Fixed vs Adjustable frequency Rubidium oscillator. - Page 1
Forum section: electronics / general

author: tkamiya
author_rank: Super Contributor
timestamp: June 25, 2020, 05:48:01 am
content: It is my understanding that there are two kind of Rubidium Oscillator:1) 10 MHz OCXO is phase locked through division to Rubidium that is locked. Output is derived directly from 10MHz (for example) These types are of fixed frequency output.2) OCXO is phase locked through division to Rubidium, but OCXO is at frequency other than 10MHz. Frequency needed are synthesized through DDS.Advantage of 1 is low phase noise.Disadvantage of 1 is that output frequency is fixed.Advantage of 2 is output frequency is adjustable.Disadvantage of 2 is relatively high phase noise owing to ultimate frequency being result of DDS.My understanding is PRS10, FRS, LPRO, LPRO101 are type 1On the other hand, FA5650, and FA5680 are type 2. I know there are few more.I am hard time understanding the merit of type 2. High phase noise is basically a very fast frequency instability. When one Chooses rubidium, goal is high stability.I even have a fixed frequency 10MHz frequency standard made with FA-5650A. Why is this?To use as a lab standard, is this sufficient??

author: ArthurDent
author_rank: Super Contributor
timestamp: June 25, 2020, 02:42:42 pm
content: When you say ‘fixed frequency’ you apparently referring to an output of only 10 Mhz, not that the output frequency is fixed, i.e., not adjustable. All Rb standards have to be able to adjust the servo loop to trim the VCO used to generate the frequency output. The Rb cell acts as a narrow band filter to control a voltage controlled oscillator of some sort.You could still use an Rb oscillator that outputs 10 Mhz and feed that to a DDS circuit to get whatever frequency you want. Bottom line is what are you using the output for? If you need some frequency other than 10 Mhz you are probably going to have to live with DDS at some point in the frequency generating string and you can decide whether to get a Rb unit with the DDS built in; or use a 10 Mhz Rb unit and build the DDS circuitry yourself.

author: tkamiya
author_rank: Super Contributor
timestamp: June 25, 2020, 04:28:17 pm
content: No, I mean fixed at a given frequency and I know VCO or VXO is always involved.I've only seen fixed frequency one at 5MHz, 10MHz, 15MHz, 20MHz, and 100MHz. That's understandable, as some lab may require 5MHz standard. If someone is working with optical network, much higher one may be preferred. They are designed for one frequency OUTPUT only.I understand, for very special applications, flexible/adjustable ones would be handy. But still, increased amount of jitter is involved. But as a lab standard, what is the benefit? As I said, I have a commercially made frequency standard for 10MHz that includes variable frequency type SET at 10MHz. Since this is a lab standard, it was likely designed to synchronize equipment. Why would someone choose this verses native 10MHz fixed type?

author: David Hess
author_rank: Super Contributor
timestamp: June 25, 2020, 05:39:56 pm
content: Obviously they would chose a variable frequency output if a fixed output was not available in the frequency they needed.And most equipment which can operate off of an external reference phase locks a low phase noise internal reference to the external reference anyway. All of my timer/counters do this.GPS receivers also do what you describe. Most use an internal DDS driven by a fixed frequency reference to generate timing signals which results in timing jitter but a very few lock their internal frequency reference to GPS producing jitter free timing data.

author: tkamiya
author_rank: Super Contributor
timestamp: June 25, 2020, 09:49:05 pm
content: I've only seen few circuits but the ones I saw (counters), it was detecting a presence of signal at external reference input, and if there is one, switch over to that signal. There were no attempt at phase locking internal ones. At least in my lab, external lab standards are much more accurate than internal ones; although, they may have more jitters.What counters have you seen that does locking internal by external thing?? I once wondered about this, too...

author: syau
author_rank: Frequent Contributor
timestamp: June 25, 2020, 10:53:51 pm
content: Quote from: tkamiya on June 25, 2020, 09:49:05 pmStanford Research SR620

author: tkamiya
author_rank: Super Contributor
timestamp: June 25, 2020, 11:04:00 pm
content: That's a top-of-the-line counter. For that kind of money, I'd expect it to make toast if I set parameters right.Kidding aside, that's a counter that has resolution of 20ps. I'd expect they go extra mile to eliminate all possibilities of instability. I want one!

