Vintage Crystal Oscillator Teardown & Experiments
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- Опубліковано 25 сер 2024
- Taking apart an old NDK 48MHz ovenized crystal oscillator from the 80s, making some measurements; and taking macro shots of the quartz.
I make some initial frequency measurements before taking it apart, and then after ripping out the crystal I run it through a tracking generator to look for resonance peaks.
Interestingly the crystal seems to operate at a slightly different frequency to what's written on the OCXO packaging, and the 'big' crystal package actually has a small one buried inside!
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The small Crystal inside the larger case in my opinion adds another thermal filter. That would slow down any ambient temperature changes, as well as any overshoots of the oven control. As to the frequency, you found the series resonance. Disconnecting the rest of the oscillator circuit left the parallel resonance higher than the intended trim frequency and looks like you pointed to it, but did not tell the two frequencies separately.
That's how some pricey MEMS oscillators tune themselves in relation to temperature, making it extremely accurate.
The OCXOs I've collected all have SC-cut crystals that are operate at their fifth overtone (for extremely high Q). The set points of the ovens are all about 90 C. My favorite one is as stable as a rubidium source yet doesn't require periodic tube replacement. It has been operating continuously for more than ten years (thanks to diode-switched lithium-ion backup). I determined its precise frequency by using it to clock a Parallax Propeller microcontroller which itself was used to measure the 1pps output of a GPS receiver across many hours with 50 nanosecond accuracy. With that info, I could compensate the oscillator digitally. As a wall clock in my bedroom, it hasn't gained or lost a second in ten years. It has proven to be much more satisfying than the GPS or WWVB-based clocks it replaced.
Excellent justice you have paid to this small rock of Gibraltar!
Nice tear down. In the late 60's I used to order then expensive Hi-Q crystals to use in PYE Mark 3A, old low band VHF am radios. So as a teenager, my thrill was to rip out all the coils, divide the turns roughly by 2 and have them working on 27.240 AM and what ever other channels we could load into a channel change switch on the Pye that was not built with multiple channels.
Thanks for the teardown. I did a similar teardown of the OCXO in my HP 5350B many years ago and the construction was quite similar. Instead of using a TO-3 transistor for heating the oven, it uses a TO-220 one.
Kerry Wong
TO-66
The best part is the real crystal itself @ 9:35 . Thanks for a clear and nice video.
What is it with Aussies and taking things apart? Why can’t they just turn them on?
Seriously, thanks for sharing.
@xeke ‘ LOL. You never watched the EEVBlog, I guess.
Taik it appaaaat
The parallel resonance is the one that's easier to pull and a bit higher as well, it may be that they aimed at that?
The infinite crystal reactance is not really considered when designing. The crystal can be thought of as a low value resistor that works at a specific frequency. The crystal is used in an amplifier type circuit to provide positive feedback to the input. So the lower the resistance, the better the oscillation. Now, that being said, the parallel resonance has nothing to do with the Fp that crystal manufacturers specify. The Fp is the frequency that the crystal will be resonant with a SERIES capacitor to the crystal. Yeah it's stupid and it appears the sales people at these crystal manufacturers don't understand it anymore. But look at the specification. It will show an Fp @ XXpF. Let's say Fp is 10MHz @ 12pF. This means that the crystal will oscillate at 10.000000MHz with a 12pF capacitor essentially loading the crystal. Crystals such as the one in the video here should have a frequency and a temperature listed to show what frequency it will operate when brought to temperature. AT cut crystals start high in frequency and drop in frequency as the temperature increases, but when they go over the specified temperature, the frequency goes back higher again. There is a dip. This way the temperature can vary slightly with the least affect on the crystal frequency. Putting a capacitor in parallel with the crystal does nothing to the operating frequency Fs. It only changes the parallel resonant frequency.
I hope this helps.
Or small cracks in that oscillating Chrystal.
There could be multiple reason. It's still so close..
Did you terminate that output with some 50kohm resistor for testin? It could over oscillate, out of circuit where's it used..?
Those old units are so much larger and more complex than newer stuff. I have some Trimble OCXO's that are no bigger than a thick cookie.Bought on eBay for a few dollars. Need over an amp at start up but then settle down to around 0.2 if I recall.
The crystal case determines the so called holder capacitance C0, in addition, one needs to determine the motional inductance Lm, resistance Rm and capacitance Cm in order to fully characterize a crystal using the simple (Rm+Lm+Cm) // C0 model.
The whole unit probably did operate at the printed frequency and it malfunctioned thus why it was removed from the aircraft. Another indication is the warp pot not functioning, maybe it went bad or some capacitor went bad in the circuitry, who knows. I have seen things like this happen on old GE Mastr-2 and Motorola Micor and MSF2000 repeaters where a frequency would drift out of what was on the label because a part in the "channel module" went bad but the crystal itself was good.
Oven oscillators take a long time to settle. If the crystal was an AT-cut crystal, which is most likely but not for certain, then the frequency will drop when the power is applied. A normal oscillator with an AT cut crystal will start higher than desired and drop to very near the desired frequency. Your oscillator may have had a damaged tuning section with a shorted out tuning element. This would have made your frequency low to start with and it would fall from there with the oven heating the crystal. At any rate, it would have never settled on frequency if it were an AT cut crystal at this rate. The crystal was probably a 3rd overtone crystal and it should have shown a lot of frequency change when tuned. I have never seen anyone put a crystal case inside a larger crystal case. That is NDK, I guess. They are weird.
