Author Topic: Eevblog #235 - Rubidium Frequency Standard  (Read 30284 times)

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Offline Blue

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Eevblog #235 - Rubidium Frequency Standard
« on: January 13, 2012, 01:31:35 am »
Nice  :)

 

Offline Blue

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #1 on: January 13, 2012, 01:32:50 am »
Sinus output looks a bit wierd.

Dave, Is there a calibration screw cap inside?
 

Offline Neganur

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #2 on: January 13, 2012, 03:20:44 am »
There was something about those 5V, I can't remember properly but I think they were not needed and actually harmed internal circuitry.

I may be able to dig up the info somewhere again.

Edit: never mind, that was regarding 5V on pin 3 (the lock indication). The 5 V are for the internal DDS.
« Last Edit: January 13, 2012, 03:59:23 am by Neganur »
 

Offline benemorius

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #3 on: January 13, 2012, 04:06:06 am »
http://www.vk3um.com/Rubidium%20Standard.html

There was apparently some bad pinout information at some point directing people to apply +5v to pin 3, which is actually the active low lock output. This went unnoticed by some since the 5v rail would be powered by the clamping diode in the IC connected to pin 3 and the device would function, but then someone opened one up and caught the error. Pin 4 is apparently the correct pin for +5v.
 

Offline tnt

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #4 on: January 13, 2012, 05:19:56 am »
There is a _lot_ of variations of those Rb standard ... all with the same reference number and all different inside.
The one Dave has is one of the more recent one. It has a different architecture than the previous ones. It's not programmable but it is trimmable via the RS232.

The "sinus" is the output of a Xilinx CPLD filtered through a LC filter inside and then again though that special "filtered" DB9 connector (it's _not_ a simple DB9, each pin is actually a small filter !)

If you probe the sinus at it's source (you'll see a small miniature rf connector inside), you'll see it looks awful there ...
 

Offline EEVblog

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #5 on: January 13, 2012, 07:39:26 am »
Is anyone seeing any/video sync problems on this video?
I can't see it, but I've had two people report it.
I hope it's not my new video editor VideoPad causing problems.
But I thought Youtube re-encodes all uploaded videos, so I'd expect everyone to see any problems.

Thanks
Dave.
 

Offline benemorius

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #6 on: January 13, 2012, 07:44:53 am »
Is anyone seeing any/video sync problems on this video?
I can't see it, but I've had two people report it.
I hope it's not my new video editor VideoPad causing problems.
But I thought Youtube re-encodes all uploaded videos, so I'd expect everyone to see any problems.

Thanks
Dave.

I didn't notice any such problems. I don't suppose anyone mentioned any specifics?
 

Offline EEVblog

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #7 on: January 13, 2012, 07:46:44 am »
Is anyone seeing any/video sync problems on this video?
I can't see it, but I've had two people report it.
I hope it's not my new video editor VideoPad causing problems.
But I thought Youtube re-encodes all uploaded videos, so I'd expect everyone to see any problems.

Thanks
Dave.

I didn't notice any such problems. I don't suppose anyone mentioned any specifics?

Nope, just "outa sync"  ::)

Dave.
 

Offline rf-loop

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #8 on: January 13, 2012, 07:56:14 am »
Sinus output looks a bit wierd.

Dave, Is there a calibration screw cap inside?

Sinewave is distorted but looks normal for this Rb, this do not affect frequency accuracy.

C-Field adjustment is behind small hole on left long side.
If adjust it need good reference and enough accuracy counter. Not this philips.
Or it can do also with oscilloscope with enough good frequency reference. Example GPS disciplined OCXO or Rb.
(without oscilloscope it need least frequency counter what resolution is minimum 1mHz @ 10MHz or better and enough accurate reference. With oscilloscope it need only enough accurate reference and waiting long time for look phase drift.
If not enough good test posibility better to keep fingers out from C-Field adjustment. Becouse normally these have still "good" accuracy (oh well... what is "good" accuracy... of course they are not inside +- 5x10exp-11 error window (mostly) but maybe inside +-10x10exp-10 after long time use without calibrating. )

This Rb model serie have really lot of variations as someone tell.
I have some of these models. Some of these can "program" to different frequency using inside RS232. But only some models.
Also difficult to find good documents.  10MHz output need 50ohm load afaik. (but also this may have variations)
« Last Edit: January 13, 2012, 08:20:25 am by rf-loop »
If practice and theory is not equal it tells that used application of theory  is wrong or the theory itself is wrong.
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Offline IanB

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #9 on: January 13, 2012, 08:02:06 am »
Nope, just "outa sync"  ::)

Dave.

It might be the player. Just lately I've noticed a few videos with the audio badly out of sync (2-3 seconds), from many different uploaders. I can't imagine every case is a problem with the original content, so my bet is the trouble lies at YouTube's end.
I'm not an EE--what am I doing here?
 

Offline Zad

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #10 on: January 13, 2012, 08:18:16 am »
Aaah that explains it. I have just posted a comment on YouTube about that. The "sine" wave is absolutely awful! It must generate an amount of jitter when you try to sync it. Simple enough to amplify and clip to a square wave though I guess.

An alternative method is to get a crystal oscillator (preferably TCXO or OCXO) and constrain it to a GPS 1pps pulse. This actually gives a better signal than rubidium sources. GPS has a phenomenal long term accuracy, but even on a good receiver the pulse jitter is +/-50nS. Conversely, the crystal oscillator has a relatively poor long term drift stability by a very clean and regular short term Tau. Combining the two with a locking loop gives an extremely good frequency source.

This is a good place to start when looking for into on time and frequency geekery: http://www.leapsecond.com/

Offline EEVblog

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #11 on: January 13, 2012, 08:21:47 am »
It might be the player. Just lately I've noticed a few videos with the audio badly out of sync (2-3 seconds), from many different uploaders. I can't imagine every case is a problem with the original content, so my bet is the trouble lies at YouTube's end.

Good to know, thanks.

Dave.
 

