Rubidium Standard

[bsalai]

I bought a rubidium standard a while ago, but just got around to hooking it up. I'm wondering if what I'm seeing is normal.
Initially, it drew about an amp and a half but relatively quickly dropped to about .7 amp, all at 24 V. It is quite warm. You can touch it, but wouldn't want to leave your fingers on it.
It seems to be pretty stable after about half an hour. It reads 9.99999927 on my HP 5335A counter that has an oven controlled oscillator but has not been calibrated in who knows how long. I've been watching it for a while, about 45 minutes minutes, and the last digit was initially changing from 7 to 9 and back pretty slowly but seems to have stabilized at 8. If I'm counting digits right, that's tenths of a cycle. The current is coming down slowly. It started out (after the initial warm up at 1.6A) at about .7 A and is now down to .53 and seems to have stabilized there.
I'm seeing about .8 V out into 50 ohms, and just over 2 V into a one meg load.
If anyone else has one of these running, I'd be interested in whether this is consistent with what you see.
Finally, I'd like to build an amplifier/buffer to drive four outputs at about a volt for the other instruments here that can accept an external reference. Does anyone have any pointers to an appropriate circuit?
Thanks,
Brad



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[Gyro]

There has been lots of activity on the forum on the subject in the past, not in the last month or so that I remember, but a forum search for Rubidium will pull up lots of threads, teardowns, repairs etc.

It is normal for them to pull more current at startup (temperature stabilisers) and to run hot - I think most like to be heatsinked for a decent operating life!


P.S. Several people have modified Video distribution amps (modified for 50R) for distribution purposes.

[NivagSwerdna]

I used a LT6551 for a 4-way distribution... works pretty well.

https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg947866/#msg947866

And yes... very large start-up current until it's all warm and toasty.

[edpalmer42]

We could give you more specific info and/or links if you told us the make and model of your unit.

Ed

[bsalai]

The only number I can read is XHTF1003H.
I'll try to take a picture of the label.


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[bsalai]

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[edpalmer42]

I haven't seen any discussions on that model.  There might be something on some Chinese language boards.  It appears to be a Chinese clone of the LPRO, but it apparently has some form of RS-232 communications which the LPRO didn't have.  You're kind of on your own here, although info on the LPRO might be at least partially applicable.  Maybe edit the Subject of this thread to include the model number and see if you can find some others who have that model.  This could become the main source of info on this model.

Ed

[bsalai]

I tried to edit the title but it said I'm not allowed to move my posts??

I wonder if anyone can translate the descriptions of pins 3, 6, and 7? I'm pretty sure the other three 2, 4, and 9 are grounds.


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[NivagSwerdna]

Same as ?

[bsalai]

Yea


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[bsalai]

 Yes


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[edpalmer42]

I tried to edit the title but it said I'm not allowed to move my posts??

I wonder if anyone can translate the descriptions of pins 3, 6, and 7? I'm pretty sure the other three 2, 4, and 9 are grounds.


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I'm sure I've seen people edit the subject, but I've never tried it.

Are you sure about pin 9?  To be compatible with the LPRO, pin 8 should be ground, but not 9.

Regarding translation, it's possible to do it online, but you need a better picture than the one you posted.  First you have to do OCR to convert the picture into text.  Then you translate the text with Bing or Google.  Then you try and figure out what the heck the English means. 

Ed

[bsalai]

You're right, 2, 4, and 8 are ground. 5 and 9 are RS232.


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[bsalai]

Except for figuring out what the RS232 port does, and building a 4 port driver, it seems to be working fine. It would be nice to understand it more completely though.


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[Ash]

Hi,

I have one of these Rubidium oscillators as well. I'm planning on setting it up in a box with a small distribution amp etc.. From memory the original seller (it was a while ago) stated it was compatible with the LPro-101 (http://www.ham-radio.com/sbms/LPRO-101.pdf). Interestingly its not a direct copy inside..

I've used mine a few times to calibrate stuff I've repaired (spectrum analyser etc).

