Author Topic: EEVblog #456 - CSIRO Rubidium Frequency Standard  (Read 34156 times)

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EEVblog #456 - CSIRO Rubidium Frequency Standard
« on: April 19, 2013, 12:07:53 am »
Dave uses his CSIRO National Measurement Institute rubidium frequency standard to calibrate and adjust his Agilent 53131A frequency counter.
With bonus teardowns.



 

Offline mswhin63

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #1 on: April 19, 2013, 12:19:51 am »
I love those racks, reminds me of the old railway days working on the radio and signalling systems  :-+ :-+ :-+
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Offline olsenn

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #2 on: April 19, 2013, 12:40:38 am »
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?
 

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #3 on: April 19, 2013, 12:49:31 am »
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.

Yes, that's the idea of course.
The stock oscillators are crap, it'll drift more than the SS Minnow

Quote
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?

You won't see any difference with 10 digits
 

Offline free_electron

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #4 on: April 19, 2013, 02:01:46 am »
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 !
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Offline lowimpedance

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #5 on: April 19, 2013, 03:32:07 am »
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
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Offline tylerl

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #6 on: April 19, 2013, 05:03:01 am »
According to the manual 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?
 

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #7 on: April 19, 2013, 05:08:30 am »
According to the manual 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?

Why? Because I could.
 

Offline chickenHeadKnob

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #8 on: April 19, 2013, 05:17:54 am »
Hello All

When 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.
 
 

Offline ddavidebor

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EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #9 on: April 19, 2013, 05:24:17 am »
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.

Yes, that's the idea of course.
The stock oscillators are crap, it'll drift more than the SS Minnow

Quote
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?

You won't see any difference with 10 digits

You need to use a scope and measure with the watch the time the two signal need for drift of X degree

And make some calculation, don't know what calculation
Davide Bortolami,
Fermium LTD
 

Offline Bored@Work

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #10 on: April 19, 2013, 06:05:52 am »
Hello All

When 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.

Yes, 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).
« Last Edit: April 19, 2013, 06:07:36 am by Bored@Work »
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Offline Huluvu

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #11 on: April 19, 2013, 06:12:57 am »
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.


@Dave   can you please look at the Delta PSU board for some PN (maybe I can check in SAP ......)    ::)

"Yeah, but no, but yeah, but no..."
 

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #12 on: April 19, 2013, 06:35:37 am »
When 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.

Yes, the Stanford unit specifies a guaranteed 20 year life.
 

Offline Ed.Kloonk

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #13 on: April 19, 2013, 09:03:04 am »
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.

Yes, that's the idea of course.
The stock oscillators are crap, it'll drift more than the SS Minnow

[chuckle]   ;D

 

Offline grumpydoc

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #14 on: April 19, 2013, 12:27:13 pm »
Quote
The stock oscillators are crap, it'll drift more than the SS Minnow


They'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.  :scared:

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 poor :)

I suspect that these were intended to be used with the Rubidium standard rather than the inbuilt oscillator.
 

Online firewalker

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #15 on: April 19, 2013, 12:36:44 pm »
Would it worth the trouble to replace that trim cap with something more "trimable"?

Alexander.
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Offline c4757p

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #16 on: April 19, 2013, 12:46:16 pm »
I suspect that these were intended to be used with the Rubidium standard rather than the inbuilt oscillator.

Yeah, 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...  :-//
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Offline grumpydoc

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #17 on: April 19, 2013, 12:48:08 pm »
Quote
Would it worth the trouble to replace that trim cap with something more "trimable"?

Probably 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 :)
 

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #18 on: April 19, 2013, 12:58:41 pm »
Yes the stock oscillator is just a toy in such a good counter. They expect you to at least spring for the oven osc.
 

Offline Ed.Kloonk

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #19 on: April 19, 2013, 01:03:52 pm »
Could you feed one of the rb outputs to a clock input on the counter?

 

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #20 on: April 19, 2013, 01:16:37 pm »
Could you feed one of the rb outputs to a clock input on the counter?

Of course, that's why all counters have external clock inputs.
 

Offline Ed.Kloonk

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #21 on: April 19, 2013, 01:17:44 pm »
Could you feed one of the rb outputs to a clock input on the counter?

Of course, that's why all counters have external clock inputs.

 :palm:


Boozy tonite mate sorry.

