It cool to put them up on two channels of the scope and watch the phase difference. When you first turn on the Rb oscillator and it's warming up the phase sweeping back and forth looking for the lock. Then it gets closer and closer and finally it just snaps into lock.
Just love the idea of owning something containing a "Physics Package".
What I found interesting is what I call phase breathing. Over a period of 10's of minutes the phase error may be rock stable then it will breathe and slowly drift then be stable for a while again then drift back. Almost never slips more than one clock cycle at 10Mhz. What I would like to know is how much of this slow drift is from the GPS vs the Rb oscillator. With just two instruments I can't tell who is drifting. Because the drift is relatively short term its most likely the GPS. Got enough coax to run me a 5MHz reference to my Sunnyvale lab?
Craig
That's gold 😂
@Craig S
You don't need a coax. Just shine a laser beam across town at night. Switch it on and off at 10 MHz. 👍
@@acmefixer1 If its a big enough beam, we can run it in the daytime too =)
The 80 version of the HP Cesium clock was used in military satellite communications terminals to provide both timing and frequency references. I used to daily do comparison time offset measurements between the clock in my terminal and the clock on the distant end terminal. We'd send those values off to the Naval Observatory weekly and periodically receive correction factors to load into our clock. The corrections were intended to eliminate the time offset between clocks. It was a blessing when Techtronics came out with scopes that would allow us to accurately measure the offsets vice having to use multiple freq counters to extrapolate the offset values.
Those were great clocks not a lot of trouble with them.
The German equivalent of WWVB (DCF77) apparently uses a bank of 3 of these HP units to keep everything right on the mark, checking against GPS for synchronization between the two alternative transmitter sites.
@@johndododoe1411 These museum clocks may be good for hobbyists but not as a national standard. DCF77 is controlled by the PTB (NIST equivalent) at a precision
My physics lessons at school were one of the more interesting parts of my education - however - this content is on another level - fascinating and I would have thought perfect to trigger new interests from anyone who watches.
Should be part of curriculum's everywhere.
I agree, a great "show and tell", not just the theory but the practical application of the process..👍👍👍
I dunno how deep into the technical aspects of physics you like to get, but assuming you preferred the general theories to the hard maths, you should check out physics for future presidents. It's a lecture series from UC Berkeley you can find on TH-cam. I loved it because it's not too heavy on the math, so it's easy for anyone with even a rudimentary knowledge of physics to follow.
If you prefer something more akin to a standard physics class, I'd recomment MIT's physics 801, 802 and 803 lectures. The ones presented by Walter Lewin are especially good. Though I found a lot of them require at least some knowledge of calculus and algebra to follow. But you can still appreciate them without knowing the math.
Enjoy!
I absolutely loved this explanation. I knew spectral lines were related to jumps in the energy level of an electron, but I did not know they came in pairs because of electron spin. I also did not know the nucleus has a spin as well.
@@Fake_Blood I worked on an experiment at LAMPF using the hyperfine and nuclear spin coupling transition in a NMR detector. This brought back a lot of memories.
Fascinating video. That's the first explanation of a caesium clock I've ever seen that I fully understood from beginning to end.
The comments on these video's are fantastic. Love atomic time. Grew up with friends whose dad's worked at the Dept. of Commerce in Boulder, Colorado.
The best was my neighbor, who was an engineer at HP Loveland. This guy unloaded a basement full of electronics on me when I was about 12 years old, because he was moving to a new home. Lifelong radio hobbyist and electronics tech because of it.
Was surprised to see the name Agilent inside that box. I guess they serviced this sometime after 1999?
We think that’s the case, and the reason why it still works.
@@CuriousMarc yep, tubes only last ~20 years. Mine is from the Datum side of Symmetricom, and I'm still not sure if it's got a dead tube or electronics (my test gear generally stops below 1GHz, haven't yet acquired the bits I need to figure it out). For most of 2018 it lived at my partner team's office in Sunnyvale where I used it as a monitor stand before I got it shipped home.
