CuriousMarc - 2020-03-20
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: https://youtu.be/xTy1kY_wtsY Cody's Lab Cesium video: https://youtu.be/rSJGwnERIVU Our sponsor for PCBs: https://www.pcbway.com Support the team on Patreon: https://www.patreon.com/curiousmarc Buy shirts on Teespring: https://teespring.com/stores/curiousmarcs-store Learn more on companion site: https://www.curiousmarc.com Contact info: https://www.youtube.com/curiousmarc/about Music Credits: Crinoline Dreams by Kevin MacLeod (www.incompetech.com) Scott Joplin's Nonpareil Rag by Scott Kirby (http://scottkirby.net/)
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
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.
HP: The serial number looks like a price tag, and the price tag looks like a serial number. But no doubt, the old stuff is better than anything on the market. Sadly, these days, I don't trust it much.
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.
@Brian Beasley 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 have a friend who wanted one of these since he was a kid... and got it a few years ago, on Ebay, of course.... getting the first one fixed was mind-bending... then he got a few more, at one point we had 3 cesium clocks, a rubidium, and a GPS disciplined clock all running on his workbench.... did the Lissajous on his analog scope... went to dinner, came back, nothing had moved.
I now feel fully qualified to call myself a quantum mechanic after the 3rd successful repair.
Getting locked into the right Zeeman frequency was the tricky bit once they were fixed enough to lock. You could be off by a small, but stable amount of error if you're locked into the wrong one. If you want to be absolutely sure, zero beat the signal against WWV at 5 or 10 Mhz.
Subsequent versions of the clock had a revision to the tube which used both beams after they were split by the magnet in a clever arrangement to have multiple parallel beams traversing the tube to have an even finer frequency resolution. I was amazed at how narrow the bandpass is relative to 5mhz of the whole thing. No wonder it takes so long to stabilize.
Rubidium standards are fun too, measuring the 1% dip in transmission of light... something the human eye could never notice.
Let me guess... I'll bet you are a Febo Time Nut too! ;)
@DandyDon Nope... I check the time by looking at my non-smart cell phone. I can fix almost anything, which now includes atomic clocks... but I'm content to let the government keep track of the time for me.
@Mike Warot I got one too. An old 5061A. Shame it doesn't work though. I used to be an Instrument tech for HP back in the day. Wouldn't mind talking about how you fixed yours. Glenn
Yes I've been trying to get my hands on one of the Rb Oscillators from a cell phone repeater or tower. It's literaly 3 orders more precise than i need but hey why not if i can find one at a fire sale price.
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. 👍
@Acme Fixer 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.
@John DoDo Doe 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 <1E-15, not 1E-11. It uses three PTB-designed clocks for short term precision, which are adjusted by the national standard consisting of two laser-cooled cesium-fountain clocks.
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.
@Dave Mayes Same here. I tend to think of two eras: real HP and fake HP
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.
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.
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 YouTube. 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.
I can't upvote this enough. Thank you for the clear and concise explanation!
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.
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
Fascinating video. That's the first explanation of a caesium clock I've ever seen that I fully understood from beginning to end.
At 14:30 it seems like the people who built this were developing a finely tuned musical instrument; the inner workings of this clock and an analog synthesizer (like the famous one invented by Robert Moog) start sounding an very much alike... frequency modulation, multiple feedback loops, band pass filters, it's all there!
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.
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.
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.
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.
{^_^}
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.
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.
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.)
I am astonished by the sheer amount of cool toys you guys get to play with! Good work!
Really cool to watch retro HP stuff come to life. Newer ones use grating stabilized laser diodes about the same power of that in a cheap laser printer to pump cesium or rubidium vapor and have a MTTF at over 100k hours. Everything else works tge same except the microwave bits are all solid state. Locks within seconds of reaching the proper vapor cell temperature. 🤓
What a fantastic video Marc! Excellent discussion and explanation of this type of clock
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.
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.
Thank you for this amazing video. You are very good at explaining things!
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 :)
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).
I wonder, as a cool project, could a Cesium clock be used (with some processing) to generate a signal that can replace the oscillator in a cheap digital clock to see if it can be made more accurate (not be 1 minute off after a week of use).
I built a digital clock driven from my rubidium oscillator. It keeps proper time within a few dozen milliseconds per year.
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.
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!
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 !!!
Beautiful video. I have watched it whole and I rarely do that with other videos. Especially the ones involving quantum physics.
Love the hyperfine transition discussion. So fun. Thank you.
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.
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.
This is great. Looking forward to the expansion of the finer concepts
Deserve more views on this channel. Always quality videos that are decent to digest even for [redacted] like me.
Sublimely awesome. These units must be hard to come by.
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.
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.
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.
Beautifully explained, thanks!
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.
Thank you, no really, thank you for showing us this your channel is now officially my favourite channel <3
Really great content !
The build quality of old HP Gear is really outstanding.
Some Versions had a Patek Phillipe dial at the front, was this an Option ?
Yes to both. The optional clock face was indeed a Patek Phillipe originally. Then they made a digital display version, also optional, much less skookum.
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.
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.
Eduardo Artigas - 2020-03-20
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.
Upcycle Electronics - 2020-03-20
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...
How Does it Really Work - 2020-03-20
@Upcycle Electronics 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.
Upcycle Electronics - 2020-03-21
@How Does it Really Work
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 :-)
How Does it Really Work - 2020-03-21
@Upcycle Electronics 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.