 

Offline bingo600

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #22 on: April 19, 2013, 01:33:52 pm »
Daummmm .... Dave
This is "cheating" & Not fair  :'( :'(

Did you get both the RB & Freq Counter for $260  :-+

A used PRS10 is 750+ US$ on the 'Bay ... alone

Send it to me for "Looooooonnnngggg time" calibration testing ... 10 years or so ...
I have the GPS antenna for it  ;)


/Bingo

 

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #23 on: April 19, 2013, 01:39:35 pm »
Did you get both the RB & Freq Counter for $260  :-+

Yep, both, plus the industrial PC, plus the APC PSU and batt.

Quote
A used PRS10 is 750+ US$ on the 'Bay ... alone

Yes, they are not cheap. I could sell both for a big profit, but the PRS10 is just so darn nice...  ;D
I had an FS725 once, but sold that.
 

Offline kyndal

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #24 on: April 19, 2013, 02:04:16 pm »
if i had a GPS disciplined, rubidium frequency standard on hand
i 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... circuit
and feed it the 10mhz reference...

finally go cook some eggs up with a only a few ppm's worth of precision and consistency

challenge posted!.    :-/O


haha..


/Kyndal
 

Offline ddavidebor

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EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #25 on: April 19, 2013, 02:12:50 pm »
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?
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Offline ddavidebor

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EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #26 on: April 19, 2013, 02:14:18 pm »
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?
Davide Bortolami,
Fermium LTD
 

Offline Ed.Kloonk

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #27 on: April 19, 2013, 02:16:57 pm »
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?

The clear, shiny coating that covers all components on the board.

 

Offline Ed.Kloonk

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #28 on: April 19, 2013, 02:20:13 pm »
ddavidebor,

When you say

Oh, i can't understand a word.


or

I 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.
 :-+

« Last Edit: April 19, 2013, 02:22:23 pm by Ed.Kloonk »
 

Offline bingo600

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #29 on: April 19, 2013, 02:21:08 pm »
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?

Yes 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
 

Offline tinhead

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #30 on: April 19, 2013, 02:21:52 pm »
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?

http://en.wikipedia.org/wiki/Conformal_coating
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Offline free_electron

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #31 on: April 19, 2013, 02:54:52 pm »

I suspect that these were intended to be used with the Rubidium standard rather than the inbuilt oscillator.

The 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.

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Offline Zad

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #32 on: April 19, 2013, 04:01:33 pm »
Daummmm .... Dave
A used PRS10 is 750+ US$ on the 'Bay ... alone


You are looking in the wrong place then. They have been going recently for $400

www.ebay.co.uk/itm/SRS-STANFORD-RESEARCH-SYSTEM-PRS10-RUBIDIUM-FREQUENCY-STANDARD-/130891002337

Offline gxti

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #33 on: April 19, 2013, 05:45:31 pm »
When 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.
Cesium 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.
 

Offline bingo600

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #34 on: April 19, 2013, 09:19:51 pm »
Daummmm .... Dave
A used PRS10 is 750+ US$ on the 'Bay ... alone


You are looking in the wrong place then. They have been going recently for $400

www.ebay.co.uk/itm/SRS-STANFORD-RESEARCH-SYSTEM-PRS10-RUBIDIUM-FREQUENCY-STANDARD-/130891002337

Hmmm ... I hope there are more to come ...

Thnx

/Bingo
 

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #35 on: April 20, 2013, 09:03:26 am »
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.
 

Offline jpb

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #36 on: April 20, 2013, 09:26:25 am »
if i had a GPS disciplined, rubidium frequency standard on hand
i 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... circuit
and feed it the 10mhz reference...

finally go cook some eggs up with a only a few ppm's worth of precision and consistency

challenge posted!.    :-/O



haha..


/Kyndal

You'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 to
be 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. :)
 

Offline free_electron

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #37 on: April 20, 2013, 01:45:03 pm »

You'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 to
be 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. :)

That's all easy stuff. It's getting the calibrated chicken that's the hard bit...
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Offline codeboy2k

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #38 on: April 20, 2013, 08:54:27 pm »
That's all easy stuff. It's getting the calibrated chicken that's the hard bit...

Negative 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 laser :) Once this loop stabilizes only hens laying eggs in spec will be alive in the hen house :)
 

Offline c4757p

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #39 on: April 20, 2013, 08:55:43 pm »
Negative Feedback.

Dammit! I was going to say that.  :P
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Offline codeboy2k

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #40 on: April 20, 2013, 09:03:58 pm »
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.
 