@@laptop006 if you don't want it and just want to give it away I'll gladly take it off your hands ::)
Oh wait, that's a high perf tube, they're normally more like 10 year lifetimes IIRC, very good luck with that.
Agilent is what happened to the _real_ part of HP that meant something. It is where the true heart of HP went.
The nod to _Cody’s Lab_ gets my hearty approval. It’s nice seeing excellent science educators acknowledging each other. Now I need to go catch up on Cody’s recent videos.
He did a good video on ion pumps also iirc.
Lived with these as a Loran technician for the U. S. Coast Guard. I was the project manager in the early 2000s for the upgrade to the Agilent clock.
This was fantastic. I never knew how these things worked and I believe you did a fantastic job explaining it. Suggest a Kickstarter when this clock runs out of cesium. I'd kick in.
This was very cool! The first thing I noticed when the cover came off was the "Agilent" logo, and I was confused due to the age of the instrument. When the Lissajous figure was stationary, and the scope traces were precisely in phase - wow, that was something. The scientific explanation sounded pretty solid to me, but it has been 37 years since I had physics and 39 since I had chemistry.
Coast Guard LORAN-C stations used CAQI-5061A (CAQI=HP, some sort of manufacturer designation) for so many years... Can't tell you how many daily log readings I took on them over the years- Each station had an "Operate" or #1, a "Standby" or #2 feeding an associated timer and other gear that could be "dirty" switched in the event of a failure or "clean" switched by aligning the phase of the output 5mhz, and a "tertiary" that could be patched into either #1 or #2 position in event of a failure. Each freq standard had a log book with daily readings that travelled with it- on the rare occasion of a failure it would be returned and repaired, and the log book would stay with the standard. Each secondary station's standards were compared to the master station's standards and drifts were handled with phase microsteppers, which if I remember correctly adjusted to six decimal places below a nanosecond, and longer term were compensated with "C-Field" adjustments. It was some time after 2003 - 2005?? when the stations timing and control equipment was "modernized" that the 5061s were replaced with 5071s ? I retired from my last station in 2008 and the program ended in 2010. I feel a little bad I don't remember more, but it is amazing the things that stick in one's brain. I believe the story that had been around forever was that free-running, in a perfectly stable environment, the 5061 would drift about one second in 30,000 years. :)
I should have said a clean switch was done by phase matching the 5mhz output of the two timers, not the two cesiums.
You are correct, the adjustments were made in femtoseconds :)
CAQI was BuSHIPS (Bureau of Ships) code for HP.
If I’m not mistaken, the advertised stability of the HP5061A is 1E-11, 1 microsecond a day, which translates to 1s every 3,200 years. Baby sitting your 5061 carefully (Zeeman line tweak anyone) or upgrading to the 5071 might have garnered another order of magnitude though that would put it in your range. Current lab clocks are way past 1E-15. Mind-boggling.
Amazing to consider that this box of tricks was built a mere 50 years or so after Rutherford formulated his model of the atom (around 1911). Thanks for the video!
Marc, you always pause just briefly before you say "H.P." it's almost like you're preparing to speak a powerful magic word or utter the name of God or something. ;)
Thanks for the Quantum Mechanics explaination, you managed to explain it better than a lot of the physicists I have listened to.
That oscilloscope was... ... ... too modern! ;)
H.P. Use to be The GOD of test equipment. The Name is more then special. LOL Still is in my heart.
I agree, in the 1970s HP was mentioned in reverent tones. Similar to the milspec HF radio used by amateurs, the Collins... (sinks to knees).
The Navy's AN/BSQ-4 Precision Frequency Standard contained two of these clocks. They were so reliable we almost never had to do anything with them but monitor them.
They lose one second every million years....
I’m literally glowing from all this lovely new knowledge in my head 🤓
Leo Bodnar makes some very good GPS clocks. I treat the other ones as suspect.