Offline wkb

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #12 on: January 13, 2012, 08:46:36 am »
It might be the player. Just lately I've noticed a few videos with the audio badly out of sync (2-3 seconds), from many different uploaders. I can't imagine every case is a problem with the original content, so my bet is the trouble lies at YouTube's end.

Good to know, thanks.

Dave.

Just watched the video (on a Mac), no problems that I noticed. YMMV ?
 

Offline Chet T16

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #13 on: January 13, 2012, 08:55:59 am »
Definite sync issue my end, only very slight and i can only notice if i look at your mouth moving.

Why does this come with an OCXO?
Chet
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Offline firewalker

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #14 on: January 13, 2012, 09:08:04 am »
With the Agilet LCR meter it was bad. 1~3 seconds. Only on 720,1080p. This episode was ok. It must be Google's issue.

Alexander.
 

Is anyone seeing any/video sync problems on this video?
I can't see it, but I've had two people report it.
I hope it's not my new video editor VideoPad causing problems.
But I thought Youtube re-encodes all uploaded videos, so I'd expect everyone to see any problems.

Thanks
Dave.
Become a realist, stay a dreamer.

 

Offline EEVblog

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #15 on: January 13, 2012, 09:12:12 am »
With the Agilet LCR meter it was bad. 1~3 seconds. Only on 720,1080p. This episode was ok. It must be Google's issue.

That might say something, because I started using VideoPad instead of Sony Vegas with the Agilent LCR episode.

Dave.
 

Offline firewalker

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #16 on: January 13, 2012, 09:58:43 am »
I will try the LCR episode again (when in front of a PC capable for HD res). I will also download the episode directy from youtube for off line playing to test it.

Alexander.
Become a realist, stay a dreamer.

 

Offline PeteInTexas

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #17 on: January 13, 2012, 10:14:04 am »
Is anyone seeing any/video sync problems on this video?
I can't see it, but I've had two people report it.
I hope it's not my new video editor VideoPad causing problems.
But I thought Youtube re-encodes all uploaded videos, so I'd expect everyone to see any problems.

Thanks
Dave.

How many hours upon hours have you wasted wrestling with video editors and editing and YouTube and servers and such?  Don't you think your fans would rather see you wrestling with electronic curiosities?  It may be time to start thinking about bringing in an intern who wants to build their experience with these things.  I'm sure the local community college has students eager to work on something.  They might even have access to better editing equipment and software at their lab.

I understand you are having a great time and all but if you want your blog to "scale", letting go of some of these routine task is inevitable.  Not trying to be rude or anything, just rather see you doing electronics instead.   ;D :-[ (can't find a fitting smiley to convey my deference to you in making such a suggestion)
 

Offline Zyvek

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #18 on: January 13, 2012, 10:28:40 am »
Dave, I think (meaning I'm probably wrong) all of the 5680A's have serial communication, but the base model can only be adjusted via RS232 to make minor adjustments to the output. vs the option that allows full frequency adjustment.   I picked up one of these last month, and I remember reading that somewhere...

For my some of test equipment the output voltage was low to use a a reference, and some also need a square vs a sine wave, so that's that next part to make a multiplexer with both square and sine wave outputs...maybe something else to do to yours as well?
« Last Edit: January 13, 2012, 10:30:25 am by Zyvek »
-Z
 

Offline EEVblog

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #19 on: January 13, 2012, 10:30:16 am »
How many hours upon hours have you wasted wrestling with video editors and editing and YouTube and servers and such?  Don't you think your fans would rather see you wrestling with electronic curiosities?  It may be time to start thinking about bringing in an intern who wants to build their experience with these things.  I'm sure the local community college has students eager to work on something.  They might even have access to better editing equipment and software at their lab.

I understand you are having a great time and all but if you want your blog to "scale", letting go of some of these routine task is inevitable.  Not trying to be rude or anything, just rather see you doing electronics instead.   ;D :-[ (can't find a fitting smiley to convey my deference to you in making such a suggestion)

I can't see that happening. Sounds great in theory, but it's just not that practical.
When I edit video I'm also making sure I haven't missed something I want to add, said something dumb, repeated myself, need to add something with a text overlay etc.
At the moment I do that at the same time as I'm editing, and I don't view back afterwards, I just upload when done hoping I've got it right (and I mostly do).
If someone else edited my content, then I'd still have to watch the entire video back and concentrate while doing so. Something wrong - another spin...
So I might as view it while editing the thing myself, it doesn't take that much longer, as I have my workflow pretty well down pat.
I'd likely spend more time interacting with the editor, sending files to them (unless they work on-site), downloading previews etc.

And beside, I like creating my own content, I get a sense of satisfaction even though it can be time consuming and a PITA sometimes.

Get someone else to edit it, and you end up like the Ben Heck show  ;D

It's just like going full time at this. Many people complain about why I'm not churning out a video or two every day now that I magically have another 40 hours a week to work on this full time. It doesn't quite work like that...  ::)

Dave.
« Last Edit: January 13, 2012, 10:37:25 am by EEVblog »
 

Offline mikeselectricstuff

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #20 on: January 13, 2012, 10:47:29 am »
It might be the player. Just lately I've noticed a few videos with the audio badly out of sync (2-3 seconds), from many different uploaders. I can't imagine every case is a problem with the original content, so my bet is the trouble lies at YouTube's end.

Good to know, thanks.

Dave.
One of my recent vids had some de-syncing for a coupel of mins that wasn't showing in the editor so maybe YT have broken something again.
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Offline mikeselectricstuff

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #21 on: January 13, 2012, 11:45:29 am »
Oh dear....
"NOW it is 2008 year .we need some coooooool super supply to enhance the sound quality of your CD Player

As you know most of CD or any other Audio Players Use the OCXO oscillator for  the Frequency Standard.

Ok,the OCXO oscillator just the short stable....why do you try some other Long stable  as your heart of your CD ?
"

http://www.ebay.co.uk/itm/11-2896Mhz-Rubidium-Master-clock-CD-/290273920268?pt=LH_DefaultDomain_0&hash=item4395ac850c


Oh FFS....