Offline hairykiwi

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #41 on: April 20, 2013, 09:14:57 pm »
You are looking in the wrong place then. They have been going recently for $400

www.ebay.co.uk/itm/SRS-STANFORD-RESEARCH-SYSTEM-PRS10-RUBIDIUM-FREQUENCY-STANDARD-/130891002337

Thanks for sharing Zad. And /Bingo - It looks like they're relisted again. :)
 

Offline codeboy2k

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #42 on: April 20, 2013, 09:51:05 pm »
Chip scale atomic clock developed at the NIST in the USA :o

Lots 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

 

Offline hairykiwi

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #43 on: April 20, 2013, 10:20:50 pm »
codeboy2k - the specs on that device are really 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 to affordable frequency 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=ntp

According to one guy on that thread - alank2, it's accuracy is pretty impressive:
Quote
I finally got around to testing my rubidium frequency reference against a NTP server using your excellent NFT utility.
I ran it for 24 hours and it came out 0.00 ppm for first/last and all samples! I thought it would be some off...

And here's Kaspers original post for convenience. (His pdf and exe links are still working.)
Quote
If you have traceable frequency standards and several counters to choose from, this is likely not for you.

I have kludged up some software to let someone, with no frequency standard, and no counter, verify an oscillator to better than 1 ppm using an Internet connection. Then I thougt maybe this would be generally useful, and spent another day polishing it.

It works like this: The user's hardware sends characters* to a Windows PC's serial port at regular intervals. Both native and USB works. This drives a virtual clock in the pc, and this clock is compared against an NTP server on the Internet. After some statistics and regression math, out comes the offset. It takes about 15 minutes for 1 ppm.

http://n1.taur.dk/nft/nft.pdf manual with screenshots
http://n1.taur.dk/nft/nft.exe win32 exe

In order for this to work, an NTP server with a healthy refclock is needed. I've put in mine as default; If you are far far away from Denmark, you may want to find another, though mine may work perfectly well for you**.

Also, this is prototype software, so if it spits out unbelievable data, then it's probably broken.

License: This software is under Beerware license. If you find it useful, and we meet, you may buy me a beer.

/Kasper

*or a pulse the PC will interpret as a character. The value does not matter.
**unlike for timekeeping use, for nft static latency does not matter.
 

Offline grumpydoc

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #44 on: April 20, 2013, 10:33:21 pm »
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 1x10-8 to 1x10-9, Rubidium units should be in the in the 10-9 to 10-11 range.
 

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #45 on: April 20, 2013, 10:55:15 pm »
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 1x10-8 to 1x10-9, Rubidium units should be in the in the 10-9 to 10-11 range.

I 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. > x10-9
Sure you can get some good oven based oscillators, but they just aren't really the same level.
 

Offline codeboy2k

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #46 on: April 20, 2013, 11:11:49 pm »
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 10-11 or 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).

 

Offline olsenn

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #47 on: April 21, 2013, 12:09:40 am »
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?
 

Offline c4757p

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #48 on: April 21, 2013, 12:14:29 am »
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?

I'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.

Quote
How about circuits that compensate for the temperature-frequency variation curve?

You mean a TCXO?
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Offline olsenn

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #49 on: April 21, 2013, 12:58:55 am »
Quote
I'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.

Possibly, 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.

Quote
You mean a TCXO?

I 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?
 

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #50 on: April 21, 2013, 01:12:21 am »
Possibly, 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.

It'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.

Quote
I 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?

A 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.
« Last Edit: April 21, 2013, 01:16:39 am by EEVblog »
 

Offline chickenHeadKnob

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #51 on: April 21, 2013, 01:42:10 am »
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?

Take 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
 

Offline max-bit

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #52 on: April 21, 2013, 08:09:28 am »
that's my frequency standard :)









 

Offline codeboy2k

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #53 on: April 21, 2013, 03:15:41 pm »
Quote
that's my frequency standard
Nicely done max-bit  :-+

Would 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

 

Offline max-bit

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #54 on: April 21, 2013, 04:33:57 pm »








 

Offline max-bit

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #55 on: April 21, 2013, 04:38:33 pm »
Display bought in VK4GHZ
Other parameters
Pattern Trimble Thunderbolt GPS (bought on eBay)
Distribution Amplifier based on BGA616 (siemens)
4 out every 16 dBm at 50 OM
 

Offline bingo600

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #56 on: April 21, 2013, 04:50:25 pm »
Quote
that's my frequency standard
Nicely done max-bit  :-+

Would 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

I 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
 

Offline max-bit

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #57 on: April 21, 2013, 05:19:54 pm »
The relay switches the power supply is delayed.
So this power supply Cisco :) :)
And it was at the start of the power they give some noise so used a delay
In addition, the system suppressor, the thyristors. As the voltage exceeds 10% thyristor turns on, and the fuse is burning
Simple and effective
 

Offline hairykiwi

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #58 on: April 22, 2013, 11:33:47 am »
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 1x10-8 to 1x10-9, Rubidium units should be in the in the 10-9 to 10-11 range.