Now, going back in my personal time machine or at least memory I visit 1966. I was working at a University of Michigan lab. We were measuring partial pressures of various atmospheric constituents at high altitude. We were using an Omegatron, a U of M invention I believe. The measurement was a similar tune for peak. It was at low enough frequencies to use little IRIG electronically variable frequency oscillators. They tuned it to peak in the lab. Um, later on they tuned it off peak a little. More on this later.
The use model involved tossing a payload into a Nike Ajax nose and seeing what happens. They quickly learned that their magnets did not take well to the shock of the launch. (It's later.) They attempted to compensate for this by tuning off frequency a little hoping they'd arrive at the peak after launch. They decided that would not work. So they adopted the same sort of strategy as used in the 5061a. They used got fair accuracy, not what they intended. That is where I entered the picture. A little analysis later I figured out their demodulator developed biases that were not nice constants due to the sinewave sweep over the peak. The even harmonics were doing this. Betcha many reading this know what I did next. I changed the 30 Hz (if memory serves) sinewave sweep to a squarewave step to either side of peak. The second harmonic errors vanished, of course. The calculated error of the level of the peak fell to so close to zero I never published the real figure. I published figures for wildly imprecise components. Set it up in the lab and the error in free fall was reduced to parts per million from parts per 100s.
I saw applications for this. I may be clever with electronics; but, I could not and still cannot sell everlasting solar powered refrigerators to people living in the Sahara desert. The person I worked for dismissed it with a ho-hum. In found somebody else had finally suggested this in the 1970s while reading a Proceedings of the Frequency Control Symposium. I felt simultaneously vindicated and cheated. I also swore off bothering about patents after that. The patent I do have, under a married name, was an accident. I was blind sided. Later on I was responsible for the frequency synthesizer design for the Phase IIb GPS satellites, the ones with two Rb and one Cs frequency standards. But that's another story.
{^_^}
I am astonished by the sheer amount of cool toys you guys get to play with! Good work!
I can't upvote this enough. Thank you for the clear and concise explanation!
"in soviet Russia you do not measure atom, atom measures you"
Had one in a military installation. It was set using the audio shown on an oscilloscope to sync it's 1 second pulse with the WWV tick. We had a delay we used for both the delay of the receiver used, and propagation delay from Fort Collins Colorado, so the clock would tick just before the signal on the radio was received. This was in the late 1970's before GPS time distribution became the new standard. Looks like we got one after they were out a while and proven in the field and the price reduced.
On one shift, one of the new guys made the mistake of changing it for daylight savings time.. It was supposed to remain on UCT or GMT.
When it was first installed, and set, it was installed on the dayshift, and I had the swing shift. I had to call my supervisor as it went into alarm for low battery. It was jumpered for 240v, but was plugged in on 120v, so the battery died on shift. It was New, Expensive, and thus I was not permitted to touch it. On watch just checked for the drift between the clock and WWV. Not touching it, I did check the setting for the line voltage. It did die on shift for low battery because I was not permitted to touch it.
I got to work with one when it was cutting edge and just out on the market. Nice piece of history.
VERY nice! Takes me right back to my career working in electronic calibration laboratories in the 1980's and 1990's. Just discovered this channel and ... Subscribed!
Instead of Lissajous, better use Time Interval measurement on your 5334B, between 1pps of Cs clock and GPS clock (or OCXO), and use TimeLab over GPIB control to collect the phase shift.
Data collection and averaging over several hours / a whole day only will mitigate any GPS signal jitter, and only then will give you the necessary resolution to calculate the accuracy of the 5061A.
GPS receivers usually need several hours, or 1-2 days to really get stable, i.e. to learn the behavior of their internal OCXO (if available) vs the jittered GPS time information. So your momentary snapshots of phase (out of the Lissajous figure) is probably useless. Cheap GPS units probably never manage to achieve a short term stable time signal, (use ADEV analysis) compared to e.g. the Trimble Thunderbolt.
Yes, but watching Lissajous figures is much more fun.
I was really pleased to see lissajous being used for a practical purpose rather than just "ooooh pretty" which is all I've ever done with them.
