The drift you see is normal because the rubidium oscillator is not locked to any common reference.. Actually, the drift should be more prominent on your GPS disciplined oscillator. To observe the accuracy of the rubidim clock you shoud make it also GPS disciplined as you planned, and then compare both disciplined oscillators (OCXO and rubudium) between update periods from the satelllite and that will tell you which one drifts more, and should confirm the the rubudium one has less drift.

I used these in a positioning system called Starfix. Starfix was a positioning (navigation) system that was designed for providing precise positioning information for offshore work in the Gulf of Mexico. It was similar to a differential GPS system but we used geosynchronous satellites and put up our own spread spectrum signal. GPS was not available at the time. As I remember we built 62 systems. They were great little oscillators, very low phase noise. I still have an Efratom FRT in my lab that has been running since 1987.

Amazing video. I see I am not alone in the "one man with two watches never know the exact time" thing. Can't wait for part 2 !!!

6:50 A-ha! That was on my mind since the beginning of the video - a useful bit of information there, saving us the trouble of finding out ourselves. I guess that makes buying a second hand one a gamble then.

Great video. Hope the wait for part two isn’t long

A 50 terminator will definitely help clean up your waveform. My eBay FRS (an even older model) was pretty funky running straight in to the high impedance input of the Oscope. With the termination it was perfect. BTW, back in the '70s I used to work with the HP Cesium standard as shown in the video and have used various Cesium and Rubidium standards over the years.

lmao, loved the pokemon lilycove "elevator music" thrown in!

For anyone curious, I did a quick calculation of the frequency difference between the GPSDO and the Rb oscillator. Using the information from www.microfarad.de/blog/comparing-frequencies-with-an-oscilloscope/, I found that at 9:40 the Rb 10 MHz was scrolling at about 1 period every 1m8s, which works out to a difference of about 14 mHz or 1.4 ppb at 10 MHz. I'd say that's pretty damn close!

Waiting.....waiting....waiting For part 2.

That's a great deal for the efratom part, well explained.

The external trim is there to take care of the last few decimals of error. A stable voltage there, whether from a GPS disciplined servo, or just days of manual adjustment, should get you to (or near) the rated accuracy. You may need to do some tweaking of the servo coefficients on the GPSDO board to better suit the stability characteristics of the Rb relative to Quartz oven.

I repaired some rubidium oscillators in the 80s. They were pretty accurate. (10E-11 if memory serves) We compared them to national standard broadcasted during a few hours (they were 10E-12 or -14 at the time. I’m not sure)

Cool vid, hope to see you at a TNG soon!!!

Very nice video, thank you 😊

Just a thought. There should be a C-Field trim to bring the frequency in. The hyperfine transition is influenced by the magnetic field and so the C-field trim compensates for this. That will likely be the external trim voltage you will be using your GPS disciplining board to control.

I've long wanted to build a 10MHz Rubidium frequency standard for my lab, but the formerly plentiful modules from the old GSM stations have turned rather rare by now, and usually go for 250$+, which just isn't worth it for me anymore.

I have a similar rubidium oscillator and that also lost sync from time to time. When I attached a heatsink and addad a blower to keep the case cool, it didn't do that anymore. Just make sure the cooling is not too much or the heater will have a hard time...

Looks like you need a third reference ;) Nice start screen on the scope btw.

Cool video! I played around a lot with Rubidiums back in the day when the FE-5680As were cheap and plentiful on eBay. As you know and mentioned, the more references you have, the less sure you are about which one is right. :) Rbs aren't perfect, with good enough equipment you can measure the drift and other weirdness that they exhibit, it's just further down in the noise of most people's test equipment. Getting that hooked up to your GPSDO, especially if you put it on a UPS to ride through power outages, should net you really nice long term stability. The OCXO version of your reference might still be useful if it ends up having lower phase noise. I'm looking forward to the follow up!

I don't really "do RF" but I really like your presentation style.

Hello. I have the same model of oscilloscope. It is much better and precise to use 1 and 3 or 2 & 4 channels at the same time. Because of internal architecture of this model of SIGLENT. When you use 1&2 (or 3&4) channels at he same time, ADC works in interlive mode and the real sampling rate is two times lower.