I'm thinking the oven never properly warmed up
When was the timebase of your counter last calbrated?Also these oscillators take several hours to come up to frequency and are typically left on continuously.They also need readjustment after having been 'off' for some time!
NDB = Non Directional Beacon. Used by aircraft equipped with a radio direction finder to locate the beacon and reference it to it's known location. With two beacons, pilots can tell where they are in relation to the two beacons and their angle to the aircraft.
They usually try to be closed to 5-10 MHz because it is more stable. They don't use the third mode but the fundamental and multiply it.
Too bad I can't find the oscillator just like this on eBay, its case is so nice I wanna repurpose for digitally controlled MEMS OCXO like SiT5721 (very pricey but kinda tempted to buy it for 10 MHz test source with Raspberry Pi Pico microcontroller on the new board in the rebuilt OCXO to keep it accurate).
It's possible it got dropped or subjected to mechanical shock. That can cause permanent changes to the frequency of a crystal.
I didn't notice any damage to the crystal but I agree that shock could be a possible culprit.
Perhaps that, but remember that quartz crystals are subject to ageing effects and given the age of the crystal, I'd expect to see some perturbation from the original frequency. Also, most of the circuitry inside the box is for temperature compensation; not so much for the crystal itself, but for the other components used in the circuit for the oscillator. I imagine that capacitors were carefully selected with opposing temperature coefficients so as to minimize the overall drift due to minor fluctuations in temperature. This older technology (which is still used today for some things) just goes to show how much technology has advanced in just a few decades! :) Thanks for the video, I much enjoyed it.
Thanks for great videos! Just a little correction - not babushka, but matruoshka :)
09:30
Some assembly error..
48Mhz is too high for a fundamental mode crystal normally. It's a 16Mhz crystal being operated at its 3rd overtone. You can see the resonant peak at 16Mhz on the trace before you zoomed in. I reckon someone printed the wrong freq on the rating plate as all your measurements indicate a freq of 48.027Mhz. Pity you had to butcher it s I suspect it was working perfectly.
I have seen some tiny 150MHz fundamental quartz crystals. The blanks are very small and there is no way you could make a wafer that large in diameter.
Thanks for the teardown. That insulation definitely looks like asbestos...
don't breathe this!
That's probably not asbestos. It looks more like some kind of fibreglass insulation. They didn't use asbestos in the 80s as by that time they knew about the health risks. Asbestos was used in the 1940s in radios as a heat shield.
Asbestos is harmless until you breathe it in or ingest it. Like mercury, it too is harmless until it becomes a vapor and you breathe it or you ingest it.
@@elfnetdesigns702 Basically anything poison is harmless until you ingest it in some manner. Therefore "everything is safe", LOL.
did you know, Dempa on its name if translated from japanese become (Signal or Frequency)
Nice to see but if you could speak a little bit slower it could be more interesting... Thanks.
I'd be careful about breathing in that insulation...
Your small cables = inductance!
The oven was probably busted and it could not heat it up to the right temperature to bring it down? maybe?
Hi, can somebody tell me the supply voltage to Nihon Dempa TCXO SC00001 4HMz. Thank you very much.
I aint to learned so I'd guess the difference between the frequencies on the box and the actual part is this was used in WWII as a decoding secret against the enemy (LOL), maybe though, and the reason why it was double wrapped is to protect the freq. of the crystal from being affected by gama rays or something else that I don't understand. NICE VIDEO though! ;-) very interesting
awesome video! very informative and interesting. Sadly I was really hoping someone would've shed some light on the whole little crystal in a big crystal package as it seems pretty strange to do, especially since it wouldn't really protect the crystal any better in any forseeable event and certainly wouldn't be cost effective
Someone mentioned above that it will slow down the temperature change. Personally, i think that's a bad idea but it was probably their way of thinking.
The Matryoshka structure of smaller oscillator inside a larger metallic enclosure was most likely done in order to suppress any electromagnetic induction from external sources (Electromagnetic radiation, EMI - probably a military aircraft) outside to the inner core of the crystal. Any EMI fields that penetrate to the inner can would cause eddy currents at the two electrode contacts, and a resultant fluctuation in the crystal resonance due to a fluctuation in the induced voltage. Hope that helps...
Your connection to the scope is throwing all the readings off. Better hope that insulation does not have asbestos in it.
9:05 it's not babushka, it's matryoshka "situation" :D :D :D
babushka is a gentle word for old woman, and i've never seen any old woman with another woman inside - this "situation" mostly happens to young women )
so mankind doesn't figure out the real uses of crystals
Exactly right my friend. Alien Technology. :)
Technology porn for us geeks , nerds and boffins ! 🧐🇬🇧🤔🤝👍🏻❤️🧠
Interested in watching more of your videos after you finish puberty.
Interested in reading more of your comments after you finish puberty.
How to destroy a nice vintage crystal oscillator.
6:58 That's not "strange". All Crystal Oscillators are labelled with the frequency they're manufactured for.
Could be double packed for shielding???