@@edgeeffect Watching (again) Lissajous figures might be fun at first sight, but they become very soon boring, and not practical at all, when you try to adjust atomic clocks.
Simply calculate, how fast the figure will rotate once (180° or 50nsec phase shift) for a feasible 1E-9 frequency accuracy adjustment of the OCXO inside the 5334B, that'll be 50sec..
That's still practical, but when you try to adjust an Rb clock, which might be stable / precise to 1E-11, this will take 5000 sec already.
If you try to resolve 4° only on the Lissajous figure with your naked eye, equivalent to 1ns, that'll be 2 minutes already.. very boring .
When you would try to adjust a hp 5061A Cs standard to 1E-12 (standard tube) or 1E-13 (option 004 tube, as in the video), that minute change of this figure would require up to several hours, and everybody doing this experiment would fall asleep soon, I fear.
There's also another problem with such cheap GPS receivers, probably w/o a disciplined OCXO inside, that is the GPS signal jitter on the order of 1E-10 / sec, 3 order of magnitude above the required stability .. you would never come to a conclusion by the Lissajous method.
First result for cesium clock, 100% the exact level of detail i was looking for!
I remember having one of those at Bell Northern Research in the early 90s. IIRC it was used as a reference clock for validating the VCXO frequency used by telephone switches for trunking.
Love the hyperfine transition discussion. So fun. Thank you.
FBI Top 10-Things you don't want to mention in a youtube video: "Oh, I like those things! The atomic bomb is on the left, the detonator is on the right and the crypto things over there..."
Another great video, thanks! When all this is over, I'd love to come over to the Computer History Museum and take a close look at the IBM 1401 and the other cool stuff there. Maybe next year... Stay well!
wow supplier catalogues that list prices, that's novel. I'm used to "SEE DEALER FOR A QUOTE" on everything
"SEE DEALER FOR A QUOTE" -- I hate seeing that so much, always so disappointing to run into that.
Whenever I see that I move on, it's an instant "Look, if you need to ask you just can't afford it!"
@@Drew-Dastardly That's very true and usually they are right, I can't afford it! But sometimes my nosy self likes knowing how much things cost so I can dream!
I remember as a kid picking up an HP catalog at a Hamfest. A hardbound book as a catalog! All those treasures that were buried within it..
I have such a hell of time following exactly what is being talked about in these videos. Im a musician, not a scientist. However, I find this stuff super fascinating and despite my issues fully understanding everything, I watch all the way through.
Great work :)
We had one of these cesium clocks on our satellite communication's facility back in the eighties. Filled with dozens of cables connecting all the distribution amps together, all of which didn't like to be touched.
When I was an undergraduate physics student in Chicago in the mid1970's, my (very nice) parents bought me an HP35 calculator. One very hot day, the case melted inside my car. I took it to the nearest HP repair facility (in Niles, Illinois); they swapped shells for me at no charge (but broke one of the battery compartment clips and destroyed the back decal, unfortunately). Afterwards, the repair tech took me into the back to show me their brand-new HP cesium clock. Amazing!
A year later, I did a summer internship at Argonne National Laboratory, where I put together a data acquisition system from shipping containers full of fresh HP2016 parts. They had allocated the full summer for me to do so; I had it up and running (BASIC interpreter and TREK73 game) by the end of the week :-)
I never understood the principles of the caesium clock until today. What a wonderful, clear, explanation.
Thanks, mate, from Chris, in Tasmania.
I learn so much from you and your friends Marc and with such ease from your superb descriptions. This is the next best thing to being in your lab with you. All the best.
> But what makes it tick is just mind blowing.
I see what you did there.
The degree that humanity has come to understand the physical world never ceases to amaze!
when you say that your mind will be blown and when I watch it it's like it makes total sense to me
That particular gpsdo gives a green light before it is locked. It also takes forever to get close to freq. The bigger one with the green pcb front cover only gives the light when it is locked, but the lock is a few millihz off. You cant use any of these units for timing, but they’re ok for freq standards for ham radio which is what they’re designed for.