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: June 26, 2020, 04:34:19 am
content: The main advantage of what you call a type 2 is driven mainly by cost and also by size. With the VCXO oscillator of say 50.255XX MHz directly driving the SRD in the cell you eliminate the multiplier stages that would have been required to get the 5 or 10MHz OCXO up to say 60Mhz. since the VCXO frequency is high enough to drive the DDS directly you get an elegant system with minimal parts count that can be stuffed into a smaller package. Either type as a lab standard can have comparable Allan Deviation performance and short term frequency stability, and if locked to GPS the long term stability is good too!Cheers,Corby

author: tkamiya
author_rank: Super Contributor
timestamp: June 27, 2020, 02:24:42 am
content: Corby,Having your opinion means a lot to me. Thank you very much for responding.Currently, I don't posses an ability to measure phase noise. Getting a decent and consistent Adev has been a constant (and illusive) challenge as well. I have put them on hold as I was starting to obsess on it.I often hear, the type 2, as I call it, has a larger phase noise that uses such as multiplying 10MHz to 10GHz, they are unsuitable. Yet, you say it is usable as a lab standard. In my lab, I have equipment such as 2GHz signal oscillator, 26GHz S/A, and various counters INCLUDING HP53132A, and 5370B. HP5370B, as you know has 20pS resolution in time interval resolution. Would type 2 (as I call it) be suitable for reference in such cases? I'm sure signal generators and S/A would be fine, as they won't be multiplying. But 5370 concerns me as it is capable of such a fine interval measurement.Could you help me understand the limitation of type 2 rubidium oscillators? (I don't know what else to call it!) Compare to GPSDO, that also have quite a short term noise, how bad are they really? Is my concern warranted or overblown?Thank you.

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: June 27, 2020, 04:13:12 am
content: Well the short answer is "I don't know"!I think this might be a good experiment to try.Setup your 5370B and feed it a stable signal while using its internal reference.Then try the 1 and 2 type Rubidium as the reference and see if the counts show any difference.For some applications I know from experience that for short sampling times (below 10 Sec.) a good Quartz like a 10811-60109 will give the best results (a 5061A/B or 5065A with the 10811 retrofit in open loop). Above 10 Sec. I'd use my 5065A (in operate mode).The PR10 and LPRO are I believe what you would call type 1 and both give good performance.www.ke5fx.comhas some nice noise and stability comparisons between the various Rubidium units!Cheers,Corby

author: tkamiya
author_rank: Super Contributor
timestamp: June 27, 2020, 09:22:13 am
content: Corby,There lays the problem. I have a lot of "standards", but I have no idea how stable they are. I have been trying to measure Adev of them well over a year by now but have yet to achieve a reliable result. Their must be a systemic problem somewhere in my system. tvb has been trying to help me identify it. Bob has been coaching me on them. I started obsessing on it, so I had to put that project on hold.I have a box made with 05071-60219 that came out of HP5071A, and I have 10811-60109 (I believe) in HP105B. They work. That's all I can say about them. All of my standards are second-hand purchase and none of them has been accurately characterized. They are quite old as well, so I have no reason to believe their performance is reflective of the original specifications. I literally have a rack full of OCXO to GPSDO, to Rb to Cs. Except for Hydrogen Maser, I have everything. Yet I can trust none.If I can have JUST ONE trust worthy and well characterized standard, my life will be a lot easier. It's like trying to measure the size of ants by rubber ruler.

author: tkamiya
author_rank: Super Contributor
timestamp: June 27, 2020, 11:44:01 pm
content: Just wanted to thank everyone for their contribution and education!

author: David Hess
author_rank: Super Contributor
timestamp: June 28, 2020, 12:15:17 am
content: Quote from: tkamiya on June 25, 2020, 09:49:05 pmMy Racal-Dana 1992 does.

author: JohnPi
author_rank: Regular Contributor
timestamp: June 28, 2020, 05:35:32 pm
content: And th HP53132A, 53131A can be set to automatically switch to an external 10 MHz.

author: tkamiya
author_rank: Super Contributor
timestamp: June 28, 2020, 06:02:05 pm
content: That, I knew.... I have two HP53132A.What's odd is, in auto select reference mode, it will switch from internal to external. But never external to internal. There must be a reason for it but I find that annoying.

author: retrolefty
author_rank: Super Contributor
timestamp: June 28, 2020, 08:14:16 pm
content: Quote from: tkamiya on June 27, 2020, 09:22:13 amAs it's been said, person with one watch always knows the time, person with two (or many) never quite sure.