"Buy it and claim your atomic energy bragging rights. For those refusing to accept compromises with the audio quality there is the Isochrone 10M - a Rubidium Atomic Reference Generator based on real atomic technology. The 10M is designed specifically to appeal to the most discerning audiophiles and audio professionals. If your goal is to set up your studio for maximum performance, you will certainly appreciate a clocking reference that is a staggering 100,000 times more accurate than the quartz oscillators used in most equipment.
"
http://www.ebay.co.uk/itm/Antelope-Audio-Isochrone-10M-Rubidium-Atomic-Clock-/270809581736?pt=LH_DefaultDomain_0&hash=item3f0d8248a8

Question for the mathematically inclined - how fast would you need to move your head towards the speaker to induce a doppler shift of a similar order of magnitude to that of the error on a Rb standard?
« Last Edit: January 13, 2012, 11:52:14 am by mikeselectricstuff »
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Offline firewalker

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #22 on: January 13, 2012, 11:58:13 am »
He is an amateur. With the right promotion he could sell it more than a new one costs.

Alexander.

Oh dear....
"NOW it is 2008 year .we need some coooooool super supply to enhance the sound quality of your CD Player

As you know most of CD or any other Audio Players Use the OCXO oscillator for  the Frequency Standard.

Ok,the OCXO oscillator just the short stable....why do you try some other Long stable  as your heart of your CD ?
"

http://www.ebay.co.uk/itm/11-2896Mhz-Rubidium-Master-clock-CD-/290273920268?pt=LH_DefaultDomain_0&hash=item4395ac850c


Oh FFS....

"Buy it and claim your atomic energy bragging rights. For those refusing to accept compromises with the audio quality there is the Isochrone 10M - a Rubidium Atomic Reference Generator based on real atomic technology. The 10M is designed specifically to appeal to the most discerning audiophiles and audio professionals. If your goal is to set up your studio for maximum performance, you will certainly appreciate a clocking reference that is a staggering 100,000 times more accurate than the quartz oscillators used in most equipment.
"
http://www.ebay.co.uk/itm/Antelope-Audio-Isochrone-10M-Rubidium-Atomic-Clock-/270809581736?pt=LH_DefaultDomain_0&hash=item3f0d8248a8

Question for the mathematically inclined - how fast would you need to move your head towards the speaker to induce a doppler shift of a similar order of magnitude to that of the error on a Rb standard?
Become a realist, stay a dreamer.

 

Offline Rerouter

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #23 on: January 13, 2012, 12:14:52 pm »
may be wrong but...

say a 1khz signal

the length of the waveform is 1mm, so a 10^-11 error means 10 picometers to exceed the error,
so by moving towards or away from the speaker at more than 10 pico-meters per second, you exeed the error.

not much eh.. :)
 

Offline robrenz

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #24 on: January 13, 2012, 01:55:38 pm »
1kHz = 2.9979e+5 meters wavelength

Offline metalphreak

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #25 on: January 13, 2012, 02:50:41 pm »
I didn't notice any sync issues until I read the comments, then I noticed a very slight lag between the audio and Dave's lips moving. I would say its maybe 50ms or so, nothing really serious.

Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #26 on: January 13, 2012, 08:22:39 pm »
I am trying to work out how much the thing drifts per year measured in time. Datasheet says it has long term stability of 2 x 10^-11. But 2 x 10^-11 of what? 1 hz? 10mHz or whatever the physics pacakage is running at? Or something else?

Thanks.M
 

Offline ejeffrey

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #27 on: January 13, 2012, 09:11:48 pm »
It is a fractional change.  Since it has a 10 MHz output (10^7 Hz), a drift of 10^-11 is a change of 10^-4 Hz.  The 6 GHz internal microwave frequency will change by 0.06 Hz.  If you divide it down to a PPS (1 Hz) signal, that will change by 10^-11 Hz.  Use it to stabilize a frequency synthesizer and the output of the synthesizer will drift by 10^-11 of whatever the operating frequency is.
 

Offline tnt

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #28 on: January 13, 2012, 09:14:29 pm »
It's always a deviation from nominal value.

dev = abs( (f_real - f_nom) / f_nom )

and the absolute frequency doesn't matter ...

Imagine you have a 10 MHz output and a 1 Hz error, then if you derive a 1 GHz frequency from that source then you'll get a 100 Hz error.
 

Offline rf-loop

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #29 on: January 13, 2012, 09:42:13 pm »
I am trying to work out how much the thing drifts per year measured in time. Datasheet says it has long term stability of 2 x 10^-11. But 2 x 10^-11 of what? 1 hz? 10mHz or whatever the physics pacakage is running at? Or something else?

Thanks.M

If 10MHz (10 Mega Hz) have 2x10Exp-11 error, say example it is this amount too fast.
Its frequency is 10 000 000.000 2 Hz. (10.0000000002 MHz)

In rough this stability means error. But "long term stability"  - and I ask "how long" ;)
How about short term..

Then, in what situation. In stabilized outside temperature, pressure, magnetic field etc.

If compare example cheap Efratom LPRO-101. (DATUM LPRO-101) these are factory adjusted inside +-5x10exp-11  error, same accuracy what example I have done as I have sometimes calibrated these to someone.) It means that frequency is (with given enviroment variables) between 9.9999999995 - 10.0000000005 MHz.
Of course if same error  in one Hz. It means  0.99999999995 - 1.00000000005Hz.
Now it can ask how many seconds need that it have (accumulated) one second error.

But in practice year level drift is more than +-2x10exp-11.

I have checked tens of LPRO-101 and some these FEI models also after they have take out from active original use.

After different time of use and diffrent sometimes also very hard enviroments used. Then I have checked (before my adjustments) they have all been typically well  inside +-10x10exp-10 error window. (10MHz under 10mHz error) Mostly drifted to up some mHz. (why?) No one can exactly tell how long they have used and how long after any calibration so this do not give much of information.
Also most of Rb need be 48-72 hour or even more on before check. (but well.. <30 minutes they are typically very near real working freq)


C-field setting may also drift.  (It is sensitive to magnetic field strenght and direction and it is also method for adjust it) Even earth magnetic field affect it.