I built a totally digital GPSDO/NTP server around an Rb (Symmetricom X72 or SA.22c - now owned by Microchip, by way of Microsemi) some years back. It did all of the PLL stuff in software, using the Rb's digital frequency adjustment, and it output a whole bunch of stats over the network so you could monitor it in real time. I got the control loop dialed in real nice and it worked great. Ironically, I built it before I became a ham, and disassembled it shortly after becoming a ham, because I'm terrible at hardware design. The thing had RF (10MHz and some other frequencies) flying around all over the place on unshielded wires, and it was in the same room where I was building my HF shack, so I had to kill it to get rid of the interference! For a long time I've wanted to bring it back in a better version without the random mass of wires, but learning PCB design is on my "maybe someday" list.

They're *stable* (once warmed up and locked), and they can be reasonably (extremely) accurate 'out-of-the-box'. But they're not *inherently* exactly 10MHz, just really (really, really...) close. Local effects (e.g. magnetic environment) and shipping might have voided (LOL) any previous calibration. They can be calibrated using the potentiometer input to fine tune some internal magnetic field. And they'd need to be recalibrated in a mandated cycle (e.g. yearly). You calibrate it against the GPSDO, which is (by design) traceable back to government standards. 73

Cool video

You can put a bandpass filter on the 10 MHz output. That would give you a clean sine wave.

Nice video, but I have couple of notes. 1. You really should have a proper heatsink on the RbO base plate. The base plate temperature should be somewhere around 30-38 deg. C (mine is currently operating at 33 deg. C with passive heatsink). 2. Personally, I am not sure that the idea to put RbO inside the GPS loop is a good idea. I am certainly no time/frequency professional or academic, but I had a rather long e-mail discussion with Brooks Shera (the man, who basically invented the idea of GPS pacification of OCXOs back in 1998) in summer 2000 about this aspect. And his opinion was that RbO is much better to be left alone as a free running frequency normal with excellent short term stability and that the "kicking" of RbO with 1PPS can only make things worse, especially if the time constant of FIR filter is not long enough (typically days or weeks). Same thing is valid when it comes to external steering by some component. Either the multi-turn potenciometer or some DAC. The thermal stability of those components is almost always much worse then the thermal stability of the RbO module without any external stimulus. 3. In my home lab, I am using GPS pacified OCXO (an old HP10811A) with Motorola OnCore UT+ (in position fix mode) built according to the Brooks Shera design - www.qsl.net/n9zia/wireless/QST_GPS.pdf for almost 25 years with only one interruption in 2002 (floods in Czech republic) and even today, the precision is really good. But the short time stability is not so good. So, if I want to measure something with better short term stability, I simply switch on my RbO, wait 3-6 hours or better to next day and do measurements. After this, I switch my RbO off until next measurement. RbO is not like OCXO and it does not need to be switched-on without interruption for decades. It will not become better after ten or twenty years, like good red wine or OCXO. :)

Never heard of these before, but anything with an ‘ium’ at the end of its name (apart from pentium) tends to pique my interest, so here I am.

what a fascinating video. i have now learned some things. thank you sir. i will hit that subscribe button. hmm my thoughts are that the drift is too much. the rate of rotation of that circle is pretty fast. my thoughts are that a magic cesium clock and gps satellite would not be off by that much. a little bit yeah but not that much

me when my dealer named 'god' gives 1 mega ohm impendance: yess me when 'god' gives me apple 2gs with dead capcitor again: nooooooo

Anything is serviceable just not all companies respect you enough to let you buy parts. If I understand your explanation right it may be possible to replace the IR lamp with something else that can generate the correct light.

CSAC when? 😉

wait til the modular music nerds get ahold of this

Getting some cheap chinese 50 ohm in-line terminators for your scope might be a cheap investment. Will they be flat, capacitance-less response up to 1Ghz? lol no. Will they do the job for 99.9% of cases up to 100Mhz? Yeah. That slow of a lissajous plot for a 20 year old, completely free-running, clock is amazing. Atoms, man.

I think it's 32 years old :P

$50.00 each for 3? Every time I look on eBay for these they are selling for $175.00 for 1. If you are lucky.

$50 bucks... these things going for $150 at least on eBay...