author: tkamiya
author_rank: Super Contributor
timestamp: June 28, 2020, 10:53:46 pm
content: However, a person with just one watch never will know when it's entirely off! So there!!As a junior time nuts, I'm tired of hearing the line.I collect physical watches, including 120 year old kind, too. That one stays within a second a day. A mechanical 120 year old watch!

author: ArthurDent
author_rank: Super Contributor
timestamp: June 29, 2020, 12:07:05 pm
content: Quote from: tkamiya on June 28, 2020, 10:53:46 pmI just like the complexity and detail inside some watches that the average person would never see.

author: tkamiya
author_rank: Super Contributor
timestamp: June 29, 2020, 12:50:05 pm
content: That's a beautiful Ulysse Nardin! I wasn't aware it made pocket watches. Can I see the dial?I like unique and odd watches. I had some usual, famous, and popular brands but I didn't have that much attraction to them once I had them. So I sold those and bought a bit of test gear.... My current favorite is Corum Bubble and the aforementioned railroad watch. I am somewhat sad that USA used to make such a fine piece of watches and marble of ingenuity, and none of that is left now.I have a local watch maker taking care of my pieces. After a over-haul, the railroad watch keeps +/- 1 sec a day. I mentioned it to him, and he smiled and said, "I hate it when that happened". We had a good laugh.

author: notfaded1
author_rank: Frequent Contributor
timestamp: June 29, 2020, 06:49:21 pm
content: Man Corby your super 5065A with the 10811 retrofit in open loop with the filter... if only these units were around any more! You scored some really good hardware that just isn't around anymore! If you ever want to sell anything let me know please.Bill

author: ArthurDent
author_rank: Super Contributor
timestamp: June 29, 2020, 10:24:57 pm
content: tkamiya - "That's a beautiful Ulysse Nardin! I wasn't aware it made pocket watches. Can I see the dial?"This Ulysse Nardin has a plain navy gun metal case and is a combined chronograph/pocket watch which accounts for the complexity of the movement. I got it about 50 years ago after the previous owner had dropped it and it stopped working. He was going to chuck it in the trash but I said I'd take it if they were going to throw it out and he just gave it to me! Here is a photo of the face plus a couple of other watches, including a low end USSR commemorative watch that works okay.

author: kbrill
author_rank: Contributor
timestamp: July 08, 2020, 07:28:50 pm
content: tkamiya:While of no great importance Efratom FRK series were not uncommonly made for 3.579 MHz NTSC & 4.433 MHz Pal frequencies . I briefly owned an NTSC version packaged in a utilitarian oversized enclosure and on more than one occasion declined to purchase others .Ken

author: tkamiya
author_rank: Super Contributor
timestamp: July 10, 2020, 04:06:17 am
content: ArthurDent:Are you going to get your watch fixed? I have a local watch maker who can do that sort of things.Kbrill:I'd love to hear more about your story. What went wrong?