Rb physic package have many mechanism for drift.   It is NOT primary standard as example Cesium or Hydrogen maser.
If practice and theory is not equal it tells that used application of theory  is wrong or the theory itself is wrong.
It is much easier to think an apple fall to the ground than to think that the earth and the apple will begin to move toward each other and collide.
 

Offline don.r

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #30 on: January 14, 2012, 02:07:36 am »
What is the lifetime of the lamp and is there any way to measure the life left after purchase? This would be my biggest concern. Considering you can get an Thunderbolt or equivalent for about $150, I'm not completely sold on these.
« Last Edit: January 14, 2012, 07:06:18 am by don.r »
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Offline wkb

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #31 on: January 14, 2012, 02:16:02 am »

If compare example cheap Efratom LPRO-101. (DATUM LPRO-101) these are factory adjusted inside +-5x10exp-11  error, same accuracy what example I have done as I have sometimes calibrated these to someone.) It means that frequency is (with given enviroment variables) between 9.9999999995 - 10.0000000005 MHz.


What do you use to calibrate the Rb units?  Curious here..
 

Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #32 on: January 14, 2012, 07:02:13 am »
So, how many years can i expect before it is off by 1 sec? It's off by 2x10^-11 every year.  I it correct that it will be off by 1 sec every (2x10^11)/2 yrs? Circa 100 000 000 000yrs?

Is my math wrong?M
« Last Edit: January 14, 2012, 10:59:54 am by king.oslo »
 

Offline ejeffrey

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #33 on: January 14, 2012, 07:30:44 am »
What do you use to calibrate the Rb units?  Curious here..

You can reference them to a GPS pulse-per-second source which has better stability over time periods greater than a day or so.  I am not sure what the mechanism for aging is, certainly the rubidium atoms themselves don't change.  Perhaps it is a drift in the offset voltage of the lock-in amplifiers phase detector, or some non-linearity in the dither signal applied to the microwave frequency.

SRS has some more information about how these things work: http://www.thinksrs.com/products/PRS10.htm.  They sell both the modules like Dave shows here, and also complete instruments with power supplies and multiple outputs for synchronizing a whole rack full of equipment.
 

Offline Blue

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #34 on: January 14, 2012, 10:52:29 am »
The Stanford Research Systems make nice products. I've got a lock-in amplifier from them.
But I do not understand their price politics and I hate them for that: International buyers have to pay 10% more that US customers  >:(.

Why? Do they hate foreigners so much that they have to screw them?
 

Offline rf-loop

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #35 on: January 16, 2012, 12:37:22 am »

If compare example cheap Efratom LPRO-101. (DATUM LPRO-101) these are factory adjusted inside +-5x10exp-11  error, same accuracy what example I have done as I have sometimes calibrated these to someone.) It means that frequency is (with given enviroment variables) between 9.9999999995 - 10.0000000005 MHz.


What do you use to calibrate the Rb units?  Curious here..

Long time averagin method with two  HP Z3801  one HP/Symmetricom 58503A (it is nearly same as Z3801)
and  HP53131A  for statistical analyze so that I can think if can trust or not. Also I can follow with some poor Trimble Thunderbolt and 
With careful long time method this can easy go to this accuracy. If I see some disturbance in stability I just put this follow to garbage and take agen.  (of course also Rb under test/adjust need control with temperature. Normally I watch this plate temp where Rb under test is sitting.)
Of course Rb's under test/adjust need also "burn in" after maybe long time not powered. There are some small drifting maybe after long time not used. Minimum is 3-4 days. Rb have not so big this effect but example OCXO adjustment is more difficult. Just becouse ageing curve and maybe high retract if long time not used. Also it is littlebit unknown how it go agen to follow its nominal ageing curve. Every OCXO is just different.

About Rb lamp. Mostly it is not real problem if so not use these oldest Ball Efratom models.
I do not know who and why have started this Rb lamp paranoic.
I have not seen real lamp fail in example LPRO-101. But many fails what "looks like" lamp fail.
I littlebit think this lamp paranoic come from history when Rb lamps was littlebit different and also units price was high.

Today there is there mass produced Rb's and...
... just if cheap shirt come dirty buy new.
If practice and theory is not equal it tells that used application of theory  is wrong or the theory itself is wrong.
It is much easier to think an apple fall to the ground than to think that the earth and the apple will begin to move toward each other and collide.
 

Offline JBeale

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Re: Eevblog #235 - Rubidium Frequency Standard FE-5860A FAQ
« Reply #36 on: January 23, 2012, 03:59:54 pm »
I started a FAQ about this particular model, the FE-5860A (to be more precise, the cheaper of the versions currently available on the auction sites, since FEI made so many different variants with the same model number.)

http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5860a_faq

List of FAQ topics:

    FE-5680A Rubidium Frequency Standard FAQ
        What is a FE-5680A and why would I want one?
        Useful Links
        Parameter Specifications
        Connector Pinout
        Why doesn't the C-field adjustment trimpot through the hole in the side do anything?
        What is the range of frequency adjustment via RS-232 commands?
        What if my 5680A output does not lock up after several minutes?
        Can I get a square wave 10 MHz output instead of a sine wave?
        How can I get a 1 PPS output?
        What is the typical drift with temperature (tempco)?
        Long Term Frequency stability
        Input Voltage Requirements (official spec is 15 - 18 volts DC)
        Is a Rb frequency standard sensitive to external magnetic fields?
        Mechanical Dimensions
        Electronic Parts
        Undocumented RS-232 commands

 

Offline JBeale

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Re: Eevblog #235 - Rubidium Frequency Standard - comparing to GPS
« Reply #37 on: January 23, 2012, 04:29:02 pm »
You can reference them to a GPS pulse-per-second source which has better stability over time periods greater than a day or so. [...]
In the long term, certainly GPS has better accuracy, but not necessarily in one day. Just for reference: at my location (poor sky visibility, and restrictions on antenna mounting) the only GPS I have that works, has as much as 400 ns of drift relative to a stable reference, at any given time (due to multipath issues I assume). Anyway, 400 ns in 24 hours is a relative stability of 5E-12, and at least one report from a surplus FE-5860A I've seen is showing less than 1E-12 drift after 8 weeks (though some units are worse).  If I want to be conservative and have my reference stability 10x better than the drift I'm measuring, I'd need to measure against GPS for over a month to be confident of a drift measurement at the 1E-12 level.
 

