I work for FEI, a few notes. The 2 transistors soldered to the physics package are dual purpose, one forms the lamp oscillator. The other is used as a heater. Lamp temp is about 120C. Notice the small chip thermistor also soldered to the lamp housing. The cap you see stood up is intentional. It is a special high quality cap for high frequency. It is stood up and soldered directly to the coil around the lamp. The Q factor of the lamp oscillators resonant circuit is higher this way.
the blue cable actually in this design carries a relatively low frequency which is multiplied using a step recovery diode right at the resonant cavities lid. The bent over regulators are done for space and increased resistance to damage from vibe. This is a non vibe compensated unit but we do make them. Any other info you want ask me privately
Do you know how these units tend to fail? I'm wondering if lamp burnout is perhaps the most likely failure mode. I'm looking to purchase a unit that is not working, with hopes of repairing it. Lamp burnout would probably foil that plan! Sorry, I am unable to send you a PM.
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.
Amazing a man earning a living being an independent video blogger ....same as any reporter or presenter on the media but ...more interesting and only one person not a team ...not being rude about anyone but showing how to do something useful and interesting ...if more people get involved in electronics and create new inventions ...we all have the potential of becoming a genius if we get more involved in creating..well done Dave
Such an awesome little device! If I had a need for such a stable freq source, I'd be all over it. But receiving WWV is good enough for my needs (adjusting for sound card drift in ham radio applications). Thanks for all the info!
Hey Dave! I think I've figured out the reasoning behind that inexplicable foam and small disk shaped thing stuck to the crystal oscillator. I believe the foam is insulation, for a heater that regulates temperature in the oscillator.... but I just realized the two comments on my screen address the same thing I'm talking about lol
Regarding your question at 5:29, I think the disc on the crystal may be a PTC thermistor that acts like a temperature regulator to keep the crystal at a fairly constant temperature. This technique is often used in analog audio synthesizers to keep ICs such as transistor arrays at a constant temperature.
oh and the unit is thermally compensated for frequency over temperature. ie. put in a thermal chamber characterized from -20c to 70C and compensated... More important than the actual temperature is that it is STABLE temperature. Temprature fluctuations will cause a frequency shifts as the ovens adjust.
I actually like his voice and his video's. If you can't stand the pitch variations, use autotune or something. A lot of singers make it to the charts with it.
@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 :->
Great video! This particular FE-5680A appears to be one of the non-programmable ones maybe? Not sure. There are other models (with the same model name... FE-5680A) that have a SMA connector (on the same panel as the 9-pin D-connector, but is mounted on the opposite end of the panel) for outputting the sinusoidal signal - usually approximately 8 MHz, 10 MH, or 11 MHz, depending on the unit. The weird thing is the way they have the same model name for different units. Would be interesting to see why they do that.
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.
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 :-).
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Sorry if this was pointed out in a previous comment, but I believe the wee connector mentioned is a u.FL press-fit RF connector. Did you probe that connector to see what comes out? Maybe it's the output of the AD9832 after filtering?
I love your energy and enthusiasm it gets me excited about learning and trying to remember what I learned, I would love to go back to school but our education infrastructure is expensive because it's basically being defunded and privatized and I often wonder how education is in Australia, is it difficult or costly to go back to school, has it been privatized yet? I hope that's not getting too political or off topic.
+EEVblog How did the programming work out, i want to use one of these as a cheap master clock for studio purposes, thus id need the range from 44.1KHz to 192KHz out of the frequency standard, and if i recall correctly ill need to convert it to square wave as well.
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?
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.
*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.
I started looking for info about the Rb standards due to a construction article (//hackaday.com/2012/08/02/atomic-clapperboard/). Good stuff - You've answered all my big questions. The pellet attached to the crystal Y200 is probably a ceramic heater. These control their own temperature despite changes in applied voltage. When insulated by foam, you form a Crystal Oscillator Oven. Thanks!
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How do you program different frequencies for FE-5680A Rubidium Standard? Do you need separate electronics or is it all built in? I want to make a reference clock for Digital audio use (A Esoteric CD player with clock input). Needed is 44.1khz or 88.2 kHz etc. I would appreciate your advice. Thanks. Jake - England
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.