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: January 15, 2021, 12:19:01 pm
content: Quote from: David Hess on June 25, 2020, 05:39:56 pmAs does my own much modified "Toy" FY6600-60M AWG with its CQE 10MHz OCXO (plus 3N502 clock multiplier) inspired by Arthur Dent's own OCXO upgrade postings into the FY6600 topic thread.Arthur had chosen a simple mechanical switching of external/internal references but concerns (possibly unfounded) that the inevitable glitches this would introduce onto the FPGA 's 50MHz clock input might cause lock ups, led me to use the external 10MHz reference to injection lock the internal 10MHz OCXO to avoid the possibility of such lock ups (glitchless, smooth transitions to and from the external reference).I'd totally missed the even better PLL solution in my researching frequency injection locking solutions untilafterI'd successfully implemented my own frequency injecting moduleThe only reason I've not re-implemented the external reference input module as a PLL controller is simply because the injection circuit works so well and ICBA to rip it out and start overBoth methods have the distinction of automating the change-over and eliminate an unnecessary mechanical change-over switch. When the existing internal reference is already a high quality low phase noise oscillator (in this case, the original cheap 'n' nasty SMD 50MHz XO most certainly wasn't!), injection or phase locking it to an external low phase noise atomic standard (GPSDO or RFS) is the obvious "no-brainer" solution - surely all such test gear with an external reference socket implements a PLL or injection locking methodology?The FE5680A based diy project videos that pollute YouTube have just the same long term frequency stability as the Efratom LPRO 101 units but their choice of DDS to generate the required locked to the XO reference hyperfine transition frequency of the rubidium vapour cell does introduce unwanted spurs and jitter on the XO output making it unsuited for use directly as a reference for use by GHz rated transverters unlike that of the LPRO101's 10MHz output. However, the use of a "Clean up" VC(OC)XO phase locked to the FE5680A's 10MHz output neatly solves that issue.The complicated, DDS free, method used by the Efratom design to generate the hyperfine rubidium transition frequency from a 20MHz VTXO doesn't allow an exact frequency match, requiring a tiny 'bending' of the rubidium vapour cell's frequency output via the C field control which is a necessary 'evil' to fine tune all of these secondary atomic standards regardless of their design.Even though in principle the FE5680A could eliminate such fine tuning, courtesy of the DDS technology, they still require the use of the C field for fine tuning the rubidium hyperfine transition frequency - rubidium vapour lamps and cells are at the mercy of the buffer gasses used and their behaviour in regard of temperature and pressure, making them 'secondary standards' in more ways than just the obvious one of not being caesium upon which the SI second unit of time is based upon.As for generating frequencies other than the 10MHz output from a RFS, the obvious solution is to use a good quality DDS based AWG or RF generator equipped with an external 10MHz reference input socket to phase lock their on-board low phase noise VC(OC)XO to, which permits even the direct use of an FE5680A, spurs and all.I'm currently in the middle of my own Efratom LPRO101 based RFS project (namely housing it in an instrument case sized enclosure to allow me to tightly control its baseplate temperature (and, ultimately add barometric pressure compensation) using a PWM controlled air re-circulation fan (unventilated enclosure design). I've been on yet another quest for best practical methods on PWM fan speed control which has proved, as with so many previous internet research efforts, to be more like (to mix metaphors) a hunt to pull hens' teeth from out of the jaws of Unicorns. As for the question of RFS baseplate temperature control, forget it! There's absolutely fuck all to be found onthatsubject!Anyway, discovering this topic thread was simply the side effect of my internet search for ideas and enlightenment on how to achieve the best possible stability from my RFS project. You have the staggering lack of interest on the part of DIYers building their own rubidium lab frequency references from used surplus RFS kit to the best possible standard over and above simply acquiring one to plonk into a case and sit on a handy shelf in their workshop/lab to thank (or curse) for my presence here.John

author: HB9EVI
author_rank: Frequent Contributor
timestamp: January 15, 2021, 01:12:57 pm
content: Like already reported, the FA-5650A is a noisy devices; first reports about its uselessness for microwave applications date back to about 2010 from KA7OEI, to my memory he also shows a way how to clean up the signal with a rubidium locked oscillator