I 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. > x10-9
Sure you can get some good oven based oscillators, but they just aren't really the same level.

Thanks for the thoughts guys. To be fair, Kasper does say the Network Tranfer Frequency (NTF) project is better than 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 be really interesting to see how much better than 1ppm the NTF is - if anyone with a rubidium standard could spare the time please :)

If anyone's willing, here's the NFT project file links again:
n1.taur.dk/nft/nft.pdf
n1.taur.dk/nft/nft.exe

And if you could elaborate on how many order's of magnitude better a frequency standard really must be 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 the Open source Time Machine Project #2 (OTM-02) - a watch module for hobbyists and makers using the latest 128 x 128 Memory LCD and EFM32 ARM 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.
 

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #59 on: April 22, 2013, 12:20:19 pm »
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 be really interesting to see how much better than 1ppm the NTF is - if anyone with a rubidium standard could spare the time please :)

A 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?
 

Offline hairykiwi

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #60 on: April 22, 2013, 01:22:08 pm »
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 be really interesting to see how much better than 1ppm the NTF is - if anyone with a rubidium standard could spare the time please :)

A 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?

Thanks 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 pulse
To be understood by a 115200N81 uart, the pulse must have a high (>+3V) time of 8-78?s
when arriving at the PC RXD pin. If you have a max232 or similar between what you are
measuring 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 11kHz
repetition rate. A square wave of 6.4-11 kHz meets this, so 32768/4=8192 Hz would be a
good choice.
If you generate the pulse using a uart in a microcontroller, send a 0xFC character. The
baud rate does not need to match as well as it does for data; A baud rate between 230400
and 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
 

Offline kcozens

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #61 on: April 29, 2013, 07:14:48 am »
A 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?

I'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.
 

Offline rf-loop

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #62 on: April 29, 2013, 08:50:03 am »
A 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?

I'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.

Time 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?
« Last Edit: April 29, 2013, 08:55:15 am by rf-loop »
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Offline daddario

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #63 on: May 01, 2013, 06:41:41 am »
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.
My competence in HF electronics over 30MHz rolls off 3dB/oct.
 

Offline Bored@Work

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #64 on: May 01, 2013, 07:21:12 am »
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?

It 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.
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Offline ve7xen

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #65 on: May 01, 2013, 07:21:37 am »
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? :P
73 de VE7XEN
 

Offline daddario

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #66 on: May 01, 2013, 08:13:19 am »
It 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.

But 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).
My competence in HF electronics over 30MHz rolls off 3dB/oct.
 

Offline SeanB

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #67 on: May 01, 2013, 09:57:49 am »
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.
 

Offline LaurenceW

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #68 on: May 01, 2013, 11:28:25 pm »
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.
If you don't measure, you don't get.
 

Offline grumpydoc

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #69 on: May 02, 2013, 06:12:05 am »
> 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 x10-9 so if someone's "tweaked" it, it at least shouldn't be more than that out.

The one I have is within 1-2x10-11 of my GPSDO,
 

Offline bingo600

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #70 on: May 02, 2013, 02:39:09 pm »
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
 

Offline kkp

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #71 on: May 02, 2013, 06:05:00 pm »
> If the device is at least locking reliably (which seems to be the case), can I have confidence it must be working?

I 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.

/Kasper

who is at the moment doing adev plotting on a free GPS from someone in this thread.
 

Offline LaurenceW

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #72 on: May 02, 2013, 08:02:37 pm »
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.
If you don't measure, you don't get.
 

Offline casinada

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Offline carloscuev

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #74 on: June 05, 2013, 05:42:53 am »
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 3 http://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.
« Last Edit: June 05, 2013, 05:49:16 am by carloscuev »
 

Offline bingo600

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #75 on: June 05, 2013, 12:39:12 pm »
who is at the moment doing adev plotting on a free GPS from someone in this thread.

Blush ...  ;)

 

Offline bingo600

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #76 on: June 05, 2013, 01:24:57 pm »

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.