Get a Trimble Thunderbolt.
I've always wondered how atomic clocks work, and your explanation of how they utilize the Stern-Gerlach apparatus finally put it all together for me, MANY thanks !!!
Great explanation. It is amazing this device was commercially available only a few years after the LASER was invented! Nowadays atomic clocks take advantage of lasers for optical probing of hyperfine transition in Cs vapors. Atomic beams are no longer used. The clock can therefore stay operational for many years without need for "refueling".
Cesium clocks run for decades between tube swaps.
That looks like a day spent well!
I had a couple of friends who worked for HP in the Rohnert Park area, it seems like it was the microwave test equipment division mainly, and I got the tour on one Saturday night, walking through production and testing, into the anechoic chamber, etc.
Later they showed up to work one Monday, to the "Company With No Name", because HP had spun them off, but without a name! They were no longer HP, just "...."
Not even "The Artist Formerly Know As HP" LOL
After some discussion, they decided to let the employees choose a name, and so suggestions were made, and then they started voting, and finally ended up with Agilent.
So yes, that was certainly last worked on since then, so that '89 date isn't the date of the tube.
The Rohnert Park (actually Santa Rosa) location of HP was (still is?) the communications test instrument division. It's still an incredible place to visit. They have the same old HP instruments I collect displayed on glass shelves. The engineer's cubes are full of the same instruments, still being used today.
FYI the power connector shown at 3:15 is a Mil C 5015 connector with what I think is the 14S-1 connector arrangement. Due to their robustness and utility they are still being made and are available from the likes of Digi Key.
Very cool! I've read the manuals for the HP cesium clocks and thought those were fascinating pieces of equipment. It's too bad the cesium tube has a limited life span, but glad to see you found a working one.
Always a pleasure to seen some vintage HP goodness.
These guys were the top of the best in groundbreaking lab tech. The fact HP recessed to a second zone home PC and disposable inkjet printers manufacturer puzzles me. Rise and fall of empires...
Anyway Agilent was spun off HP in 1999 so that caesium tube is pretty recent.
I used to work for HP. It’s beyond saddening to see what it has become. Carly Fiorina flooded the company with cheap 3rd worlders. Damn her to hell.
@@trainingtheworld5093 :(
And then Keysight spun off Agilent. I believe that the Time division was either spun off or purchased to becomes
Symmetricon, which was then bought by Microsemi, which was then bought by Microchip.
Also, I believe that the crystal oscillator was used to clean up the Cesium clock. Cesium clocks have great accuracy, but they don't have very good phase noise. Crystal oscillator aren't nearly as accurate, but they have good phase noise. By locking them together you get the best of both worlds. At least that is what I remember.
The most satisfying 8 zeros I've ever seen on TH-cam.
I love the fact that there's an atomic clock and a bench grinder on the table at the same time! Probably not that ususal of a setup 😁
This made me understand how a cesium clock actually works. Amazing explanation!
Thanks for posting Marc
What a fantastic video Marc! Excellent discussion and explanation of this type of clock
I used to play around with precision clocks. Every time you plot them on a scope together, and see them hardly drift, it's a magical moment. That you can do these things in your own home is incredible. (I was using a rubidium clock, but those have about the same accuracy as a cesium clock from that era.)
The man's humor is first class. At 3:19 he remarks on the unique power cord: "It's really annoying if you don't have it" Happens to everyone when they measure orbital time difference with a Cesium Clock.
Locked to atomic time. Huzzah! Coolest sound effect in a TH-cam video ever. Kudos!
