Rubidium Standards on eBay - Any good? - Page 1
Forum section: electronics / testgear

author: echen1024
author_rank: Super Contributor
timestamp: August 11, 2013, 04:19:20 pm
content: Being sort of a cheapskate, I have seen these Rubidium Standards on eBay for under $100. I am wondering if they are any good, and also about the accuracy of these units. I envision a nice project to build an atomic clock.eBay auction: #http://www.ebay.com/itm/FE-5680A-Rubidium-Atomic-Frequency-Standard-10MHz-out-/280655233263?pt=LH_DefaultDomain_0&hash=item41585b00ef

author: IonizedGears
author_rank: Regular Contributor
timestamp: August 11, 2013, 05:15:44 pm
content: They are really good for accuracy and the reason they are being sold so cheaply is that these rubidium standards are constantly replaced by newer standards for their use in cellphone antennas.

author: grego
author_rank: Frequent Contributor
timestamp: August 12, 2013, 12:11:32 am
content: Note though that they are replaced in the field constantly because they are only good for so long before their accuracy decays (get it? "decays" and rubidium - I crack myself up). The issue with the ebay ones is you don't know how long they have been deployed -- the thing about these standards is it doesn't matter how long they have been active, it just depends on their manufactured date.That being said they are accurate as can be while still in their "good" phase.

author: echen1024
author_rank: Super Contributor
timestamp: August 12, 2013, 12:22:49 am
content: Quote from: grego on August 12, 2013, 12:11:32 am

author: pickle9000
author_rank: Super Contributor
timestamp: August 12, 2013, 12:35:00 am
content: The sad part is you could get them for under 40 bucks a couple years ago.

author: JoeyP
author_rank: Frequent Contributor
timestamp: August 12, 2013, 04:59:38 pm
content: I bought a few within the past year, and found them to be stable and to agree with each other within a few parts in 10^10. Have not tested them against a traceable source, but they have plenty of adjustment range so would expect no problems in getting them calibrated.

author: jamesb
author_rank: Regular Contributor
timestamp: August 12, 2013, 06:21:27 pm
content: I wonder which isotope is primarily used in Rb standards.87Rb has a half-life in the 1010year range IIRC.So what (other than shorter half-life isotope use) would account for the drift? Admittedly, I am not really up-to-snuff on the physics package used, etc.

author: edpalmer42
author_rank: Super Contributor
timestamp: August 12, 2013, 06:25:24 pm
content: Quote from: grego on August 12, 2013, 12:11:32 amCute, but no, they don't 'decay'. I don't know where you heard that they age even when turned off, but I've never come across that. I have Rb standards that are over 20 years old and are still going strong. Like any piece of electronic equipment they can have random failures, but there are no defined wearout mechanisms in an Rb standard. People often talk about the Rb lamp that exists in every Rb standard as being a weak point, but I've had very good luck with these devices.It seems like all the units coming out of China have basically been dug out of a scrap heap so you could get a dud. But I've heard that various vendors have been good about replacing defective units. Check the vendor's reputation - not just on ebay - do a google search for references in forums like this.Ed

author: grego
author_rank: Frequent Contributor
timestamp: August 12, 2013, 06:39:36 pm
content: Most standards only have about 100uG of Rubidium in the lamp. That's to avoid flicker on the lamp - but it does "wear out" - it's a part like any other. Best way to find out is open the case on it and check the voltage -- "healthy" lamps are (from what I've read) in the 6 to 9 volt range.The issue with the ebay ones is you just don't know how long they've been running or how much lamp life is left.Rubidium does decay BTW - it's just got a half life of sometihng like 149 billion years so you won't run out of that resource.

author: ddavidebor
author_rank: Super Contributor
timestamp: August 12, 2013, 06:43:49 pm
content: Quote from: echen1024 on August 11, 2013, 04:19:20 pmThey're good if you need a transfer standard, but if you can, gpsdo (professional, not diy) are better for lab reference.