I translated the label on mine using the Google translate app on my phone..

Model: XHTF1003H
Number: 1 314205
Date: 201312
Chengdu Tianao Electronics Co., Ltd.

1 - 10MHz RF output
2 - 2 RF ground
3 - light instructions (lamp voltage??)
4 - chassis ground
5 - RS232 RXD
6 - 6 lock indication
7 - external frequency ESC (external frequency adjustment??)
8 - power ground
9 - RS232 TXD
10 -  + 24V power supply

The LPRO manual gives the following pinout.

1 RF OUT 470 pF PI - FILTER
2 CHASSIS GND SHORTING PIN
3 RF RTN (CHASSIS GND) 470 pF PI - FILTER
4 CHASSIS GND SHORTING PIN
5 LAMP VOLTS 1000 pF PI - FILTER
6 BITE* OUTPUT 1000 pF PI - FILTER
7 EXT. C-FIELD VOLTAGE ADJ. 1000 pF PI - FILTER
8 +24V RTN 1000 pF PI - FILTER
9 CRYSTAL VOLTS MONITOR 1000 pF PI - FILTER
10 POWER +24V 1000 pF PI - FILTER
* Built-In Test Equipment (unlock indicator)

So its probably not identical.. But close enough to get it working.

Cheers,
Ash.

[Dr. Frank]

..

. It is quite warm. You can touch it, but wouldn't want to leave your fingers on it.

Thanks,
Brad

Brad,

don't forget to assemble the unit on a big heat sink, like a metal sheet.
The interior ovens get hot to 76°C and 106°C, so the electronics MUST be cooled, otherwise will die soon.
It's necessary to limit the baseplates temperature to max. 65°C.

Frank

[bsalai]

Frank,

Thanks, I'll do that.

Brad


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[bsalai]

I've mounted a large heat sink to the base of the standard, and I"m letting it warm up to see how hot it gets. so far, about 10 minutes, it is warm, but no longer uncomfortable to touch. I don't have an easy way to measure the temp, maybe I"ll try my meat fork. I did, and after about half an hour it reads 43 C

Meanwhile, I've been monitoring the frequency with an HP 5335A counter, and the counter and the standard either drift at the same rate, or both are relatively stable. The reading is the same as it was the last time I powered the standard up a week ago, 9.999 999 28, and doesn't seem to be moving at all.

My question is, since the OCXO in the counter seems to have good short term stability, and perhaps long term as well, would it make sense to adjust it to 10.000 000 00?
If so, I looked at the documentation I have and didn't see a procedure for doing this, has anyone done it? If so, how?

I do recognize that this is a very small change, and adjusting it may be a bit silly.

Thanks all for the info and encouragement.

Brad

[Vtile]

I've mounted a large heat sink to the base of the standard, and I"m letting it warm up to see how hot it gets. so far, about 10 minutes, it is warm, but no longer uncomfortable to touch. I don't have an easy way to measure the temp, maybe I"ll try my meat fork. I did, and after about half an hour it reads 43 C

You need to get a few LM35 or LM234-x chips or something passive (thermocouple or PT100(0) ). 

[Dr. Frank]

I've mounted a large heat sink to the base of the standard, and I"m letting it warm up to see how hot it gets. so far, about 10 minutes, it is warm, but no longer uncomfortable to touch. I don't have an easy way to measure the temp, maybe I"ll try my meat fork. I did, and after about half an hour it reads 43 C

Meanwhile, I've been monitoring the frequency with an HP 5335A counter, and the counter and the standard either drift at the same rate, or both are relatively stable. The reading is the same as it was the last time I powered the standard up a week ago, 9.999 999 28, and doesn't seem to be moving at all.

My question is, since the OCXO in the counter seems to have good short term stability, and perhaps long term as well, would it make sense to adjust it to 10.000 000 00?
If so, I looked at the documentation I have and didn't see a procedure for doing this, has anyone done it? If so, how?

I do recognize that this is a very small change, and adjusting it may be a bit silly.

