EEVblog #456 - CSIRO Rubidium Frequency Standard - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: April 19, 2013, 12:07:53 am
content: Dave uses his CSIRO National Measurement Institute rubidium frequency standard to calibrate and adjust his Agilent 53131A frequency counter.With bonus teardowns.

author: mswhin63
author_rank: Frequent Contributor
timestamp: April 19, 2013, 12:19:51 am
content: I love those racks, reminds me of the old railway days working on the radio and signalling systems

author: olsenn
author_rank: Frequent Contributor
timestamp: April 19, 2013, 12:40:38 am
content: 0.6ppm is nothing to sneeze at for a standard OTC crystal oscillator. Aging will be greater than that for a single year, so don't get too fond of that accuracy... that's what the Rb Std. is for. Speaking of which, do you still have your FE-5680A? How about adding one Rb. Std to the 10MHz in of your new counter and seeing that the other is a perfect 10MHz as well?

author: EEVblog
author_rank: Unknown
timestamp: April 19, 2013, 12:49:31 am
content: Quote from: olsenn on April 19, 2013, 12:40:38 amYes, that's the idea of course.The stock oscillators are crap, it'll drift more than the SS MinnowQuoteYou won't see any difference with 10 digits

author: free_electron
author_rank: Super Contributor
timestamp: April 19, 2013, 02:01:46 am
content: The reason for the delta supply is because of the oven and the other options.This supply is always running and the switch on the front only powers the counter section. If the oven is installed it is kept hot.The little board with the transformer is an AC power supply for the filament of the VFD. the filament needs AC voltage to prevent VFD burning. as the delta switcher only delivers DC they need this little inverter.now, since you got the rubidium standard just feed the 10MHz from the Rubidium standard into the back of the counter 'EXT REF IN' bnc and tell the counter to use the external reference. now your counter will always be spot on.hoop the rubidium standard up to an UPS and you are golden !

author: lowimpedance
author_rank: Super Contributor
timestamp: April 19, 2013, 03:32:07 am
content: If you want to see what the NMI actually use for there time standards check out the link below.http://www.measurement.gov.au/Services/calibrationtesting/Pages/TimeandFrequencyFacilities.aspx

author: tylerl
author_rank: Contributor
timestamp: April 19, 2013, 05:03:01 am
content: According to themanual for the 53131A, you can connect your rubidium frequency standard up to the back of the frequency counter (search the PDF for the words "external timebase"), and suddenly the accuracy of your Agilent frequency counter should improve pretty noticeably.So then why try to calibrate the 53131A using the trim pot?

author: EEVblog
author_rank: Unknown
timestamp: April 19, 2013, 05:08:30 am
content: Quote from: tylerl on April 19, 2013, 05:03:01 amWhy? Because I could.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: April 19, 2013, 05:17:54 am
content: Hello AllWhen dave did the tour of the HP cal lab and looked at the cesium clock it was stated that the cesium source eventually wears out or is consumed as the atoms are boiled off. Do rubidium clocks suffer the same type of life-span limit? If no, how do they die? Those FE-5680 units can look thoroughly knackered from external appearance.

author: ddavidebor
author_rank: Super Contributor
timestamp: April 19, 2013, 05:24:17 am
content: Quote from: EEVblog on April 19, 2013, 12:49:31 amYou need to use a scope and measure with the watch the time the two signal need for drift of X degreeAnd make some calculation, don't know what calculation

author: Bored@Work
author_rank: Super Contributor
timestamp: April 19, 2013, 06:05:52 am
content: Quote from: chickenHeadKnob on April 19, 2013, 05:17:54 amYes, the rubidium tube or lamp wears out. Manufacturers specify a lifetime. Something like ten years is typical. It does not mean they immediately die after ten years, but the likehood of them dying starts to get significantly higher. One reason you see so many used rubidium oscillators on eBay and other sites it exactly this. Gear gets decommissioned because the rubidium oscillator is near its expected lifetime. (another reason is rubidium oscillators are used in mobile phone network gear in larger amounts, and phone companies constantly update and upgrade their mobile phone networks, throwing out older gear).

author: Huluvu
author_rank: Regular Contributor
timestamp: April 19, 2013, 06:12:57 am
content: Quote from: free_electron on April 19, 2013, 02:01:46 am@Dave can you please look at the Delta PSU board for some PN (maybe I can check in SAP ......)

author: EEVblog
author_rank: Unknown
timestamp: April 19, 2013, 06:35:37 am
content: Quote from: chickenHeadKnob on April 19, 2013, 05:17:54 amYes, the Stanford unit specifies a guaranteed 20 year life.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: April 19, 2013, 09:03:04 am
content: Quote from: EEVblog on April 19, 2013, 12:49:31 am

author: grumpydoc
author_rank: Super Contributor
timestamp: April 19, 2013, 12:27:13 pm
content: QuoteThey're also quite difficult to adjust with any precision as Dave discovered - especially if there is any slack in the trimmer. Also, sometimes, any change can perturb the oscillator by orders of magnitude more than the adjustment you're trying to achieve.I'm surprised that the oscillator isn't voltage controlled with a DAC to generate the VFC- that is not only a better way of doing it but lends itself to automatic calibration rather more easily than sticking a screwdriver into a trimmer. Especially as the tongue angle calibration on most units tends to be very poorI suspect that these were intended to be used with the Rubidium standard rather than the inbuilt oscillator.

author: firewalker
author_rank: Super Contributor
timestamp: April 19, 2013, 12:36:44 pm
content: Would it worth the trouble to replace that trim cap with something more "trimable"?Alexander.