That was pure geekville and I loved every second.
because of relativity, the two clocks be slightly different frequencies. (the one in the lab and the one in the satellite) over time, the the Lissajous pattern should very slowly drift. the drift should be measurable by taking a time lapse of the scope, and calculating the phase error, and thus how fast the satellite is moving relative to the clock in the lab. looks like the ones on the satellite should be running 7uS slower per day hurtling through space at 14000 km/h (says google). at 10MHz, this means 1 cycle of it is .1uS, so over the course of the day the lab clock and the satellite clock should slip past each other 70 times, or about 3 times an hour. if my math isn't completely off, that is. it'd be an interesting experiment to determine how fast the speed difference is by observing how long it takes the pattern to rotate once.
Except the GPS satellite clocks and signals are already corrected for both special and general relativity, or the system wouldn’t work...
@@CuriousMarc It is true, of course, that GPS system is built with several relativistic effects taken into account. But the way in which this is explained is not always quite accurate.
Due to relativistic effects the clocks on the satellites do speed up relative to the clocks on the ground by about 38 microseconds per day. But that does not imply that the system would produce an equally large navigation error, *if* relativistic effects were not corrected for. The navigation depends not on the absolute time, but on time difference between signals arriving from several satellites. Because the orbits of the GPS satellites are essentially the same, the clocks on all satellites drift in approximately the same way, and the first order relativistic effects would, in fact, cancel out on their own from the time difference between any two GPS satellites. What *does not* cancel out, is the difference between relativistic effects experienced by different satellites due to slight differences between their orbits, etc. But the magnitude of these effects is a very small fraction of the 38us average drift, and the error would be far, far smaller than 10 km/day which is often cited by multiplying 38 us by the speed of light. GPS without relativistic corrections would be a system of very limited precision, but not nearly as useless as it is often portrayed.
@@cogoid Positioning is not the primary function of the satellite segment of GPS. Foremost GPS is a time and frequency standard. Software in your receiver is the only thing that makes it a positioning system. A time and frequency standard that doesn’t keep proper time or frequency isn’t terribly useful.
@@stargazer7644 I am not sure how your comment relates to what I have said earlier. If you are saying that the primary purpose of *Global Positioning System* is not navigation, that is not a defensible statement.
@@cogoid I'll try repeating it. "Positioning is not the primary function of the satellite segment of GPS." Your previous comment says essentially that the relativistic correction for GPS isn't really important because you believe the errors cancel when determining position. GPS is composed of multiple segments. The space segment consisting of a constellation of satellites, the ground segment, and the user segment. The space segment is nothing more than a constellation of atomic clocks and radio transmitters. The satellites don't know where you are. All they do is transmit very accurate TIME and FREQUENCY along with the orbital elements they get from the ground segment. The satellites don't figure out where you are, your receiver does that. There are quite a few devices such as the GPSDO shown in this very video that rely on the time and frequency broadcast from GPS sats. The entire wireless telephone network and wired Internet rely on standard frequency broadcast by GPS. These systems have NOTHING to do with positioning, and would not work without GPS. Yes, one of the functions of entire GPS system is to allow the user segment to determine their position. But the only part the GPS Space segment plays in that, is to broadcast accurate time and frequency. If the satellites didn't implement corrections to their timebases for relativity and other errors, they would be useless as time and frequency standards for all of the other uses of GPS.
The GPSDO normally needs a couple of hours, normally a day, to get its precision as it uses averaging.
Indeed it settled down after one hour.
Thats only true of good GPSDOs, many of these generic ebay units do not lock exactly on frequency.
The only thing that could make this better is a Nixie tube display in the black part :)
One day when I'm very old, I'm going to build a replica of one of these Caesium tubes and the necessary (and very tricky) magnetic C field system. I've got most of the hard vacuum kit, I can do a reasonable job with vacuum glassware, and the microwave and PLL are very simple these days. Caesium ampoules are easy enough to get hold of and I have some ultra-stable and well aged 10 MHz quartz double-ovened oscillators that can manage a few parts per billion stability without locking. I've already got some Rb references and several Quartz oscillators that are double-ovened and kept in a vibration-isolated rack case in a temperature-controlled enclosure. Also five GPS-locked systems. It's interesting to see the occasional GPS phase glitches. An amusing issue happens when two references are very VERY close to lock, sometimes they jump into phase-lock where one is injection-locked by tiny leakage signals from another, same as when two pendulum clocks lock when mounted on a slightly compliant mount. For proper time/frequency geeks, the Time-Nuts email forum is an absolute must.