author: rudika79
author_rank: Regular Contributor
timestamp: August 12, 2013, 07:25:28 pm
content: I bought one FE-5680 Rubidium Standard two weeks ago. You need to look out which unit you buying because with same model number there different configuration. Example one have 10MHz output or another don't have, some unit you can program the output frequency like frequency generator, some unit just have 1PPM output. My unit have 1PPM output and no 10MHz output. I need to open the box and solder coax cable between output connector (9pin sub-d)and a DDS board (small coax connector) as well I needed to solder another two wire for RS232 control signal for DDS Chip. In my unit DDS board was set to 8.366 MHZ and I needed to reprogram to I can have 10MHz output. Another think, you need to be careful with information what can you find on internet, because most off information is inaccurate. I suggest to watch Dave's and Gerry's videos about this rubidium standard.Gerry's Video:http://gerrysweeney.com/i-need-10mhz-how-hard-can-it-be/Rudolfp.s. After my modification I didn't checked yet a accuracy but pretty much should be in specification. That is my next project to compare to my gpsdo.

author: jamesb
author_rank: Regular Contributor
timestamp: August 12, 2013, 07:44:26 pm
content: Quote from: grego on August 12, 2013, 06:39:36 pmSo, unless I remember my nuclear chemistry incorrectly, the first-order rate of decay would dictate that after 1010years you would have only 50ug of Rb .. which suggests that, with 10 years being many orders of magnitude less than the 1010half-life, you would effectively have 99.999999999uG remaining (back-of-the-envelope math aside).Is there some other mechanism which would be responsible for the drift as opposed to isotope extinction?

author: dfmischler
author_rank: Frequent Contributor
timestamp: August 12, 2013, 07:58:52 pm
content: "A Mechanism of Rubidium Atomic Clock Degradation: Ring-Mode to Red-Mode Transition in rf-Discharge Lamps" by Camparo, J. Mackay, R.Abstract:In the vapor-cell atomic clock, long-term stability can beinfluenced by slow variations in the discharge lamp's output via thelight-shift effect. Additionally, over a multi-year mission lifetimethe lamp's aging can degrade its optical pumping efficiency.Understanding the mechanism(s) that drives these changes isparticularly important for spacecraft devices, where the atomicclocks are called upon to function continuously and reliably formany years. Here, we consider the two well-known, but littlestudied, modes associated with alkali rf-discharge lamp operation:the ring mode and the red mode. Consistent with previous research,we find that the ring mode is best for optical pumping, and that theclock-signal amplitude degrades significantly when the lamp operatesin the red mode. Examining the emission spectrum as the lamptransitions between these two modes, we show that the ring-mode tored-mode transition is driven by radiation trapping within the lamp.

author: jamesb
author_rank: Regular Contributor
timestamp: August 13, 2013, 12:01:11 am
content: Awesome - thanks for pulling that reference. I'll check Google scholar to see if I can find free access

author: Dr. Frank
author_rank: Super Contributor
timestamp: August 13, 2013, 08:32:43 am
content: Hello,the ageing and failure mode of the Rb clocks mainly origins from the permanent deposition of Rb on the inner side of the glass tube.That is visible as a metallic film inside this tube, but I don't remember, which one of the two heated tubes is affected.In the time-nuts community, one guy successfully refurbishes old Rb clocks with too low monitor voltage by disassembling carefully the physics package, and heating the affected tube with a hot air gun until the Rb film is vaporized again.Afterwards, the monitoring voltage and the stability should be as good as new.Depending on the model offered, there are also some electronic components (i.e. one certain resistor) which are known to fail regularly, but can easily been tested & replaced.There exist several repair descriptions for that.The rejuvenation on a FRS is described by G. Molenkamp:http://www.vk3um.com/Rubidium%20rejuvination.pdfFrank

author: grego
author_rank: Frequent Contributor
timestamp: August 13, 2013, 12:26:33 pm
content: Quote from: Dr. Frank on August 13, 2013, 08:32:43 am"Time nuts community". I love it. Cracked me up.

author: dfmischler
author_rank: Frequent Contributor
timestamp: August 13, 2013, 01:23:33 pm
content: Quote from: grego on August 13, 2013, 12:26:33 pmNo, really.Time Nuts Archives August 2013

author: macboy
author_rank: Super Contributor
timestamp: August 13, 2013, 01:37:26 pm
content: That's right, the Time Nuts are as real as the Volt Nuts.

author: Dr. Frank
author_rank: Super Contributor
timestamp: August 13, 2013, 01:51:16 pm
content: Quote from: grego on August 13, 2013, 12:26:33 pmPay attention buddy, Lady Heather might discipline you...(Just search for her)