author: c4757p
author_rank: Super Contributor
timestamp: April 19, 2013, 12:46:16 pm
content: Quote from: grumpydoc on April 19, 2013, 12:27:13 pmYeah, I don't have too much experience with "professional" equipment like this, but if has an external reference input I wouldn't be expecting much from the internal reference.Of course, my own experience proves my suspicion wrong (my HP function generator with external ref input is 1ppm out from a Rb reference, and it's not even ovenized), so take that with a grain of salt...

author: grumpydoc
author_rank: Super Contributor
timestamp: April 19, 2013, 12:48:08 pm
content: QuoteProbably not - the underlying drift (both temperaature and aging) will be such that you're only ever going to get 6 digits of accuracy from it.There are some micro ovenised units available from the Far East via ebay. I've had a couple of these to replace failed oscilators in couters and sig gens and they're pretty OK and would be a *much* better replacement if you wanted to improve on the standard crystal oscillator - but, then, Dave has multiple Rubidium units to use now

author: EEVblog
author_rank: Unknown
timestamp: April 19, 2013, 12:58:41 pm
content: Yes the stock oscillator is just a toy in such a good counter. They expect you to at least spring for the oven osc.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: April 19, 2013, 01:03:52 pm
content: Could you feed one of the rb outputs to a clock input on the counter?

author: EEVblog
author_rank: Unknown
timestamp: April 19, 2013, 01:16:37 pm
content: Quote from: Ed.Kloonk on April 19, 2013, 01:03:52 pmOf course, that's why all counters have external clock inputs.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: April 19, 2013, 01:17:44 pm
content: Quote from: EEVblog on April 19, 2013, 01:16:37 pmBoozy tonite mate sorry.

author: bingo600
author_rank: Super Contributor
timestamp: April 19, 2013, 01:33:52 pm
content: Daummmm .... DaveThis is "cheating" & Not fairDid you get both the RB & Freq Counter for $260A used PRS10 is 750+ US$ on the 'Bay ... aloneSend it to me for "Looooooonnnngggg time" calibration testing ... 10 years or so ...I have the GPS antenna for it/Bingo

author: EEVblog
author_rank: Unknown
timestamp: April 19, 2013, 01:39:35 pm
content: Quote from: bingo600 on April 19, 2013, 01:33:52 pmYep, both, plus the industrial PC, plus the APC PSU and batt.QuoteYes, they are not cheap. I could sell both for a big profit, but the PRS10 is just so darn nice...I had an FS725 once, but sold that.

author: kyndal
author_rank: Regular Contributor
timestamp: April 19, 2013, 02:04:16 pm
content: if i had a GPS disciplined, rubidium frequency standard on handi would do the only right thing for a hacker to do...take my egg timer apart. and replace the 32.768 khz crystal with a divide by 305.17578125... circuitand feed it the 10mhz reference...finally go cook some eggs up with a only a few ppm's worth of precision and consistencychallenge posted!.haha../Kyndal

author: ddavidebor
author_rank: Super Contributor
timestamp: April 19, 2013, 02:12:50 pm
content: I don't understand a thing....Gps provide pps, but is pps used to correct the rubidium or only is a separate thing?And what tipe of equipment use ppm input?

author: ddavidebor
author_rank: Super Contributor
timestamp: April 19, 2013, 02:14:18 pm
content: Oh, i can't understand a word.What you say when you say something like "conformally coted" referring to the board inside the rubidum standard?

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: April 19, 2013, 02:16:57 pm
content: Quote from: ddavidebor on April 19, 2013, 02:14:18 pmThe clear, shiny coating that covers all components on the board.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: April 19, 2013, 02:20:13 pm
content: ddavidebor,When you sayOh, i can't understand a word.orI don't understand a thing....It sounds like you are not understanding anything.Better:I don't understand one particular word, I don't understand something.Hope that helps.

author: bingo600
author_rank: Super Contributor
timestamp: April 19, 2013, 02:21:08 pm
content: Quote from: ddavidebor on April 19, 2013, 02:12:50 pmYes the PRS10 takes an external 1-PPS and can dicipline the 10Mhz rubidium output against the GPS provided 1-PPS.So you get a "selfcalibrating" 10Mhz RB.I have an X72 Rubidium , bought on the 'Bay for that purpose , but it (1-PPS diciplining) was implemented in firmware 5.x.And the 'Bay seller forgot to say my X72 had 4.x firmware in it .... So watch out if trying to get an X72 to do it./Bingo

author: tinhead
author_rank: Super Contributor
timestamp: April 19, 2013, 02:21:52 pm
content: Quote from: ddavidebor on April 19, 2013, 02:14:18 pmhttp://en.wikipedia.org/wiki/Conformal_coating

author: free_electron
author_rank: Super Contributor
timestamp: April 19, 2013, 02:54:52 pm
content: Quote from: grumpydoc on April 19, 2013, 12:27:13 pmThe reason is that there is an option for this machine to have a real oven installed inside. That is why there is so much empty space.These counters use a switching power supply from delta (custom hp part number) that is always on. The power button is a soft power button that only toggles power to the counter section.In the big cavity between front and power supply you can install an 11806 oven oscillator. Those beasts are dead stable. They go on ebay for about 100$ but you need the interface board. (Working on that.. I have a 54131 too and i have an 11806... ) the interface board is a few connectors and two co parators that signal the state of the oven to the counter( temp ok and voltage ok)On the right hand side , above the fromt end (between front and the bix xilinx ) there is the room to install the third channel. Depending on the freque cy band chosen this module either screws onto the right hand support strut , or it is a block that drops in.So there you go. That is why this thing looks so empty and is built the way it is built.The two empty flatcable connectors are to connect the oven and prescaler for channel3.If you have a standard , like daves rubidium, just hook it up to the back panel ref-in. The counter will detect it , disengage from its built in reference and use the incoming signal. There is some monitoring circuitry that detects the signal falling away and then the machine switches back to its own source.There is a reason for using 10Mhz. They are the easiest ovens to make and agilent started , back in the hp dayss, to provide an extra input for 10mhz on all their time related equipment ( scopes, signal gens, spectrum analysers etc...) when you buy an oven for a machine it comes with an extra bnc that brings the ref out.Originally they sold the oven in an external case as well.Every machine has a ref in and ref out and you can daisy-chain the machines. There is a buffer inside each machine. Of course you incurr skew every time you pass through an instrument.That is why they sell distribution amplifiers. These are carefully designed to also be phase aligned outputs. You do need to use cables with identical length though !In my ADSL days i had an agilend gps disciplined reference ( now owned by symmetricom) and such an amplifier. All machinery in the lab was connected to it. We had two network analysers. Prior to connecting them we saw differences between the machines. Connect both to the standard and the became spot on. ( they were calibrated by agilent in their lab using such a standard , so the moment we connected to ours they were performing at their peak.