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: January 16, 2021, 12:57:30 pm
content: Quote from: HB9EVI on January 15, 2021, 01:12:57 pmInteresting, initially I'd thought the "FA-5650A" was a typo for the "FE-5680A" but when I googled " FA-5650A" to check, the only results led to a few hits for the FE-5680A and this topic thread. However, googling for FE-5680A led me to results for both model numbers with one of the results being this informative page :-https://prc68.com/I/FEIFS.shtml.Both models use the same DDS method so need the use a 'clean up' VCXO solution to allow them to be used as 10MHz reference frequency sources for GHz rated transverters (the Efratom LPRO-101 and its variants can be used directly without the need for a 'clean up' add on VCXO).Personally speaking, the Efratom LPROs are a safer purchasing choice imo since you can never be certain which of the '57 varieties' of the FEI models you might actually land up getting lumbered with (the issue of remaining lamp life and whether you get a working unit applies to all of these used RFS models regardless of make and model).The bonus features of 1PPS and, where enabled, programmable frequency setting via a serial interface, are rather overrated imho since the 1PPS has no fixed relationship to the GPS PPS time reference pulse anyway and it makes very little sense to use the RFS directly as a variable (and limited range) frequency source when it's far better to simply employ it as a fixed 10MHz reference for test and measurement kit and use a separate RF generator or AWG to generate a much less limited range of frequencies locked to your 'Atomic reference'.The Efratom LPRO models are more or less a "Straight out of the box" 10MHz secondary atomic reference solution whereas the FEI models might involve some modification or reprogramming to achieve this happy state. If you're prepared to add a clean up oscillator, you can phase lock this to whatever oddball frequency your unit happens to produce if it turns out not be a 10MHz unit, thus neatly avoiding having to open it up to modify it internally for 10MHz.Adding a clean up oscillator to an FA-5650A or FE-5680A is a relatively trivial task in the grand scheme of things so, as long as any of these can produce a stable frequency, locked to the Rubidium physics package whatever oddball frequency they happen to output (8.333333MHz or 15 or 20 MHz for example), phase locking the cleanup oscillator will provide an effective solution without any need to delve into its innards to effect a possibly risky modification.If you're prepared to do the extra work of adding a clean up oscillator (a decent quality VCXO will suffice - no need to go to the expense of a VCOCXO in this case), you can turn this to your advantage to build a cost effective RFS using one of the cheaper less desirable frequency variants of the FE-5680A or else just pay the premium for an Efratom LPRO-101 for an 'easy life' and have done with it.Having said that ("and have done with it"), if you're serious about the ultimate stability, there's a little more work involved than just shoehorning it into a barely large enough plastic or metal case (whether sealed or ventilated) as demonstrated in some of those idiotic youtube videos I've had the displeasure of watching.When you're chasing down stabilities of the order of 10ppt or less (as I am in my quest to quantify the ionospheric errors that plague the single frequency timing GPS based GPSDO models with phase shifts on the order of 5 to 6ns pk-pk that I've observed so far with my modern re-spin of the famously high performance James Miller design using a uBlox M8T in place of the ancient Jupiter-T GPS receiver module used in the original design), you need to hold the base-plate temperature to a very tight tolerance against room temperature variation to achieve the required stability.In my case, that means installing it into a roomy steel instrument case, mounting it onto a quarter inch thick aluminium heat spreader with a large (80mm square by 25mm deep fan cooled) CPU heatsink bolted onto it to control heat transfer rate to the walls via recirculation inside of this unvented case using PWM fan speed control mediated by a bead thermistor literally embedded into the centre of said heat spreader.Initial testing of the effectiveness of this recirculating fan cooling system in an unvented steel enclosure of 1800 sq cm total panel area indicates this is a viable way to control the base-plate temperature with the absolute minimum of openings for a bi-colour front panel led with two on the rear panel for a 5.5mm DC jack and an SMA-F output socket.Although the 'recommended' DC supply voltage is quoted as "24 volts", the full voltage range is given as from 19 to 32 volts (with power consumption test figures curiously covering the slightly wider range of 18 to 36 volts). After initially testing with a 24v supply (just under 2 minutes to lock), I elected to use a 19v laptop charging brick (I have at least three suitable laptop chargers to hand) which extended the time to lock to a pretty consistent 192 seconds from a room temperature in the range 20 to 25 deg C. The reduction in energy consumption after lock up is only a modest 1W in this case but 'Every little helps'as does keeping the PSU outside of the case (improved charging brick reliability due to lower temperature operation and faster swap out of any failed units being two other obvious benefits as well as simplifying some form of battery backup I might wish to add at a later date).My initial idea for fan speed control had been simply to turn it on and off to control the base-plate temperature since there is a rather massive thermal inertia involved. However, my solderless breadboard lash up had introduced an accidental PWM effect around the switching point (as such solderless breadboard lashups are wont to do) and the 12mV hysteresis on the temperature sensor signal disappeared, leaving it being held to a steady reading once the temperature had stabilised which inspired me to use PWM 'on purpose' as opposed to 'by accident'. I'm now at the stage of testing my PWM circuit ideas, having finally extracted those hens' teeth from out of the jaws of all those Unicorns googling efforts.I'm aiming for a base-plate temperature of 35 deg C which should be good for a maximum room temperature of 27 to 28 degrees or so (here, in this part of the UK, it's very rare to see summertime room temperatures go above 25 to 27 degrees). I'd prefer to avoid going to a higher base-plate temperature but, if needs must, I still have the option to drill some discreet ventilation holes to enable some external cooling airflow to avoid raising the set temperature above my 35 deg target.Unfortunately, I won't be able to verify the actual cooling requirements until I have everything mounted inside and the enclosure sealed up ready for final testing but I do at least have a contingency plan in place should a more effective cooling solution ultimately prove to be required.If anyone is curious about why I am going to so much trouble in using a recirculation cooling solution in a sealed case rather than 'take the easy way out' with a ventilated cooling setup, it's because this, if it works as well as my initial tests indicate, is actually the most pragmatic approach in that, as well as minimising EMI leakage paths with additional routes for ingress and egress of electrical interference, I'm also avoiding unnecessary work on modifying the case as well as maximising the possibility of repurposing it should I later decide to rehouse my RFS in a better enclosure.I hate unnecessary work and needless mutilation of an otherwise serviceable enclosure that could be used in a later project should it ever become redundant to the current project - I like to keep my options as wide open as much as I possibly can.John

