EEVblog #236 - FE-5680A Rubidium Standard Teardown

[Mikkel324]

The foam is indeed for thermal insulation. Both the lamp and the resonance cell need to be quite hot to work (to keep the Rb in vapor form). Most of the input power is used to heat these parts, not to drive the lamp. This is why it takes a few minutes to start up and why it draws a higher current during startup.

The "tombstoned" cap is not a bodge. The Rb lamp is RF-excited and this cap is the resonant cap in series with the exciter coil. There's probably a high RF voltage on the free end.

[qwaqwa1960]

*Intentional* tombstoned cap!? Yeah, right.

Piezo? Uh huh... PTC as already mentioned.

The foam is almost certainly thermal insulation.

But, hey, thanx for making the availability of these magnificent beasties known!!! Mine's on its way. Plan to slap on a little touchscreen GUI and a high-freq DDS, and end up with a 1? ppb 0-400MHz generator. Nice.

[UnbrokenCheese]

I picked up one of these about 1-2 years ago, and started to build a nixie clock around it. Kinda lost interest in nixies. All I have to do is finish writing the AVR firmware (NOT Arduino), but it'll likely keep being a dust collector.

[CampKohler]

Can you find a schematic for it?

[zaprodk]

I think the stuff on top of the xtal is a small PTC pellet for heating it!

[aljaz55]

@zaprodk

I agree. It looks like a PTC, which is bacically a self-regulating heater.

[clodester]

I love your videos but your constant surprised inflection which gets higher and higher makes me for and unknown reason, very anxious and in a strange way, worn out just listening.

But excellent vids, just talk naturally.

[EEVblog]

@clodester I *AM* talking naturally. It's called a High Rising Terminal, google it. Common in Australia. Not everyone speaks like a Yank.

[clodester]

@EEVblog I know not everybody speak like and Yank. That would be worse. In ENGLAND, where I live, we also use the term high, or rising infliction.

[OcctU]

@EEVblog

"Not everyone speaks like a Yank"

I've listened to people from the USA, Canada, England, Singapore, etc, you name and none of them talks like you. Why don't you just admit that you have a rather odd voice? You seem to be ashamed of it.

[linagee]

Changing the frequency of this rubidium clock may not work as great as you hoped. I looked at the programmable one on ebay. It said it doesn't work so great and that there might be a bandpass filter in the circuit somewhere. So I'm not sure if this can totally replace a high quality (expensive) freq generator.

[Albinorama]

at 7:28 is the physics package makin interference with the videocamera?Sounds like a mobile phone.That thing is heavy radioactive!

[nodariel]

Its beautiful. lovely hardware porn.

[linagee]

Would a Clock Tamer have a higher frequency stability than the rubidium standard you tore down? It synchronizes to the GPS clock.

[ketturi]

Very interesting, teardowns are my favorite :)

Maybe i should buy one sometime. It would be very cool to build a atomic nixie-clock time standard with on of these, but because they heat up and are power hungry, i probably go with normal crystal and some RTC chip.

[First2ner]

what will you use it for?

[headsplosive]

I can hear your cellphone RF during entire video.

[gglovato]

Dave, shouldn't you update the copyright at the end to (c) 2012 ?

[EEVblog]

@gglovato Yes, but I'm too lazy.

[heroineworshipper]

Looks like it could have been made somewhere besides China. What other country is there?

[jdesbonnet]

I love that term 'physics package'. The last time I heard that term used was in the context of the interesting bit inside a nuclear bomb :)

[awesomelightning]

Dave, join 4HV and make the community have 4 daves. And go on the chat forum!

[Ryantron9000]

Three great vids in one day! Thanks Dave I'm learning tons!

[xXdenhartXx]

Awesome, keep it up!

[kkpdk]

The version you have there can be trimmed a ppm up and down over the serial interface. Not useful as a function generator, but quite enough to adjust it (step size is 10^-13-ish) during production.

The oscillator runs 60MHz, and a high harmonic of that, mixed with 5.5MHz from the DDS, produces the 6.8GHz required. For a frequency standard this is the better one, as it has less phase noise. Now you just need to cal it :-).

[jacgoudsmit]

Time to change the copyright message to 2012 :-)

[kevtris]

looks like that crystal has a PTC thermistor soldered on top of it to make a cheap crystal oven. the foam would help insulate it. a PTC will self-regulate the temperature, so long as the input voltage is constant.

[EEVblog]

@kevtris Makes some sense with the foam, but what's the other piece of foam trying to isolate I wonder?

[ashsama2]

@EEVblog Temperature stabilisation...

These days we make rubidium oscillators in MEMS at work, sure makes them smaller :)

[RichsRobots]

Awesome video Dave. Brought one of these and boxed it up it last year, great pieces of kit (and cheap on ebay!) , never felt the urge to take it apart though!

[Gameboygenius]

7:45 The thing you labelled a bodge capacitor is marked E3. There's also a wire going from something marked E15 on the board up to the lamp can. What's E supposed to mean? A choke?

Maybe the foam is meant to be heat isolation to help keep something's temperature stable?

[GiorgioCapocasa]

Very neat construction!

Loved it: thanks :)

[therealjammit]

The MAX3232 looks like it's hooked up to four unpopulated surface mount components. The serial might not work without those components.

RF jack J8 looks promising.

[Psychlist1972]

What a neat box. Thanks for the teardown, Dave

[rgvrr1]

Great video as usual, Dave. Hope you talk about the actual frequency accuracy you get out of your FE-5680A.

[PirateRadioPoland]

So I think it's time to build an atomic alarm clock!

[EEVblog]

@PirateRadioPoland Begging for it! Some of these have 1pps output too.

[lpg42t]

@EEVblog @PirateRadioPoland The 1pps is not synced to UTC.. whats the point of a "atomic" clock if its not dead on.

[envisionelec]

It's actually a crystal heater with a PTC, not a vibration sensor. ;)

[EEVblog]

@envisionelec Looks awfully like the piezo-ceramic vibration sensors I've worked with. But of course that wouldn't make much sense unless they are doing something really obscure. A heater does make more sense :->

[fingerboy18]

Wow, Dave. You're releasing videos like a madman and I love it!

[Psychlist1972]

Still processing! Someone must have gotten on YouTube's naughty list. Time to have Edgar send a few thousand volts down the wire.

[turbochargedbrick]

Please check back in a few minutes.

[Psychlist1972]

Still processing. As Dave might say: "wah wah" :)

[timmylc]

ughhhh "This video is currently being processed" ~sad face~ :P