Thanks all for the info and encouragement.

Brad

Well done, the cooling, and also the measurement of the temperature!
The adjustment of the OCXOs frequency might make sense, as the Rb clock might be closer to 10MHz, as it drifts less.

Myself, having several HP OCXOs (i.e. 10811A-60111 in the 5335A and the 5370B), these have typical stability of around 10^-9, over many months, after all these years.
You can trim these OCXO to a bit better than that level, i.e. a few parts in 10^-10, provided, you always leave the 5335A plugged in, so that the single red LED is illuminated.

Your 7.2*10^-8 deviation is about 2 orders of magnitude bigger than what these OCXOs are capable of, so it makes sense to trim. (The "but" comes later.)

It's easy to adjust the OCXO to the same frequency as the Rb standard.
Simply apply the 10MHz from the Rb to the A - input of the 5335A, choose longest possible Gate Time, about 4 sec, and measure the frequency.
Open the lid of the counter, and adjust the OCXOs frequency, so that the counter reads exactly 10.000 000 00 MHz.

The 5335A resolves about 1..2ns / sec Gate Time, so it has at least 10^-9 resolution @ 4 sec Gate Time.

I made a modification on my counter to have 12.5 sec Gate Time on the front potentiometer, so my 5335A displays 10 digits.

Anyhow, if you have GPIB capability, you may also use Time Lab, a freeware program by ke5fx: http://www.ke5fx.com/timelab/readme.htm
It allows you, by means of the 5335A itself,  to measure the Allan Deviation of your OCXO vs. the Rb, and also to make precise adjustment of the OCXO in the frequency deviation measurement mode.

Here comes the "but": The basic problem, whether your Rb standard is still precise enough, you can solve only by taking the next step, that is acquiring a GPSDO receiver, and adjusting the Rb standard to < 10^-11.
May the Lady Heather be with you!

Frank

[NivagSwerdna]

I've mounted a large heat sink to the base of the standard, and I"m letting it warm up to see how hot it gets. so far, about 10 minutes, it is warm, but no longer uncomfortable to touch. I don't have an easy way to measure the temp, maybe I"ll try my meat fork. I did, and after about half an hour it reads 43 C

Quick question.... Why?  Isn't the oven meant to run hot so adding extra heat dissipation just makes it work harder? I can see that adding thermal mass might help stability but a heat sink?

[CJay]

No, they have optimum working temperatures like all components, they need a heatsink to keep them within that range and the oven is rated for that.

Running them without cooling can drastically shorten their lifespan, if you trawl back through the discussions of this on the timenuts mailing list it can be down to a few months instead of several years.

[NivagSwerdna]

Running them without cooling can drastically shorten their lifespan, if you trawl back through the discussions of this on the timenuts mailing list it can be down to a few months instead of several years.

I am highly skeptical.... but.... a bit of googling on my FE-5680A would suggest a dissipation of around 11W... hence mounting on a panel.

[Gyro]

Why the skepticism?

The unit contains standard PCB mounted components, including electrolytics. It also contains oven, Rb chamber, lamp etc. that run at higher fixed temperatures. If you don't heatsink the outer enclosure properly then the latter will cook the former.

All ovens need a certain amount of heat drain anyway in order to maintain regulation.

[CJay]

Running them without cooling can drastically shorten their lifespan, if you trawl back through the discussions of this on the timenuts mailing list it can be down to a few months instead of several years.

I am highly skeptical.... but.... a bit of googling on my FE-5680A would suggest a dissipation of around 11W... hence mounting on a panel.

I was of the same opinion as you initially, didn't seem to make sense, but the two FE devices I have are/were on heatsinks from the integrator so I'm inclined to believe the hive mind.

The FE-5660 I have is in a Tait T801 Frequency reference and is on a whopper of a cast alloy heatsink, the Fe-5680, when you see pics of the mounted, are always on some sort of thermal solution even if it's not a proper heatsink. I'm fairly certain I've seen advice from FE saying they should be as well, maybe in the FE-5680 technical reference?