Offline wkb

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Re: Eevblog #235 - Rubidium Frequency Standard FE-5860A FAQ
« Reply #38 on: January 23, 2012, 06:14:43 pm »
I started a FAQ about this particular model, the FE-5860A (to be more precise, the cheaper of the versions currently available on the auction sites, since FEI made so many different variants with the same model number.)

http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5860a_faq


Thanks!  I have a unit on its way from HKO so this might come in handy.  Been collecting URLs myself too but the centralised location of the FAQ is sure nice to have.
 

Offline mikeselectricstuff

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #39 on: February 02, 2012, 03:48:30 am »
Extreme teardown of the physics package:
Youtube channel:Taking wierd stuff apart. Very apart.
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Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #40 on: February 02, 2012, 04:36:52 am »
mikeselectricstuff, you creative genius!

Keep them coming. Next do a atomic battery teardown!  ;D M
 

Offline Blue

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #41 on: February 02, 2012, 05:34:13 am »
 8) Cool

can you repeat it with the lamp underwater instead of above the waterline?  :)
 

Offline JBeale

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #42 on: February 02, 2012, 05:53:40 am »
Why does this come with an OCXO?

The "free gift" OCXO has nothing to do with the FE-5680A, and the odd frequency is not particularly useful for anything (unless you run your own cell base station, it's related to a CDMA sampling frequency I think). The guess is he just had some extra parts no one wanted, and wanted to sweeten the deal and distinguish from the several other sellers offering the same 5680 unit.
 

Offline EEVblog

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #43 on: February 02, 2012, 08:46:15 am »
Extreme teardown of the physics package:

Excellent update Mike.
How did you get the close up shot of the bulb?
What camera are you using?, and did you shot the video under a magnifying lamp or something?
One of things I'm disappointed at with my Canon HF G10 camera is it's lack of ability to do good macro closeups.

Dave.
 

Offline mikeselectricstuff

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #44 on: February 02, 2012, 09:06:05 am »
Extreme teardown of the physics package:

Excellent update Mike.
How did you get the close up shot of the bulb?
What camera are you using?, and did you shot the video under a magnifying lamp or something?
One of things I'm disappointed at with my Canon HF G10 camera is it's lack of ability to do good macro closeups.

Dave.
It's a Panasonic HDC-SD10 camcorder (£70 on ebay bought as faulty & fixed!).
It will focus close enough to get a 20mm wide object full-screen.
I think you can get macro add-on lenses for some camcorders
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Offline EEVblog

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #45 on: February 02, 2012, 09:39:14 am »
It's a Panasonic HDC-SD10 camcorder (£70 on ebay bought as faulty & fixed!).
It will focus close enough to get a 20mm wide object full-screen.
I think you can get macro add-on lenses for some camcorders

Thanks.
Yeah, have to look into a good macro lens for the Canon.
Bound to be one given the standard lens thread size.

Dave.
 

Online BravoV

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #46 on: February 02, 2012, 02:30:03 pm »
Thanks a lot Mike, really an amazing extreme teardown, especially the exploding rubidium bulb !

Just make sure you don't drink that RbOH solution by accident !  ;D
 

Offline jahonen

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #47 on: February 02, 2012, 07:54:06 pm »
Measured warm-up transient from my FE-5680A.

I'm wondering if the initial sweep should be symmetrical around 10 MHz or not.

Regards,
Janne
 

Offline KD0CAC John

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #48 on: February 03, 2012, 05:01:43 am »
Mike ,
You mentioned getting some more rubidium , when do we get to see the next water test ? :)
I would say that there was a much larger reaction to the metal than breaking the bulb , because of the sloshing of the water .
Next time I would suggest holding the bulb under water and then using a punch / etc. to just tap on glass while being held steady underwater , just a slight tap on glass .

If is doesn't explode , then its only half as fun :)
 

Offline firewalker

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #49 on: February 03, 2012, 05:38:28 am »
Don't expect to see something at all. The amount of Rubidium inside the lamp is minimal.

Alexander.

Become a realist, stay a dreamer.

 

Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #50 on: February 06, 2012, 04:38:29 am »
I am trying to work out how long before the clock deviates from real time by 1 sec.

Please, will somebody who is knowledgeable check my math? This is my attempt.

Clock starts at 10MHz. The drift is 2E-9. So the drift coeffecient is 1.000000002. So I make an intergral to work out how long the clock needs to accumulate 10MHz of drift.

What do you think? Thanks!!! :)
« Last Edit: February 06, 2012, 04:46:06 am by king.oslo »
 

Offline jahonen

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #51 on: February 06, 2012, 04:45:37 am »
I am trying to work out how long before the clock deviates from real time by 1 sec.

Please, will somebody who is knowledgeable check my math? This is my attempt.

Clock starts at 10MHz. The drift is 2E-9. So the coeffecient is 1.000000002.

Thanks!!! :)

I think the deviation is simply x*(x/(365*24*60*60))*2e-9 = 1, where x is elapsed time in seconds and thus solving for x we get 1.2557e8 seconds which is equivalent to about 4 years. That is assuming that the drift is constant for all t.

Regards,
Janne
« Last Edit: February 06, 2012, 04:56:20 am by jahonen »
 

Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #52 on: February 06, 2012, 04:48:29 am »
I am trying to work out how long before the clock deviates from real time by 1 sec.

Please, will somebody who is knowledgeable check my math? This is my attempt.

Clock starts at 10MHz. The drift is 2E-9. So the coeffecient is 1.000000002.

Thanks!!! :)

I think the deviation is simply x*2e-9 = 1, where x is elapsed time in seconds and thus solving for x we get 0.5e9 seconds which is equivalent to about 15.8 years.

Regards,
Janne

What makes you think so?