author: Zad
author_rank: Super Contributor
timestamp: April 19, 2013, 04:01:33 pm
content: Quote from: bingo600 on April 19, 2013, 01:33:52 pmYou are looking in the wrong place then. They have been going recently for $400www.ebay.co.uk/itm/SRS-STANFORD-RESEARCH-SYSTEM-PRS10-RUBIDIUM-FREQUENCY-STANDARD-/130891002337

author: gxti
author_rank: Frequent Contributor
timestamp: April 19, 2013, 05:45:31 pm
content: Quote from: chickenHeadKnob on April 19, 2013, 05:17:54 amCesium oscillators consume cesium as they operate, it's an irreversible process. Rubidiums do not have such a problem. They do deteriorate with age as the rubidium metal deposits on the wall of the chamber but it is possible to 'rejuvenate' it with heat.

author: bingo600
author_rank: Super Contributor
timestamp: April 19, 2013, 09:19:51 pm
content: Quote from: Zad on April 19, 2013, 04:01:33 pmHmmm ... I hope there are more to come ...Thnx/Bingo

author: EV
author_rank: Frequent Contributor
timestamp: April 20, 2013, 09:03:26 am
content: Here is Self made GPS clocks 10 MHz signal as input to Agilent 53131A counter channel 2 (Pic-1) and self made Rubidium standard as input to Agilent 53131A counter Ref input (Pic-2). Measurement result is in Pic-3. Gate time is 60 seconds.

author: jpb
author_rank: Super Contributor
timestamp: April 20, 2013, 09:26:25 am
content: Quote from: kyndal on April 19, 2013, 02:04:16 pmYou'd also need a multiple laser interferometer to get the egg's precise volume and surface area and a very accurate set of scales and measuring the air pressure would also need tobe done to very high precision to determine the boiling point of the water.On the timing side, provided you wanted a whole number of seconds (say precisely 3 1/2 minutes) then the 1ppm from GPS is typically in the 10s of nsecs range,which over 210 secs would be reduced further. This may be good enough.

author: free_electron
author_rank: Super Contributor
timestamp: April 20, 2013, 01:45:03 pm
content: Quote from: jpb on April 20, 2013, 09:26:25 amThat's all easy stuff. It's getting the calibrated chicken that's the hard bit...

author: codeboy2k
author_rank: Super Contributor
timestamp: April 20, 2013, 08:54:27 pm
content: Quote from: free_electron on April 20, 2013, 01:45:03 pmNegative Feedback. Using the aforementioned laser measuring tools, each egg is measured at the factory as its laid. When it's high or low out of spec, the information is fed back to the hen that laid it, via a much higher power laserOnce this loop stabilizes only hens laying eggs in spec will be alive in the hen house

author: c4757p
author_rank: Super Contributor
timestamp: April 20, 2013, 08:55:43 pm
content: Quote from: codeboy2k on April 20, 2013, 08:54:27 pmDammit! I was going to say that.

author: codeboy2k
author_rank: Super Contributor
timestamp: April 20, 2013, 09:03:58 pm
content: Dave,Those are nice in-house designed interface boards for the PRS10 and the GPS receiver. They are not that difficult to design and build and even troubleshoot, but it's nice to (a) have the schematics, and (b) read the schematics of a proven design.Given that your Australian tax dollars funded the development of those boards, I think they should release the schematics for it to you, if they haven't already made them available.

author: hairykiwi
author_rank: Contributor
timestamp: April 20, 2013, 09:14:57 pm
content: Quote from: Zad on April 19, 2013, 04:01:33 pmThanks for sharing Zad. And /Bingo - It looks like they're relisted again.

author: codeboy2k
author_rank: Super Contributor
timestamp: April 20, 2013, 09:51:05 pm
content: Chip scale atomic clock developed at the NIST in the USALots of information there, but the web page is not clear about what can be clicked on. Most of the numbered lists on their pages are actually click-able links, but have nothing to indicate that.http://tf.nist.gov/timefreq/ofm/smallclock/CSAC.html

author: hairykiwi
author_rank: Contributor
timestamp: April 20, 2013, 10:20:50 pm
content: codeboy2k - the specs on that device arereally AWESOME!Though, if it were several orders of magnitude larger, I'd say it definitely looks like it came out of a well used DeLorean.Back toaffordablefrequency standards, it would be really interesting to hear what those of you with a Rubidium Frequency Standard laying around think of the 'Network Frequency Transfer' project. It's advertised as a 'better than 1ppm' frequency standard by it's Danish creator, Kasper / KKP. Here's the link to his public announcement of the project back in 2009:http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=82842&highlight=ntpAccording to one guy on that thread - alank2, it's accuracy is pretty impressive:QuoteAnd here's Kaspers original post for convenience. (His pdf and exe links are still working.)Quote

author: grumpydoc
author_rank: Super Contributor
timestamp: April 20, 2013, 10:33:21 pm
content: Neat.It's certainly better than no reference at all but to be fair 1ppm is only really useful for a straightforward crystal oscillator, or perhaps a TCXO. Good ovened oscillators are stable enough to try to set them up to 1x10-8to 1x10-9, Rubidium units should be in the in the 10-9to 10-11range.