author: HB9EVI
author_rank: Frequent Contributor
timestamp: January 16, 2021, 02:08:36 pm
content: Indeed I meant the FE-5680A, since it's the one I own, so investigated about that one in the pre-GPSDO timesCertainly the Efratom LPRO are a much better choice, but from that what I see both types are rather expensive now; I got my one for about 50$ in 2011

author: Johnny B Good
author_rank: Frequent Contributor
timestamp: January 16, 2021, 08:41:03 pm
content: I bought mine from a US based Ebay seller (EEVBlog member testpoint1) for $179 plus another 70 dollars for postage and import duty charges in August last year. As per usual, it's a case of "Market Forces" at work, "Supply and Demand", and those halcyon days of the 50 dollar rubidium oscillator are now long since gone.John

author: martinr33
author_rank: Frequent Contributor
timestamp: January 17, 2021, 03:08:24 am
content: I'm only working with cheap stuff, seems that I like to fix the cheap rubidium oscisllators on eBay... and 53132as... and...However, I have put together:- A couple of 53132as with high-grade crystal oscillator boards (units can source or use a 10MHz reference signal)- A GPS frequency generator based on a Trimble module (eBay)- An HP 33120A waveform generator with the external lock for an external oscillatorWhat I see is:- The two 53132As running on their internal enhanced clocks track each other precisely over short periods.- The GPS oscillator output varies by maybe 100 counts on the 12 digit scale- The rubidium oscillators hold close to frequency over long periods, once they have locked in- it takes a little while after they lock in to reach final frequencyGPS is my only trustworthy reference, but the deviation around 10MHz makes it tricky as a calibration source.So.. is there a GPS-based oscillator that does not deliver a wandering 10MHz? (we're talking parts per trillion here).

author: Wim13
author_rank: Frequent Contributor
timestamp: January 17, 2021, 03:07:54 pm
content: So.. is there a GPS-based oscillator that does not deliver a wandering 10MHz? (we're talking parts per trillion here).??Yes there are, GPS standaards see attachment , 1xE-12But i use two rubidium clocks and two GPSDO, and a HP5370, and most important excel spreadsheet,then i can get close to 1xE-11

author: martinr33
author_rank: Frequent Contributor
timestamp: January 17, 2021, 06:08:55 pm
content: You can see in the spec that the short term variation in the GPS signal shows up in the output.I'm assuming that the best crystals can deliver 1e-12 stability in the short term (I see this on Oscilloquartz, Morion and Trimble double oven devices when I run two counters on the same input).So why don't the standards use the GPS to discipline a local oscillator in the short term?Maybe because the specified performance on the oscillator is not good enough?

author: Wim13
author_rank: Frequent Contributor
timestamp: January 17, 2021, 07:15:20 pm
content: The problem with GPS signals on short term, you have to deal with radio paths that are not stable,so your GPS reference is always moving.a path difference of 1 meter is already 3 nSec away.The sats are moving, the ionsfeer is moving, reflections, and so on, the software must be able tocorrect this all on the short term, is not easy.I have also an old Jupiter GPS, that is still working, (telling me it is 2001, wrong week number),but works for positioning and time pulse oke, on a scoop you can see on these early models that on the short it is moving 50 to 100 nSec per sec.The manual specs of these old model is even worse, 1 uSec per sec .

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: January 18, 2021, 01:08:28 am
content: martinr33,Pick one of your Rubidium units, run it 24/7, and track the long term phase against your GPS.Over a few days of trimming the Rubidium you will have a "trustworthy reference".Then you can calibrate to reasonable levels in a much shorted period of time.Of course picking up a Cesium unit with some life in the tube would be ideal!Cheers,Corby

author: martinr33
author_rank: Frequent Contributor
timestamp: January 18, 2021, 04:33:31 am
content: Thanks, Corby -- I use the precision double oven oscillators in my two counters as my references.- I tune them with a GPSDO. When they are measuring the GPSDO at 10MHz over a longer period, I figure that they are set. That takes a few tries, as I can't control the calibration timing in the 53132as. I have ot hit the GPSDO just right.- Then I use that to set the rubidiums. I have FEI units, which have a remakably diverse number of ways to set the frequency across the range of units, and in some cases a very annoying connector.