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Ebay Frequency Standards-Rhubidium and OCXO

Discussion in 'Homebrew and Kit Projects' started by K9TW, Mar 13, 2012.

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  1. K9TW

    K9TW Ham Member

    I am thinking about buying either a OCXO or a Rhubidium frequency standard for use as time base for my service bench frequency counters and signal generators. I am going to Dayton Hamfest and hope to find something there. If not, I have been looking on Ebay and see couple of Chinese suppliers of both types of 10 Mhz standards. Does anyone have any experience buying from these suppliers?

    I see the OCXOs are at least half the price of the Rhubidiums. I dont want to get too anal about this and not ready to look at GPS based units at this time.

    Any counsel would be appreciated as to which standard to buy and if there is one Ebay dealer more reputable than another.

    Thanks
    Terry K9TW
     
  2. KD0CAC

    KD0CAC Ham Member

    I have come across a lot of activity about those recently , maybe some upgrading has hit the surplus market as I remember , looking into the same .
    Some groups I have been monitoring this subject with have been ,
    TimeNuts
    Hackaday
    EEVblog
    and a local Ghz guy NLRS , Northern Lights Radio Society
     
  3. WA6TKD

    WA6TKD Ham Member

    I would think that a OCXO would be more then sufficient as a local 'bench standard'. Those Rubidium frequency standards are impressive but are more complex with certain components with finite lifespans, they just have more to go wrong in them. They are pulls from older cell phone equipment that have been upgraded or replaced. If you do go with a 10Mhz OCXO be sure you get the output type you want, sine-wave or square-wave.
     
  4. G0HZU

    G0HZU QRZ Member

    I recently bought an item from (chinese) ebay seller 2010bluebook who also sells the rubidium standards.

    My item was an Anritsu N type 50 ohm termination (12GHz) and it was sent on free delivery for $25.

    I was a bit worried at first (because it was such good value) but the item arrived three weeks later as described and it tests out fine on a microwave VNA. You also get a tiny free toy doll/bear with the sale and I think it's to do with the chinese customs as the parts are marked as used ham radio items when they arrive and the parcel has various stickers on it to do with export control and customs etc.

    The ebayer seems VERY keen to maintain good feedback and includes a letter with the item to reflect this so I think this seller is OK :)
     
  5. G0HZU

    G0HZU QRZ Member

    Personally, I'd go for the rubidium standard as the OCXO specs from the same vendor are very good but not 'fantastic' by today's standards.

    eg I have various frequency standards here and one is very similar to the Isotemp part. Mine is 5 parts per billion over -20 to +70degC (Quintenz) and it is nearly 10yrs old.


    However, it's the ageing spec that is most critical and mine does need a minor adjustment every year or so when measured against an offair standard. I'm tempted to go for a GPS based standard once the local offair (198kHz) transmitter at Droitwich shuts down in the near future. About 15yrs ago I designed and built my own 10MHz offair standard to lock to this local transmitter and pretty soon it is going to be redundant as they are running on their last set of transmitter tubes...

    http://en.wikipedia.org/wiki/Droitwich_transmitting_station
     
  6. K9TW

    K9TW Ham Member

    Thanks to all this is exactly info I was hoping for. I did see the bluebook seller. Also, I had not thought about sine vs square wave output. I had never heard of Droitwich very interesting.

    I will wait and see how I can do at Dayton on either type unit. If no go there then will have to decide on OCXO vs Rhubidium and take my chances on Ebay. Probably should have gotten the Rhubidium several years ago when they were half or less of going price today.