10:10 Totally clear, in a "I could not repeat it, and I could not point at the parts, but it makes sense, and meshes with the tiny amount I understand about Relativity, and the even tinier part I understand about Quantums" way.
Supposed to be "working" from self-quarantine rn but actually just watching Curiousmarc youtubes 🙏🙏
* 19:15 -cesium clocks- rubidium clocks in orbit (or sometimes hydrogen masers). If I remember right these have smaller Allan deviations for shorter timescales than Cs which is good because the satellites get new correct time standards beamed up every day anyway.
They have both (or used to at least). From what I understand the advantage is that the Cs ones don’t drift and are the master references. The Rb are much cheaper (no high vac involved).
This stationary Lissajous pattern was just gorgeous.
Great overview of the clock’s operation. A few years ago, I ran across some open courseware videos, from UC Berkeley as I recall, on an attempt to make an atomic clock on the chip level in MEMS technology. I’m not sure if they managed to make it work. Isaac Asimov’s physics books provide an interesting overview of the basic theory behind quantum mechanics.
I graduated with a BS in physics and focused on astrophysicist, quantum mechanics and particle physics so I’m not shy in saying your explanation was poetic. Keep that up and you’ll give Neal deGras Tyson some competition.
Cesium clock is the ultimate surface plate. Our world is built on precision references. Thank you Marc for explaining the 5061A operation to us.
After all that crazy science, when you say "built in 68 repaired in 86, that's why it works" I thought that was some kind of quantum physics theory of reversal or something
Wow, the quantum bisector refolding the quasimanifolds
Thank you, no really, thank you for showing us this your channel is now officially my favourite channel
Thank you , this was excellent theoretics and lab work.
And all this time I thought an atomic clock was driven by radioactive decay of cesium(137)
Cesium just sounds radioactive.
CESIUM CLOCK needs its own Playlist...
Please....
while its running...
Just calibrate EVERYTHING
thanks
We used a variation of this model as part of the VERDIN VLF communications receiver back in the 80's. We never had one problem with it in the three years I worked on the system.
I really enjoyed this segmanet. The Hafele-Keating experiment was a test of the theory of relativity. In 1971, My law partner's brother, Joseph C. Hafele, a physicist, and Richard E. Keating, an astronomer, took four cesium-beam atomic clocks aboard commercial airliners. They flew twice around the world, first eastward, then westward, and compared the clocks against others that remained at the United States Naval Observatory. When reunited, the three sets of clocks were found to disagree with one another, and their differences were consistent with the predictions of special and general relativity.
This begs the question of how do you calibrate the first caesium clock without any other accurate atomic clocks?
You don’t calibrate the frequency of a cesium clock. It is a primary reference. It uses the atomic resonance to set its frequency, and that only changes in response to relativity. If you compare two clocks in different gravity fields they will run at different rates, but that isn’t because the clock is wrong, it is because time flows at different rates in different gravitational fields.
Chapeau Monsieur curious Marc! This is by far the best explanation of this fascinating piece of equipment I´ve ever seen! If I could i´d give 5 thumbs up!
Since both Rb and Cs are usable for making time references, could we go further up the group and make less accurate clocks with K, Na, etc?
Don’t know about accuracy, but hydrogen frequency standards are well used on board of navigation and scientific satellites.
@@bakagaijin7452 Hydrogen masers are the gold standard for short-term stability in the RF domain but they slowly drift over time (
Maybe using rock salt for the sodium??
@@acmefixer1 Its already ionised at that point so the tube in that clock wouldnt work. Unless you mean extracting the pure metal from the salt? You'd need to purify it first. There's better sources for sodium chloride than rock salt.