author: EEVblog
author_rank: Unknown
timestamp: April 20, 2013, 10:55:15 pm
content: Quote from: grumpydoc on April 20, 2013, 10:33:21 pmI agree that 1ppm is pretty useless.You can get a lot better than 1ppm by a DIY TXCO design (but it's messy of course).I don't really consider anything a decent reference standard unless it's at least rubidium. e.g. > x10-9Sure you can get some good oven based oscillators, but they just aren't really the same level.

author: codeboy2k
author_rank: Super Contributor
timestamp: April 20, 2013, 11:11:49 pm
content: I don't have a rubidium standard here, but I did buy a couple of old 10Mhz ovens from eBay a few months back.. I'm working on a DIY GPS disciplined 10Mhz standard for my own home lab.After several hours (I think it's 24 to 48 hours) you can get its Allen Variance down to between 10-11or 10-12. Thats still good for my lab. I don't have anything here that can measure that good yet.And I agree, I would rather have a rubidium standard as the reference clock to discipline. The oven clock will drift more and faster than the Rb standard if it loses GPS lock. So for my uses, I am hoping that my ovenized standard will be ok.. I'm thinking about putting a lock LED and a 48HR LED. One light locks when it has GPS lock, the other light locks after 48 hours of consistent lock. Then I'll know when the output has been "in training" long enough to assume it's good (like I said, I can't measure it).

author: olsenn
author_rank: Frequent Contributor
timestamp: April 21, 2013, 12:09:40 am
content: Out of curiosity, has anyone ever tried making a circuit that takes the average frequency of say 10 or 20 standard (pick of the bunch) crystal oscillators to get higher accuracy at low power levels? How about circuits that compensate for the temperature-frequency variation curve?

author: c4757p
author_rank: Super Contributor
timestamp: April 21, 2013, 12:14:29 am
content: Quote from: olsenn on April 21, 2013, 12:09:40 amI'm no statistician, but I don't think this will be worth much. It's entirely possible for all of them to be out in the same direction - and not entirely unlikely.QuoteYou mean aTCXO?

author: olsenn
author_rank: Frequent Contributor
timestamp: April 21, 2013, 12:58:55 am
content: QuotePossibly, but I reckon not probably. Dave did a video on this before using resistors instead of crystals. However, I could be wrong; for all I know, drift could always be in one direction for crystal oscillators.QuoteI was under the impression that TCXO is an oscillator that is either kept at a specific temperature with an oven, or contains housing (or possibly even is a certain cut of crystal) that is insensitive to frequency variations due to temperature. Do these oscillators actually come with active circuitry built in?

author: EEVblog
author_rank: Unknown
timestamp: April 21, 2013, 01:12:21 am
content: Quote from: olsenn on April 21, 2013, 12:58:55 amIt's not, when you skew end point correct the drift it can look something like this (real data I've measured):That graph is at a constant temp in a thermal chamber.Shock and vibration can "reset" the drift characteristic of crystals. I've done experiments on this.QuoteA TCXO is one that has extra (analog) circuitry that tries to correct for the (measured) drift of the crystal against the ambient temperature.A DTCXO (MTCXO) does the same thing, but with a digital lookup table and a microprocessor that adjusts the frequency based on the current ambient temperature. These cost a lot because each one unit has to be individually tested at each frequency point (say 1degC steps) and a reference adjustment figure programmed in for each temp.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: April 21, 2013, 01:42:10 am
content: Quote from: olsenn on April 21, 2013, 12:09:40 amTake a bunch of oscillators - crystals, pendulums, what have you, and then put them in close physical proximity to each other so that they can influence one another. You will find they tend to drift either in phase or completely anti-phase (-180).as this is the lowest 'system' energy state. It is a real fundamental physical effect with many natural examples.have a look at this youtube:http://youtu.be/kqFc4wriBvE

author: max-bit
author_rank: Frequent Contributor
timestamp: April 21, 2013, 08:09:28 am
content: that's my frequency standard

author: codeboy2k
author_rank: Super Contributor
timestamp: April 21, 2013, 03:15:41 pm
content: QuoteNicely done max-bitWould love to see bigger pics, and a description of whats inside and what's brought out on the output connections. You seem to have a rotary selection switch?? what's that for?I think I see a Rb reference, and maybe a GPS too?? please describe more !Thanks

author: max-bit
author_rank: Frequent Contributor
timestamp: April 21, 2013, 04:38:33 pm
content: Display bought in VK4GHZOther parametersPattern Trimble Thunderbolt GPS (bought on eBay)Distribution Amplifier based on BGA616 (siemens)4 out every 16 dBm at 50 OM

author: bingo600
author_rank: Super Contributor
timestamp: April 21, 2013, 04:50:25 pm
content: Quote from: codeboy2k on April 21, 2013, 03:15:41 pmI would have guessed Tbolt , the grey thing inside it looks like one my Tbolts ...Ohh and it also might look like a Cisco switcher ... I use those for Tbolts.What's the relay for on the distamp board ?/Bingo