    I saw a Thunderbolt GPS unit on QTH not long ago, but it was $300 and I dont want to get that much involved. Tnx and 73s Terry
     
  7. LU1AR

    LU1AR Ham Member

    I bought a Rubidium Standard and was received with free delivery to Argentina (ยก!). They need 18 VDC 2 A. peak, 900 mA running and 5 VDC 300 mA. After warming inside, give negative a logic state. I used to light a LED, conected to the +5VDC line.
    The unit is surplus from Cellphone base stations and run OK. You will have a privillege to use a Rubidium Standard in your shack.
    Any trouble related with aging is no significative in the environment of amateur use. The worst Rubidium Standard is an order of magnitude better than the best OCXO.
    Regards.
    Edgardo
     
  8. W9GB

    W9GB Ham Member

    Terry -

    You don't need to spend that much.
    I have a Thunderbolt GPS unit here, if you wanted one badly.

    w9gb
     
  9. WA7PRC

    WA7PRC Ham Member

    Like Edgardo/LU1AR, I recently purchased a used Frequency Electronics pn FE-5680A rubidium standard from eBay... less than $50 including shipping. While the datasheet says it wants 15 to 17VDC, it runs fine on 13.8V. It also needs 5VDC. Output is sinewave 10MHz @ +7dBm.

    I plan to use it with my TS-850S and an interface that also came from eBay. The interface is an active doubler. Its current monitor will tell the TS850 whether to use the internal or external reference. I'm way ahead of buying a TCXO, in terms of both cost and precision. :)
     
  10. K9TW

    K9TW Ham Member

    I sent you a response to your ARRL.Net email address to discuss this off list. My email is wagstw46@aol.com. Thanks Terry
     
  11. K9TW

    K9TW Ham Member

    Do these Ebay sellers of the rubidium standards have some means of checking the accuracy of the 10mhz output? I assume there is some type of internal cal trimmer and how do I know hasnt been tweaked? Are they just selling surplus pulls from Cell Phone industry and trusting they are accurate and have sufficient remaining life or do they have lab standards to check performance before selling?
     
  12. WA7PRC

    WA7PRC Ham Member

    I didn't ask the seller; I did my own research. The frequency of the VCO is locked to that of a Rubidium lamp. It takes a few seconds for the lamp to warm up, and then the unit gives a "Lock" output. Upon cold-start, I hear a beat note between it and 10 MHz WWV. In 10 or 20 seconds, it pulled-in and I heard no more beat note. A Google search will find a plethora of information. I have mine enclosed in a chassis with decoupling on the DC input, LED monitoring, and output interfacing.
     
  13. K9TW

    K9TW Ham Member

    Bryan: Yes I assumed you could use WWV as your primary standard to compare it to. I have done that over the years with xtal calibrators. However it requires good strong WWV signal and how touchy the trimmer is. Can probably get it within a hz. I have played around using O-scope and audio spectrum analyzer software to look at the beat note.

    I think I will email couple of the ebay rubidium standards sellers (I am leaning toward the LPRO-101) and ask them if they have a lab and if they use a primary standard to check the units they sell and what their standard is. Should be interesting.

    I guess by using WWV at minimum you could tell if it someone had tweaked it and it was grossly off. That was my main concern.

    As I think about it I suspect a OCXO would be accurate enough as a portable standard and less costly and not have to worry about the aging aspect.

    Appreciate your response. I have more homework to do. Happy Easter to all. Terry K9TW
     
    Last edited: Apr 8, 2012
  14. NR8O

    NR8O Ham Member

    Terry, good post. I didn't even know about rubidium standards until I came across your post! I spent a couple of hours today surfing the web and reading up on both rubidium and gps freq standards. I guess you're taking a gamble with these pulls since you don't know how much life is left in the rubidium lamp. Anyway, I have a HP 8657D signal gen sitting here that I'd like to get a standard for, and I'm not sure if I can wait until Dayton. ;-) Keep us updated on what you end up... 73, Ron NR8O
     
  15. K9TW

    K9TW Ham Member

    Ron: Take a look at Iso-Temp OCXO model 134-10. Can find these on Ebay for around $50.00. I plan to look for one of these at Dayton in addition to the Rubidium. I think either would be good for ham service bench, but as always what will be your primary source to ensure the OCXO or Rubidium is accurate? It appears to me you have choice between WWV and GPS. If you get the Rubidium look on Ebay for a "rubidium lock". WA3IAC sells a kit that lights an LED to indicate when it has locked. It comes with PC board for around $6.00. Terry K9TW
     
  16. K7MEM

    K7MEM Ham Member

    Rubidium based sources go back over 30 years so I would think the newer ones, even if they are pulls, should be higher quality than the ones I dealt with 30 years ago.