Go for a GPSDO

His shipping to EU is usually to high for me
http://www.ebay.com/itm/CIC-GGER-Equivalent-to-Z3815A-GPS-FREQUENCY-TIME-RECEIVER-10-MHz-/271213238400

Untested  :-\
http://www.ebay.com/itm/HP-SYMMETRICOM-Z3805A-GPS-Disciplined-Oscillator-GPS-Frequency-Time-Receiver-/181113452077

Tested
http://www.ebay.com/itm/HP-SYMMETRICOM-Z3805A-GPS-Disciplined-Oscillator-GPS-Frequency-Time-Receiver-/290832846664

Pricey but cool for a lab many 10mhz out - (seems to be of in the internal date) , but it won't affect the 10Mhz
http://www.ebay.com/itm/Datum-9390-52054-GPS-Disciplined-10MHz-Atomic-Clock-Time-Receiver-IRIG-B-1PPS-/281073499525


Both i and another person from this thread  ;)   has a Trimble Thunderbolt GPSDO (the old metal one)

http://www.ebay.com/itm/Thunderbolt-PRECISION-GPS-10Mhz-1PPS-Standard-Easy-Kit-/180419218430
http://www.ebay.com/itm/Thunderbolt-PRECISION-GPS-10Mhz-1PPS-Standard-Easy-Kit-/280649244485

http://www.ebay.com/itm/ThunderBolt-GPS-Disciplined-Clock-10-MHz-and-1-pps-/271207827869


But 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 antennas
http://www.ebay.com/itm/GPS-Timing-Reference-Antenna-26db-Gain-N-connect-/270881742870
http://www.ebay.com/itm/PCTEL-MAXRAD-GPS-26dB-TIMING-REFERENCE-ANTENNA-KIT-GPS-TMG-26NMS-NEW-/121121457131

http://www.ebay.com/itm/Nokia-470290a-101-Timing-Reference-Antenna-20-db-N-type-GPS-Waterproof-antenna-/290853216689


I think this is the one Trimble uses for the Thunderbolt.
http://www.ebay.com/itm/trimble-gps-antenna-p-n-28367-70-/290508227053



The 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
 

Offline carloscuev

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #77 on: June 05, 2013, 01:59:37 pm »
But we got them before the prices skyrocketed (Back then it was $110 for a unit , and $200 for a kit)

WOW $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.
 

Online EV

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #78 on: June 05, 2013, 03:42:32 pm »
WOW $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.

FE5680A is good but it is not easy to trim to correct frequency.

http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5680a_faq

Now 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
 

Offline carloscuev

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #79 on: June 05, 2013, 04:21:27 pm »
Now you need also GPSDO and your counter to check this FE5680A.
I was afraid of that.

You can do GPSDO yourself or buy a kit:
I think I'm going to go with this alternative :)
There 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=0
Which 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 output
http://www.ebay.com/itm/190849374321

Also a chinese SIMCOM module, not sure if it has 1 PPS output
http://www.ebay.com/itm/180795135748

There are also some Globalsat models, they have 1 PPS output
http://www.ebay.com/itm/140976661175

Sorry for all this questioning, I'm a long time hobbyist, but just starting to learn all this precise timing arts.
 

Online EV

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #80 on: June 05, 2013, 04:49:49 pm »
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=item3cb85a9f16

and these:
http://www.ebay.com/itm/10MHZ-ISOTEMP-Reserch-OCXO-134-10-CRYSTAL-OSCILLATOR-/170489162873?pt=LH_DefaultDomain_0&hash=item27b1f22c79

and 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.
 

Online EV

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Offline bingo600

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #82 on: June 05, 2013, 07:02:12 pm »
@Carlos

You'd need the GPS receivers that EV points at if you build the Miller GPSDO
The 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


/Bingo

Ohh i just found this one - more reasonable price
http://www.ebay.com/itm/TRIMBLE-GPS-RECEIVER-10MHZ-CLOCK-THUNDERBOLT-/171048961859

The TBolt needs 5v and +/- 12v , you can use a Cisco 1700 powersupply .. like here
http://www.ebay.com/itm/Thunderbolt-10mhz-GPS-Power-Supply-30W-12V-12V-5V-/280703342103

Or 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 antenna
http://www.ebay.de/itm/OPEK-3V-5V-GPS-1102-Active-Antenna-for-Garmin-G5010U-5M-/140892128742


« Last Edit: June 05, 2013, 07:13:23 pm by bingo600 »
 

Online EV

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Re: EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #83 on: June 05, 2013, 07:53:11 pm »
And you could start out with a cheap 5v gps antenna
http://www.ebay.de/itm/OPEK-3V-5V-GPS-1102-Active-Antenna-for-Garmin-G5010U-5M-/140892128742

I 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=item415803fb94

Picture about the finished device is attached.
 

Offline zibadun

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EEVblog #456 - CSIRO Rubidium Frequency Standard
« Reply #84 on: June 05, 2013, 08:49:26 pm »
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 :)
 


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