author: max-bit
author_rank: Frequent Contributor
timestamp: April 21, 2013, 05:19:54 pm
content: The relay switches the power supply is delayed.So this power supply CiscoAnd it was at the start of the power they give some noise so used a delayIn addition, the system suppressor, the thyristors. As the voltage exceeds 10% thyristor turns on, and the fuse is burningSimple and effective

author: hairykiwi
author_rank: Contributor
timestamp: April 22, 2013, 11:33:47 am
content: Quote from: EEVblog on April 20, 2013, 10:55:15 pmThanks for the thoughts guys. To be fair, Kasper does say the Network Tranfer Frequency (NTF) project isbetterthan 1ppm.And after all Dave, you're on record as saying, "But hey, yeah, point six ppm - Good enough for Australia."OK, I admit, I'm taking your comment slightly out of context - but equally, a lot of hobbyists probably rely on a calibration lab to make the best of an "awful stock oscillator" in equipment like an Agilent 53131A. If they could achieve the same level of accuracy as you achieved with that Agilent Universal Counter using the NTF, like you say, "good enough".1ppm is a few orders of magnitude less than ideal for a true standard, I agree, but for those of us just starting out, or on limited budget, or only building 'hobby' projects, I'd argue it's all about making do. So it would bereally interesting toseehow much better than 1ppmthe NTF is - if anyone with a rubidium standard could spare the time pleaseIf anyone's willing, here's the NFT project file links again:n1.taur.dk/nft/nft.pdfn1.taur.dk/nft/nft.exeAnd if you could elaborate onhow manyorder's of magnitude better a frequency standardreally mustbe to satisfactorily calibrate a given counter for a desired level of accuracy, that would be useful info too.Just to put things in perspective, ±1ppm is ±0.0864 sec/day for a standard (typically 10 - 20 ppm) 32.768 kHz quartz crystal found in nearly all electronic wrist watches. That's ±2.6 sec/month - and although most electronic watch manufacturers don't advertise products with a spec that good, many achieve it. So everything's relative to its intended use. Speaking of which, the reason I'm really interested in all this 'making-do' is for calibrating the 32.768 kHz quartz oscillator in theOpen source Time Machine Project #2(OTM-02) - a watch module for hobbyists and makers using the latest 128 x 128Memory LCDandEFM32ARM Cortex-M3.Here's where the project's at as of a few days ago:I'll make a new thread in the EEVBlog Open Source Projects forum when I get a moment - and after getting the first code running later this week, all going well.Cheers guys - look forward to maybe seeing some results comparing Rubidium and NFT.

author: EEVblog
author_rank: Unknown
timestamp: April 22, 2013, 12:20:19 pm
content: Quote from: hairykiwi on April 22, 2013, 11:33:47 amA rubidium can be as low as $50 or so on ebay, so certainly well within the real of the hobbyist. How much does this NTF one cost?

author: hairykiwi
author_rank: Contributor
timestamp: April 22, 2013, 01:22:08 pm
content: Quote from: EEVblog on April 22, 2013, 12:20:19 pmThanks Dave, I'll start keeping an eye out for one.Any recommendations for brands/models to steer clear of? Or are they all likely to have reasonable life left in them for hobbyist use? The PRS10 I linked to earlier was on for £260.--The NFT doesn't involve any physical equipment purchase beyond buffering / level-shifting to a PC serial port.Here's an excerpt from the last page of Kasper's pdf instructions:"Generating the timing pulseTo be understood by a 115200N81 uart, the pulse must have a high (>+3V) time of 8-78?swhen arriving at the PC RXD pin. If you have a max232 or similar between what you aremeasuring and the PC, remember that it inverts the signal.If you generate the pulse using an output pin, it must be 8-78 us long, and less than 11kHzrepetition rate. A square wave of 6.4-11 kHz meets this, so 32768/4=8192 Hz would be agood choice.If you generate the pulse using a uart in a microcontroller, send a 0xFC character. Thebaud rate does not need to match as well as it does for data; A baud rate between 230400and 28800 will generate a usable character on the PC end."I've not yet had a chance to play with it - it's just been lurking on my things to investigate list and this frequency standard thread seemed like a good place to share it.BTW, In the example Kasper uses to illustrate the instructions, he achieves ±0.12ppm

author: kcozens
author_rank: Contributor
timestamp: April 29, 2013, 07:14:48 am
content: Quote from: EEVblog on April 22, 2013, 12:20:19 pmI'd be interested in one for $50. I have yet to see one for that price. The cheapest ones I've seen on eBay are the FE-5680 units for around $80+ plus shipping which pushes the combined price to around $100 and up.

author: rf-loop
author_rank: Super Contributor
timestamp: April 29, 2013, 08:50:03 am
content: Quote from: kcozens on April 29, 2013, 07:14:48 amTime ago there come suddenly lot of these to markets, more than enough. (just as before it happend with LPRO-101, and also with Trimble Tb GPSDO) Then they try fast change these lots of junk to money and there was many sellers... and they start competite with each others.. and market is saturated.. until there come buyers who start buy these after they find there is these available... now price is low... then sellers see that lot of peoples want buy... and here also Dave help sellers to rise prices in this FEI case. (junk do not mean they are bad or not useful but with sellers eyes and how they get these....)Sometimes in business is (in buyers side) wise to think how to share information to potential other buyers and how looud and much need open mouth.Perhaps some times ago it was gift from Dave to sellers they find these can sell more high price.As long as they can sell with higher price why they sell low price?

author: daddario
author_rank: Regular Contributor
timestamp: May 01, 2013, 06:41:41 am
content: Wow, the use of VDA's for splitting the reference signal really came as a suprise to me. But then again, I've never had any encounter in practice with these systems. But what really makes me wonder is... video uses a 75? system, but as far as I've understood the reference clock is distributed over a 50? system. Can someone perhaps enlighten me a bit or give some kind of a link explaining that?Pardon my ignorance.