Datasheet says 2E-9 drift/year. That is from nominal value? Nominal value is 10MHz.M
 

Offline jahonen

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #53 on: February 06, 2012, 04:56:56 am »
Sorry, corrected a bit previous post on second thought.

Regards,
Janne
 

Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #54 on: February 06, 2012, 05:04:10 am »
Janne:

Quote
DRIFT             2 x 10-9/year

What do you think this means? I understand you think this is a measure of time, not frequency. Is that correct?M
« Last Edit: February 06, 2012, 05:21:25 am by king.oslo »
 

Offline jahonen

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #55 on: February 06, 2012, 05:24:10 am »
I think it means that the frequency may drift 2e-9 per year relative to initial value. So in one year, one could expect the frequency to be between 10 MHz*(1-2e-9) and 10 MHz*(1+2e-9), if it is initially exactly 10 MHz. So the drift is not necessarily constant or in same direction. That is my understanding.

Regards,
Janne
 

alm

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #56 on: February 06, 2012, 05:42:02 am »
I would not expect drift to be constant over time. Aging is a stochastic process (cf diffusion) that will slow down over time, so drift in the first 24h after manufacturing is probably much larger than 24h drift a few years later. A random OCXO (first data sheet I found) is specified as < 5e-10/24h, <1e-8/month and <7.5e-8/year. The same data sheet also states that aging will decrease substantially after the first six months. The difference with a diffusion process is that there may be some systematic contribution, for example degradation of the lamp in the case of rubidium.
 

Offline IanB

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #57 on: February 06, 2012, 05:42:07 am »
What do you think this means? I understand you think this is a measure of time, not frequency. Is that correct?

For small deviations in the order of 1e-9, frequency and time are effectively interchangeable. So if the frequency was off by 1e-9 then the length of a second would be off by 1e-9 also. Which means it would take 1e9 seconds to accumulate a one second error. Which is 280,000 hours, or 11,500 days, or 32 years.

Ha, I think I need to get one of these to use as a time base for a clock. I can make a clock that never drifts  :)
I'm not an EE--what am I doing here?
 

Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #58 on: February 06, 2012, 05:53:49 am »
Ha, I think I need to get one of these to use as a time base for a clock. I can make a clock that never drifts  :)

Yeah. If the train leave a second early, you know whose evaluation to trust ;)

Janne says 4 yrs. IanB says 32 yrs, I say 31622. What should we do?M
 

Offline jahonen

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #59 on: February 06, 2012, 06:00:22 am »
Tip 2 of this Agilent application note might be relevant:

http://www.home.agilent.com/agilent/editorial.jspx?cc=FI&lc=fin&ckey=505277&nid=-33788.0.00&id=505277

I think that the 4 year figure is pretty much surely pessimistic since the drift will be probably less after 1 year (if rubidium standard is kept continuously on), like alm said.

Regards,
Janne
 

Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #60 on: February 06, 2012, 06:50:30 am »
I think we are all wrong.

I think a good definite integral (0, ) is:

 (10*((1+(6.341154090044388078630310716550412175015852885E-17))^x))-10.

This will add the annual drift at each second and add each second of drift to eachother.

Does anyone know of tools capable of calculating this? It seems wolframalpha isn't able to ;)

Thanks.M
« Last Edit: February 06, 2012, 06:59:10 am by king.oslo »
 

Offline IanB

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #61 on: February 06, 2012, 06:52:45 am »
I think we are all wrong.

I think a good definite integral (0, ) is:

 (10*((1+(6.341154090044388078630310716550412175015852885E-17))^x))-10.

This will add the annual drift at each second and add each second of drift to eachother.

Does anyone know of tools capable of calculating this? It seems wolframalpha isn't able to.

Thanks.M

I think you are pulling our legs. Maybe you need to add a smiley, or people won't get the joke  ;)
I'm not an EE--what am I doing here?
 

Offline Rufus

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #62 on: February 06, 2012, 07:06:43 am »
Ha, I think I need to get one of these to use as a time base for a clock. I can make a clock that never drifts  :)

Yeah. If the train leave a second early, you know whose evaluation to trust ;)

Janne says 4 yrs. IanB says 32 yrs, I say 31622. What should we do?M

And I say 5.63 years.

Assuming worse case drift in the same direction of 2E-9 per year.

Error at the end of T years is T * 2E-9

Average error over a period of T years is T * 2E-9 / 2

The error for 1 second in T years is 1 / (T * 365 * 24 * 60 * 60)

That equality gives T^2 = 1 / (365 * 24 * 60 * 60 * (2E-9  / 2))

my calculator tells me T is 5.63 years.
 

Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #63 on: February 06, 2012, 10:02:06 am »
I did the calculation I suggested at the top of the page. I got to 5.631501903 years. Rufus, my result resonates with yours.

I hope we are being very pessimistic here. 5.63 yrs isn't that great.

Thanks.

Kind regards,
Marius
 

Offline IanB

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #64 on: February 06, 2012, 10:10:37 am »
5.63 yrs isn't that great

Do you have any other clocks that accurate?

Anyway, that is a pessimistic estimate on the assumption the frequency drifts linearly by 2e-9 every year. Most likely the drift is not linear and after the device has "burned in" for a year or so it will be much more stable.
I'm not an EE--what am I doing here?
 

Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #65 on: February 06, 2012, 10:27:10 am »
5.63 yrs isn't that great

Do you have any other clocks that accurate?

Haha! IanB. You are wonderful, man! I love your comments.

No I don't.

The reason I am disappointment is because I'd like one of those atomic clocks that deviate 1sec in 30 million years.

I will have to make a farm of these units, and monitor their drift relative to eachother and relative to another standard.

Thank you for your time.

Kind regards,
Marius
 

Offline amspire

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #66 on: February 06, 2012, 10:48:18 am »
I have a really big problem since I live at an altitude of 1100 meters. Thanks to relativity, time goes much quicker for me then all you lowlanders - about 1 part in 10-13 times faster.

So do I set my clock to keep in sync with sea level clocks, which means my clock is actually running slow, or do I set it correctly which means my clock will always be gaining time on the sea level clocks. If I set my local clock deliberately slow, then the error filters through to everything else that is time related, like the measurement of capacitance. I hate buying a 1nF capacitor from Jaycar, only to find that when I measure it at home, it only reads as 0.99999999999987 nF.