    Around 1979 I was involved in a project that required two coherent frequency standards for use at 18 GHz. We started with the 10 MHz sources but they were not stable enough. We went back to the manufacturer and had them create a 5 MHz version. To test their stability, we then took the 5 MHz sources and added battery operation and the necessary RF circuitry to get the signal to 18 GHz. One source would be used in a transmitter and the other in a receiver. Once the batteries were charged, we would disconnect them, so each unit ran independently of the other. We then took the 18 GHZ signals from each unit and ran them into a Mixer. What we expected was a stable DC note on the output. The 18 GHz output was then connected to a A/D converter and a computer (PDP-11/34) collected I and Q data over a span of 12 hours. We didn't have a problem with them drifting slightly from each other, as long as we could predict the drift. The drift data could then be included in the signal processing.

    We found that although the drift was generally no more than 1 Hz, it was very difficult to predict. At the time, these sources cost around $10,000 each and were not very reliable. We had to swap sources many times before we got two that were reliable. Part of the reliability issue was that they had to work in aircraft, so the sets were run with then strapped to shake tables.

    The company wanted me in Germany for the next 3 or 4 years so I had to pass my knowledge to someone else. I never really found out how they did. I do know that when I came back from Germany (1984) the program was still active. So either they made a lot of progress or they got really good at dancing around the issues.

    I really don't think that many people have the need for anything as stable as these sources, bit, if you can get one for around $50 now, I would say it's a great investment. At those prices, why not buy two? If it goes bad, you can always swap in the spare.
     
  17. WD5HHH

    WD5HHH Ham Member

    Rubidium Standard Uncertainty

    In reply to a few of the above, you cannot compare a rubidium standard to HF WWV once the rubidium standard has stabilised. There are too many frequency errors introduced by propagation into the over-the-air frequency to approach the native accuracy of the rubidium standards. The only comparisons that can be made are against caesium standards. This can be done either directly or via GPS disciplining. The latter will introduce about a half-magnitude error. However, for most amateur use the difference is inconsequential. I speak to this from having spent 10 years as an engineer in a metrology lab. We used a GPS disciplined frequency standard since we could not afford a caesium standard. It was considered traceable and in no need of any other calibration. It has been 10 years since I left that work but at the time I understood all of the "why" behind the uncertainty of the lab standard.
     
  18. NR8O

    NR8O Ham Member

    Thanks for the info guys, I'm learning a lot. So it looks like there are several options. The rubidium pulls on eBay, although from reading the time-nuts mailing list I missed out on the $39 (with shipping) pulls that a bunch of the guys were buying back in January. The least expensive ones now are in the $70-$80+ range, shipping included from China. There is a guy selling the Trimble Thunderbolts for $169 shipped. Another route might be to pick up a Navman jupiter T Tu60 GPS board, being sold by user nhbbobb1985 on eBay with interface board for $65, and phase lock it to an ovenized 10Mhz crystal oscillator. All overkill for what I personally would be using it for, but pretty neat knowing this kind of accuracy is available...
     
  19. WA7PRC

    WA7PRC Ham Member

    Exactly. I have my FE-5680A mounted in a chassis to allow for interfacing, with some added PS decoupling.

    $70-80 is still dirt cheap, compared to anything else you can find. With the interface board kit that fits in place of the TCXO in my TS850, I've spent less than the cost of Kenwood's TCXO, and have much better precision & stability. The interface board is smart enough to know when the external reference is lost, and enables the OEM xtal oscillator.
     
  20. KV6O

    KV6O Premium Subscriber

    I have been eyeing one of these, but haven't pulled the trigger on one yet. My current reference is a HP OCXO and it gets me within 1/2 a Hertz on the Frequency Measurement Tests...

    BTW, there is a FMT next Thursday - perfect opportunity to put your new rubidium source to work!

    http://www.arrl.org/frequency-measuring-test

    Steve

    KV6O
     
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