author: Bored@Work
author_rank: Super Contributor
timestamp: May 01, 2013, 07:21:12 am
content: Quote from: daddario on May 01, 2013, 06:41:41 amIt is the external circuitry around the video opamp that determines the whole amplifier's output impedance. In fact, for line driving it is typically a simple series resistor at the opamp output. Make it 75 Ohm and you can drive 75 Ohm lines. Make it 50 Ohm and you can drive 50 Ohm lines.

author: ve7xen
author_rank: Super Contributor
timestamp: May 01, 2013, 07:21:37 am
content: So without a GPS antenna and the PPS light blinking on the Rb, is it phase-locking to a GPS receiver's unlocked clock? I don't see any alarm or 'GPS invalid' lights to indicate it's in holdover mode.I'd hope the CSIRO designed this properly, but have you checked Dave that you're not just calibrating against a TCXO disciplined Rb?

author: daddario
author_rank: Regular Contributor
timestamp: May 01, 2013, 08:13:19 am
content: Quote from: Bored@Work on May 01, 2013, 07:21:12 amBut that would assume modifying the stock unit. And, oddly enough, they seem to be using the original 75? connectors on the distribution outputs, as opposed to the correct 50? ones on the custom rubidium card(with the 1PPS, etc outputs).

author: SeanB
author_rank: Super Contributor
timestamp: May 01, 2013, 09:57:49 am
content: Video distribution amplifiers can drive 50R systems easily, you just change the drive resistor at the output from 75R to 50R, and note that you then have a fan out of 2/3 of before. So if each could do 30 then afterwards you can only drive 20 outputs.If it has a high impedance at the receive end so using a 75R terminator and the original wiring will work just as well, or a 25R series resistor just at the input of 50R terminations and then it still is terminated at the drive end and receive end correctly cable wise, just has a lower voltage level which is not a worry in this case which is using the zero crossings only.

author: LaurenceW
author_rank: Frequent Contributor
timestamp: May 01, 2013, 11:28:25 pm
content: I bought one of the FE5680 rubidium oscillators of FleaBay a while back (which STILL seem to be in plentiful supply), and put it in a nice case. From the outside, it all appears to work just fine. Once the "lock" light comes on, it is certainly locked to "something" (I have no higher reference to compare it against), and certainly the stability against my (20+ years old?) Option-fitted oven crystal osc in my HP5316 counter is impressive! Either that, or they both drift together... The two stay in step by better than two parts in 10^8. I'm impressed with the HP OCXO!In the UK, there used to be an impressive and free off-air standard of 15.625KHz, that being the line frequency (64uS) of good old analogue PAL TV transmissions. This was maintained for fun by the BBC to Better-than-I-ever-needed-it, and I used it to set up my HP OCXO a couple of years back. Sadly, this signal has dissapeared from the airwaves. So imagine my surprise to find that said HP OCXO was still within half a Gnat's Bollock of the FE5680, when I got that powered up!My "need" for accuracy extends to setting TCXO Temperature compensated crystal oscillators in regular time-of-day clocks to the best I can. With ~30,000,000 seconds in a year, if I can set a clock to keep better than 5 seconds drift per year, then I am happy (the TCXOs themselves in my designs are no better than that). So there it is right there - anything better than one part in 10^7 is all I need, personally. No - that won't win any awards - except the "entirely and sensibly fit for purpose" award, which is good enough for me.Some questions about Rubdium oscillators -> I hear talk of Rubidium tube life. Is that power-on hours, or total elapsed hours?> If the device is at least locking reliably (which seems to be the case), can I have confidence it must be working?> What might be the absolute error of an apparently locked oscillator? I have not attempted any rubidium adjustments.

author: grumpydoc
author_rank: Super Contributor
timestamp: May 02, 2013, 06:12:05 am
content: > I hear talk of Rubidium tube life. Is that power-on hours, or total elapsed hours?Power on hours for the Rubidium bulb.> If the device is at least locking reliably (which seems to be the case), can I have confidence it must be working?AFAIK, yes> What might be the absolute error of an apparently locked oscillator? I have not attempted any rubidium adjustments.Difficult since you don't know the provenance of one from the 'bay - the adjustment range is in the order of ± 2 x10-9so if someone's "tweaked" it, it at least shouldn't be more than that out.The one I have is within 1-2x10-11of my GPSDO,

author: bingo600
author_rank: Super Contributor
timestamp: May 02, 2013, 02:39:09 pm
content: AFAIK it's not wise to put a led directly on the FE-5680A "lock" pin.Someone mentioned that it will kill the 1-PPS , as 1-PPS "enable" is gated via this leg , and the led will pull the gate to low for the 1-PPS to go active (enable). They recommend some kind of driver for the LED./Bingo

author: kkp
author_rank: Contributor
timestamp: May 02, 2013, 06:05:00 pm
content: Quote from: LaurenceW on May 01, 2013, 11:28:25 pmI have repaired a couple of those. One failure mode in the FE5680A is the crystal oscillator drifting out of range. On the board, it's the crystal with a PTC soldered to it. On a good 5680A, during warmup, the frequency ramps between 4-8 ppm high, and many ppm low. So if the unit fails to lock when power cycled hot, you may need to tweak the trimmer to compensate for the aging of the crystal.Beyond that, if it locks in less than 5 minutes from room temperature, and never loses lock, it's good.I have one that is weak: It won't lock when hot if the frequency ramps more than 6ppm high during search, but once locked, it stays locked. I've put about a year's worth of runtime on it since then, and it still behaves exactly the same.One I tested was 10^-9 out, and the thing I learned from that is that you have to have it screwed to something. Not just for cooling, but to clamp the top and bottom mu-metal shields together.If you don't have a GPSDO, the next thing to get after an Rb is any kind of GPS receiver with pps output. Sometimes your friends will even give you one.Use your counter if you can, or cook up something with your favorite microcontroller to timestamp the pulses, and even a 250ns-jittering gps will give you 10^-12 over a day./Kasperwho is at the moment doing adev plotting on a free GPS from someone in this thread.