Richard
« Last Edit: February 06, 2012, 10:55:07 am by amspire »
 

Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #67 on: February 06, 2012, 11:03:21 am »
I have a really big problem ...

I love it man! ;D M
 

Online BravoV

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #68 on: February 06, 2012, 11:44:27 am »
I hate buying a 1nF capacitor from Jaycar, only to find that when I measure it at home, it only reads as 0.99999999999987 nF.

Wow.. that Jaycar's cap is really good, what part number is that ? :D  j/k

Btw Richard, I heard you're planning to move all your measurement stuffs upstairs at 1103 meters ? I guess its time to do some re-adjustment again.  :-[
 

Offline amspire

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #69 on: February 06, 2012, 11:58:35 am »
I gather the time dilution difference between shelves on a workbench is measurable - if you work at the American NIST labs. So your frequency counter positioned on the shelf about your signal generator is running about one part in 4 x 10-17 faster then the generator.
 

Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #70 on: February 06, 2012, 12:05:20 pm »
Richard, you must compensate for the gravitational fluctuations caused by passing birds or insects.M
« Last Edit: February 06, 2012, 12:08:10 pm by king.oslo »
 

Offline amspire

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #71 on: February 06, 2012, 12:08:56 pm »
Richard, you must compensate for the gravitational fluctuations of any passing birds or insects.M
Don't tell me. It is a waste of time even trying to run my NE555 oscillator when the birds are flying around.
 

Offline gxti

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #72 on: February 07, 2012, 01:23:40 pm »
The original video blog got me thinking about buying one of these magnificent devices, but then I talked myself out of it because I really don't need more useless shit. Now this thread keeps taunting me. Inviting me. Oh and will you look at that, I can do even better -- multiple used Trimble Thunderbolt GPSDO on ebay for 100-150USD. Oh, dear. The lure of the Time Nerd is strong :(
 

Offline amspire

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #73 on: February 07, 2012, 01:51:29 pm »
The original video blog got me thinking about buying one of these magnificent devices, but then I talked myself out of it because I really don't need more useless shit. Now this thread keeps taunting me. Inviting me. Oh and will you look at that, I can do even better -- multiple used Trimble Thunderbolt GPSDO on ebay for 100-150USD. Oh, dear. The lure of the Time Nerd is strong :(

Every now and then I think about adding a circuit to use GPS to improve my rubidium oscillator from 1 part in 10-9 to one part in 10-12, but then I have to stop myself and ask "Why?".

To even see a one cycle drift at 10MHz at that precision will take over a day. It is a million times better accuracy then most crystal oscillators in test equipment can manage anyway. It would probably make me think that all my other equipment is lousy.

Next time you think of it, just seek emergency medical help.

Richard.
 

Offline joelby

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #74 on: February 07, 2012, 02:05:11 pm »
I'm using GPS to improve the stability of an OCXO (for distributed network synchronisation) and was hoping to compare that to my rubidium oscillator!

It would be far cheaper and easier to just use rubidium oscillators instead of the GPS/OCXO combo, if it weren't for the high power consumption and the chance that the supply could dry up at any moment :)
 

Offline Rerouter

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #75 on: February 07, 2012, 05:07:49 pm »
amspire, because you are higher up, time actually would move slower for you :), but thats only from the point of referance of someone looking at you from the ground,

i wonder what a gps corrected rubidium reference would be like... near atomic clock.. or just another magnitude,
 

Offline king.oslo

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #76 on: February 07, 2012, 05:29:12 pm »
Rerouter, you are too clever for us man ;)

Yet Richard has a big problem. He will still arrive late to meetings. And whenever he phones somebody, it will be late. I think he needs an altitude- and space-based-interferometer-corrected-clock. I hear NASA is building one. Perhaps he can get a subscription? ;)

"Pick one up"
« Last Edit: February 07, 2012, 05:41:34 pm by king.oslo »
 

Offline amspire

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #77 on: February 07, 2012, 06:11:47 pm »
amspire, because you are higher up, time actually would move slower for you :), but thats only from the point of referance of someone looking at you from the ground,
I got the sign wrong? Are you telling me that when I thought I wave been arriving at meetings early, I have actually been turning up late by at least a few picoseconds?

I am devastated.
 

Offline TerminalJack505

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #78 on: February 28, 2012, 02:41:09 pm »
I hope that those of you who planned on getting one (or more) of these already have.  The ebay sellers have doubled their prices since Dave's video first came out.  I remember seeing several sellers charging just 35 or 40 bucks.  Those same sellers are now charging $80.  You can look at the sell history to confirm this.
 

Offline grumpydoc

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #79 on: February 28, 2012, 08:14:39 pm »
Yes, it's pretty annoying as I was going to pick one up. Think I'll wait and see if they drop back down again.
 

Offline wkb

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #80 on: February 29, 2012, 05:55:59 am »
I hope that those of you who planned on getting one (or more) of these already have.  The ebay sellers have doubled their prices since Dave's video first came out.  I remember seeing several sellers charging just 35 or 40 bucks.  Those same sellers are now charging $80.  You can look at the sell history to confirm this.

Holy cow... Just checked that, I bought my 2nd Rb from the seller now offering one http://www.ebay.com/itm/250967728839?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_2555wt_1210.

Small difference: I paid $ 35,88 and $ 9,99 shipping to NL.

Other than the price increase, I do recommend this seller, very friendly contact etc.
 

Offline McMonster

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #81 on: February 29, 2012, 06:51:26 am »
Hopefully by the time I really decide it's worth (read as "it'll make a significant difference for some application I'll be working on") the prices will greatly drop so I could get one.

It's interesting how much influence EEVblog has on the hobby market. Parts' and devices' price, availability on online auctions and hobby-oriented buisnesses, interest in EEVblog's products like uCurrent and uSupply etc.
 