Rb and Cs clocks have somewhat different operating principles. There is a serendipitous coincidence between energy levels of different isotopes of Rubidium which makes it possible to make a very simple atomic clock. If simplicity is not required, many different elements can and have been be used for making very high performance frequency standards -- but these are research instruments. In commercial use, Cs and Rb dominate, with Hydrogen masers also used for some applications.
Awesome. Back in the '60s, even the PLL synthesizer must have been pretty bleeding edge technology.
Harmonic generation in PLLs actually has some more down-to-earth applications as well, e.g. there used to be a few high-end FM tuners that would lock their mechanical-varicap-tuned LOs to a 50 or 100 kHz frequency grid this way. This way they would combine the better frontend selectivity of mechanical variable capacitors with the frequency stability of PLL tuned sets while still keeping phase noise at bay (almost all early PLL tuners were afflicted with more or less high levels of phase noise, degrading their maximum S/N).
I also thought that microwave and PLLs and frequency synthesizers were science-fiction in the 1960's. That's until I looked at the telemetry radars and transponders in Apollo. Then my jaw dropped. It's absolutely chock full of these things, some running at 9 GHz. BTW, this HP clock was installed just in time in 1968 to serve as the deep-space network master clock for the Apollo 8 mission.
That's twice I've seen Marcel in a video and twice where I thought: "what's the singer and bassist from Carcass doing here?". He's hiding his Scouser (Liverpudlian) accent very well, lol
Nice of him to bring some 'Toys' around for you to play with, Marc.
Amazing science, I never got properly before. You are a great teacher
I managed to get my hands on a Rubidium frequency standard used for Omega Navigation back in the day. Similar principles but a bit simpler.
It used a rubidium lamp to shine photons through a cavity containing rubidium ions. The cavity had a waveguide subject those ions to GHz frequency but it was dithered at 150 Hz rate by a triagonal wave making it sweep like FM. As that RF sweep went through that hyperfine transistion frequency the ions would then absorb the photons from the lamp and a dip in light intensity was detected after the cavity. This dip was tracked to discipline the 10 MHz crystal oscillator.
Apparently it might loose 1 second after 3000 years - Good enough for me
This chanel is getting better and better! :)
Thank you for your efforts to explain this experiment.
I actually fell asleep at ~7:30 minutes, no joke. I'm currently rewinding to watch again. I actually really appreciate it when people tell the history of science; how things were discovered.
Lol around 16:00 minutes you read out two separate Hz measurement numbers wrong in a row. Lol. Must have been a long night hahaha.
I love Marc, "Atoom measures you"
~2:58: "The cesium doesn't weigh very much..." :D :D
Beautifully explained, thanks!
I might need to watch this one more than once.
In US Air Force Precision Measuring Equipment Laboratory we had one. It had to have a yearly touch up on the frequency due to the slight drift, that difference between -11 and -12.
Ah, that C-field to adjust the Zeeman line. We have not done that yet.
I saw your interview on Gizmodo, very cool! I also saw the 1401 you restored at the CHM, really awesome.
What an absolute beautiful pice of equipment.
I was going to mention the tube replacement! Score!
Agilent is a pretty recent name...It came about in 2000. The test equipment division was spun off again as Keysight in 2014.
23:07 I can't tell if that pattern is tumbling end over end (rotating on horizontal axis) or if it's spinning on the vertical axis...like one of those mind illusions!
Well, my brain definitely does hurt now! But only because this was so fascinating I couldn’t stop watching!
The design of the machine is interesting, but perhaps more interesting to me is that it's the first explanation I've seen of the derivation of the standard for defining the second.
I don't know about the 'usual' PCB-faced GPSDOs that are on ebay like that one, but I have a very slightly fancier one that exhibits instability for a bit when the output 'load' changes significantly, to the point where I could connect/disconnect a device on the timing circuit and watch it hunt on the scope.
23:02 you can change the rotation of the image on the scope clockwise/anti clockwise just by thinking about it, try it!
My friend wanted on the clock team in 1974 for the Air Force PME Lab AKA PMEL which worked in.