author: LaurenceW
author_rank: Frequent Contributor
timestamp: May 02, 2013, 08:02:37 pm
content: Thanks for those replies. Certainly, I load buffer all of the outputs from the reference, just in case of shorts, etc. I find myslef surrounded by GPS enabled devices, but none that specifically output a timing pulse! I've got a couple that stream bursts of Ascii data, and I recall that these bursts start at precise second intervals, so i will look at that. Otherwise, my oscillator locks fine, hot or cold, every time.

author: casinada
author_rank: Frequent Contributor
timestamp: May 02, 2013, 10:01:43 pm
content: Sync Wirelessly coming soonhttp://www.ecnmag.com/news/2013/05/nist-demonstrates-transfer-ultraprecise-time-signals-over-wireless-optical-channel

author: carloscuev
author_rank: Regular Contributor
timestamp: June 05, 2013, 05:42:53 am
content: I got a HP 53131A with 010 option, that is an OCXO reference, "High Oven" as HP calls it in the data sheet. Stability is 2.5 PPB (page 3http://cp.literature.agilent.com/litweb/pdf/5967-6039EN.pdf) but I don't know when was calibrated for the last time. Cal count is 7, the seller unfortunately removed stickers in an attempt to "clean it", apparently didn't know what he was doing. It was a bargain though. It is in good state, everything seems to work correctly, just little cosmetic damage.What I want to know how much I can rely in the measurements. The latest chip datecode is from 5th week of 1999, that was 14 years ago, data sheet states 15 ppb drift over 1 month, so i guess worst case scenario it has drifted (14*12*15) ppb, that is 2520 ppb, or 2.52 PPM? Is this right to assume?I'm thinking on getting a FE5680A to test them against each other, do you think this is a good idea, or the FE5680A could be even worse? Of course if I find that both of them are very close to each other I could be certain that both are on spec, but if difference is significant who could I blame for the difference, the HP "High" OCXO oven or the FE5680A?Any ideas are welcome, I just want to be confident about my measuring device.Thanks.

author: bingo600
author_rank: Super Contributor
timestamp: June 05, 2013, 12:39:12 pm
content: Quote from: kkp on May 02, 2013, 06:05:00 pmBlush ...

author: bingo600
author_rank: Super Contributor
timestamp: June 05, 2013, 01:24:57 pm
content: Quote from: carloscuev on June 05, 2013, 05:42:53 amGo for a GPSDOHis shipping to EU is usually to high for mehttp://www.ebay.com/itm/CIC-GGER-Equivalent-to-Z3815A-GPS-FREQUENCY-TIME-RECEIVER-10-MHz-/271213238400Untestedhttp://www.ebay.com/itm/HP-SYMMETRICOM-Z3805A-GPS-Disciplined-Oscillator-GPS-Frequency-Time-Receiver-/181113452077Testedhttp://www.ebay.com/itm/HP-SYMMETRICOM-Z3805A-GPS-Disciplined-Oscillator-GPS-Frequency-Time-Receiver-/290832846664Pricey but cool for a lab many 10mhz out - (seems to be of in the internal date) , but it won't affect the 10Mhzhttp://www.ebay.com/itm/Datum-9390-52054-GPS-Disciplined-10MHz-Atomic-Clock-Time-Receiver-IRIG-B-1PPS-/281073499525Both i and another person from this threadhas a Trimble Thunderbolt GPSDO (the old metal one)http://www.ebay.com/itm/Thunderbolt-PRECISION-GPS-10Mhz-1PPS-Standard-Easy-Kit-/180419218430http://www.ebay.com/itm/Thunderbolt-PRECISION-GPS-10Mhz-1PPS-Standard-Easy-Kit-/280649244485http://www.ebay.com/itm/ThunderBolt-GPS-Disciplined-Clock-10-MHz-and-1-pps-/271207827869But we got them before the prices skyrocketed (Back then it was $110 for a unit , and $200 for a kit)Remember an antenna (5volt)I prefer timing antennas , but have also used normal marine antennashttp://www.ebay.com/itm/GPS-Timing-Reference-Antenna-26db-Gain-N-connect-/270881742870http://www.ebay.com/itm/PCTEL-MAXRAD-GPS-26dB-TIMING-REFERENCE-ANTENNA-KIT-GPS-TMG-26NMS-NEW-/121121457131http://www.ebay.com/itm/Nokia-470290a-101-Timing-Reference-Antenna-20-db-N-type-GPS-Waterproof-antenna-/290853216689I think this is the one Trimble uses for the Thunderbolt.http://www.ebay.com/itm/trimble-gps-antenna-p-n-28367-70-/290508227053The HP/Symetricomm GPSDO's are good but prob need 24 or 48volt , so keep an eye on the power requirements.And N-Connectors for the Antennas ....Well this should give you a hint ..../Bingo

author: carloscuev
author_rank: Regular Contributor
timestamp: June 05, 2013, 01:59:37 pm
content: Quote from: bingo600 on June 05, 2013, 01:24:57 pmWOW $110 for a GPSDO, that would have been great. Sadly I panicked about a FE5680A at $89 (free shipping) on ebay and already bought one, the next cheap one is about $120 (incl. shipping). At least the seller claims it's one of the latest UN-7XXXXX models available from eBay with 2004 manufacturing date. Having bought the counter and the rubidium standard, I have left about 30-40 bucks.How difficult could it be to later make a GPSDO using this FE5680A and a GPS receiver with 1 PPM output? Any place to start reading the basics about how to do it?Is there any GPS receiver unit recommended for this? Maybe I can afford a cheap one.Anyway, I hope the OCXO in the HP counter is working good, seller claimed last calibration was in 2010, but cannot trust him because he doesn't seem knowledgeable about test equipment, he mainly sells used low end audio stuff.