Offline Bored@Work

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #82 on: February 29, 2012, 06:59:46 am »
Just wait until all the kids who now bought one "because Dave said so" will resell them, because they have no use for it.
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Offline TerminalJack505

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #83 on: February 29, 2012, 07:12:07 am »
Just wait until all the kids who now bought one "because Dave said so" will resell them, because they have no use for it.

LOL.  I was nearly one of those 'kids.'  I could almost justify (in my own mind) buying one when they were $35.  Now...not so much.

I hope Dave is getting some kind of kickback from these guys.
 

Offline McMonster

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #84 on: February 29, 2012, 07:37:11 am »
Just wait until all the kids who now bought one "because Dave said so" will resell them, because they have no use for it.

I just hope they'll ship to Poland. ;)
 

Offline scopeman

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #85 on: March 06, 2012, 03:36:14 pm »
I offered a seller 38.00 each if he would sell me 10 units. He agreed then reneged on the deal only promising to sell me 5 units at that price, claiming that he had "less stock" than he said that he had. I got my 5 but I'll bet that he still has tons of them.

Mine has the standard pin out (+15 Pin 1, Gnd Pin2, Lock Pin 3, +5V Pin4, Gnd Pin 5, 1pps Pin 6,
Pin 7 10MHz, Pin 8 RX IN, Pin 9 TX Out ) and the RS-232 that I can trace the input RX data signal with a scope  all the way to the control micro but I can not get the unit to respond to serial commands.

Anyone who has any ideas please pipe up!

Thanks,

Sam
 

Offline wkb

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #86 on: March 06, 2012, 10:20:25 pm »
I offered a seller 38.00 each if he would sell me 10 units. He agreed then reneged on the deal only promising to sell me 5 units at that price, claiming that he had "less stock" than he said that he had. I got my 5 but I'll bet that he still has tons of them.

Mine has the standard pin out (+15 Pin 1, Gnd Pin2, Lock Pin 3, +5V Pin4, Gnd Pin 5, 1pps Pin 6,
Pin 7 10MHz, Pin 8 RX IN, Pin 9 TX Out ) and the RS-232 that I can trace the input RX data signal with a scope  all the way to the control micro but I can not get the unit to respond to serial commands.

Anyone who has any ideas please pipe up!

Thanks,

Sam

Serial commands as in setting the output frequency to something radically different from 10MHz, like 5MHz for example? 

Sounds like you have the non-settable variant (like I do) which only allows you to adjust the 10.0000000 <whatever>MHz in the mHz range.  The Rb units look the same but have different electronics.  The el-cheapo like you seem to have and I definitely have do not have the wide-range DDS with serial interface control.  The el-cheapo's do not respond to the commands the wide-range DDS units do.

Go and Google and you will find tons of sites explaining this.
 

Offline wkb

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #87 on: March 10, 2012, 12:22:14 am »
While looking into GPS NTP reference appliances for a data center I just stumbled on this one:

http://www.symmetricom.com/media/files/downloads/product-datasheets/PB_SA_32m.pdf

Really neat if you ask me...
 

Offline @rt

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #88 on: May 16, 2015, 02:01:52 am »
Hi Guys,
I know it’s an old topic, but I was watching this video on Rb standard, and the accuracy of a range of crystal oscillators.
Also another video about a program Dave wrote to test drift of crystal oscillators for some underwater project.

I find this difficult to relate to practical terms because how would you know if a crystal would drift one way or another?
I know there are watch crystals made so you can count till the overflow of a 16 bit timer, and that’s a second,
and those are probably cut more accurate.

Say you had a typical even MHz frequency crystal say 4 - 20 MHz, that was TTL buffered and divided down so you
could flash an LED at 1 Hz, and you also had a Rb frequency standard or GPS PPS output connected to an LED right next
to the 1 Hz crystal LED, and they were aligned perfectly to the clock cycle.
How long would it take before you could notice any drift between the two LEDs just from a Human looking at them?

 

Offline Dave

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #89 on: May 18, 2015, 11:25:21 am »
I find this difficult to relate to practical terms because how would you know if a crystal would drift one way or another?
You find a much more stable and accurate frequency source and use it as a reference for your frequency counter. You connect the observed oscillator to the input and log the measured values.
That would be one way to do it.

I know there are watch crystals made so you can count till the overflow of a 16 bit timer, and that’s a second,
and those are probably cut more accurate.
Nope. Watch crystals are usually 32.768kHz, so 2^15 Hz.

Say you had a typical even MHz frequency crystal say 4 - 20 MHz, that was TTL buffered and divided down so you
could flash an LED at 1 Hz, and you also had a Rb frequency standard or GPS PPS output connected to an LED right next
to the 1 Hz crystal LED, and they were aligned perfectly to the clock cycle.
How long would it take before you could notice any drift between the two LEDs just from a Human looking at them?
Good crystals usually have about 20 ppm accuracy. Assuming you would be able to notice when LEDs are at least 1/20 of a second apart and assuming the worst case scenario (crystal being off by 20ppm), it would take 2500 seconds for you to notice it (roughly 42 minutes). Of course, varying temperature, vibration, shock and shitty crystals might give significantly worse results.

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<fellbuendel> if you knew, you wouldn't be using it
 

Offline max666

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #90 on: May 18, 2015, 12:09:27 pm »
While looking into GPS NTP reference appliances for a data center I just stumbled on this one:

http://www.symmetricom.com/media/files/downloads/product-datasheets/PB_SA_32m.pdf

Really neat if you ask me...
Link doesn't work, and man does that site annoy me.
 

Online Vgkid

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #91 on: May 18, 2015, 12:29:58 pm »
Google symmetricom sa.32
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Offline max666

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Re: Eevblog #235 - Rubidium Frequency Standard
« Reply #92 on: May 18, 2015, 01:10:41 pm »
Google symmetricom sa.32
Thanks, that helped.

I was looking if an enthusiast could buy them, but the only thing I found was this (I'm probably doing it wrong):
http://www.ebay.com/itm/Symmetricom-SA-31m-Miniature-Rubidium-Oscillator-090-44310-01-W-Interface-Cables-/231560038309?pt=LH_DefaultDomain_0&hash=item35ea0dc7a5
I wonder how much they cost new.
 


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