author: EV
author_rank: Frequent Contributor
timestamp: June 05, 2013, 03:42:32 pm
content: Quote from: carloscuev on June 05, 2013, 01:59:37 pmFE5680A is good but it is not easy to trim to correct frequency.http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5680a_faqNow you need also GPSDO and your counter to check this FE5680A.You can do GPSDO yourself or buy a kit:http://www.jrmiller.demon.co.uk/projects/ministd/frqstd0.htm

author: carloscuev
author_rank: Regular Contributor
timestamp: June 05, 2013, 04:21:27 pm
content: Quote from: EV on June 05, 2013, 03:42:32 pmI was afraid of that.Quote from: EV on June 05, 2013, 03:42:32 pmI think I'm going to go with this alternativeThere are several 10Mhz OCXOs in eBay:http://www.ebay.com/sch/i.html?_odkw=OCXO&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR11.TRC1&_nkw=OCXO+10Mhz&_sacat=0Which one should I go for? Could I assume anyone would work because it will be disciplined by th GPS?About the GPS, I've seen lots of odules on eBay with SiRF 2, 3 and 4, any recommendation? is the bigger SiRF chipset version, the better?There's an interesting Fastrax UC430 that includes a chip antenna, has 1 PPS outputhttp://www.ebay.com/itm/190849374321Also a chinese SIMCOM module, not sure if it has 1 PPS outputhttp://www.ebay.com/itm/180795135748There are also some Globalsat models, they have 1 PPS outputhttp://www.ebay.com/itm/140976661175Sorry for all this questioning, I'm a long time hobbyist, but just starting to learn all this precise timing arts.

author: EV
author_rank: Frequent Contributor
timestamp: June 05, 2013, 04:49:49 pm
content: I have some of these:http://www.ebay.co.uk/itm/Navman-jupiter-T-Tu60-GPS-Kit-1pps-10khz-GPS-Module-/260790984470?pt=US_Ham_Radio_Amplifiers&hash=item3cb85a9f16and these:http://www.ebay.com/itm/10MHZ-ISOTEMP-Reserch-OCXO-134-10-CRYSTAL-OSCILLATOR-/170489162873?pt=LH_DefaultDomain_0&hash=item27b1f22c79and I have bought some PCB's from Miller to make control board for them. I have however not assembled them yet, maybe next winter time I do it. I have a trimble thunderbolt GPS disciplined standard already, so there is no hurry.

author: EV
author_rank: Frequent Contributor
timestamp: June 05, 2013, 04:56:00 pm
content: This one is without the control board which is not needed:http://www.ebay.com/itm/Navman-Jupiter-T-GPS-Module-Empfanger-TU60-10khz-1pps-/290860812674?pt=DE_Handys_Kommunikation_Messger%C3%A4te&hash=item43b8a7c982

author: bingo600
author_rank: Super Contributor
timestamp: June 05, 2013, 07:02:12 pm
content: @CarlosYou'd need the GPS receivers that EV points at if you build the Miller GPSDOThe design relies on the 10Khz output from the Jupiter's , 1PPS is not going to do it.For a really nice 1PPS receiver , get this one (supposed to be among the best)http://www.ebay.com/itm/Motorola-ONCORE-M12-T-timing-gps-receiver-1pps-100hz-/290656401551/BingoOhh i just found this one - more reasonable pricehttp://www.ebay.com/itm/TRIMBLE-GPS-RECEIVER-10MHZ-CLOCK-THUNDERBOLT-/171048961859The TBolt needs 5v and +/- 12v , you can use a Cisco 1700 powersupply .. like herehttp://www.ebay.com/itm/Thunderbolt-10mhz-GPS-Power-Supply-30W-12V-12V-5V-/280703342103Or any reasonable clean switchmode , even though linear would be best.I use a Cisco PSU ....And you could start out with a cheap 5v gps antennahttp://www.ebay.de/itm/OPEK-3V-5V-GPS-1102-Active-Antenna-for-Garmin-G5010U-5M-/140892128742

author: EV
author_rank: Frequent Contributor
timestamp: June 05, 2013, 07:53:11 pm
content: Quote from: bingo600 on June 05, 2013, 07:02:12 pmI have two antennas like this in use and they work very well. I have installed the reciever and the power suply to the same case. They can be seen in the next link.http://www.ebay.co.uk/itm/Easy-Kit-Thunderbolt-PRECISION-GPS-10Mhz-1PPS-Standard-/280649530260?pt=LH_DefaultDomain_0&hash=item415803fb94Picture about the finished device is attached.

author: zibadun
author_rank: Regular Contributor
timestamp: June 05, 2013, 08:49:26 pm
content: I've got one of those HP Z3805A units. It works flawlessly and has many outputs, including Rs232. They used to cost a lot more (around $400) a few years ago before a truckload of thunderbolts appeared. I think it's a bargain at the current price.3805 usually sold without an antenna but it Works with most "active" gps pucks. It may show an alarm light because the new antennas draw very little current and the device thinks it's unplugged. The trick is to add a resistor between the center conductor and ground of the coax connector. Don't believe this affects the accuracy. Don't forget the setting for coax propagation delay which based on the cable length and velocity factor. a guesstimate is probably ok here