Effects of High Voltage on Quartz Crystal Resonance

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Күн бұрын

Пікірлер: 51

@LawpickingLocksmith Жыл бұрын

Back in 1980 I worked for a 2 way company as a field technician. Our UHF radios used crystals and to get the 25 kHz FM deviation they used the 9th overtone. Seasonal changes meant retuning then crystals, RX was on the 3rd overtone and easy to adjust but for TX I had to bring along a complete radio service jig to keep them radios within specs.

@Dennis-mq6or Ай бұрын

Sometimes your experiments are unique and interesting as heck. This was definitely one of those times. Thanks for sharing!

@SeanBZA Жыл бұрын

You could also drop the resonant frequency using a 2B pendil to add graphite to the surface of the crystal, which would lower resonant frequency slightly. Useful if you polished it a tiny bit high, getting it back down enough to work.

@joeteejoetee Жыл бұрын

I think that a truly "Lead" pencil would do the same. #NonROHS-Solder

@TheOpticalFreak Жыл бұрын

I would love to still get my hands on a vintage complete crystal set! 😃

@SeanBZA Жыл бұрын

I would think half of that drift is from the ceramic capacitors changing capacitance with applied voltage, you probably would need more stable capacitors to try it, as they likely are changing by a few pF, and changing the resonance of the crystal. Might be worth trying with a more voltage stable capacitor there. Incidentally with those crystals they likely are not synthetic, but were mined and cut from pure quartz deposits, likely from South America, which was for a long time the supplier of pure quartz.

@joesmith-je3tq Жыл бұрын

I will leave that up to you but a few things for you to consider. These are a class II part (X5V) rated to 5kV. We start to see a change at around 500V and I ran it up to about 1.4kV. No doubt that the voltage will effect their capacitance but we are always increasing the voltage across them which will decrease the capacitance. Yet, when we reverse the voltage, we see the resonance also change direction. A simple test you could try is to place an air capacitor in series with a crystal and measure the resonance. Now trim the capacitor to cause a 10Hz increase in the resonance. is it a few pF? At least with my part, we are talking about roughly a 50% decrease. Of course we also need a 50% increase to cause a 10Hz decrease in resonance.

@marcsmithsonian9773 Жыл бұрын

You see kids ! Thats a smart dinosaur, you mock dinosaurs, being born with your iphones in hand, but it takes a zenner diode in reverse and get back to zero bars.... not so smart huh ? Hehehehe.

@spvillano Жыл бұрын

Real dinosaurs know how to take an old backward wave tube and really make those kids cry. Alas, also angering to wrathful intent a certain rich Uncle Sam...

@marcsmithsonian9773 Жыл бұрын

@@spvillano rectyfier ? Wanna see trought their shallow mind :) no need for xray.

@spvillano Жыл бұрын

@@marcsmithsonian9773 rectifier, but not what a backward wave tube is. An old slang term for it was carcinotron, as it was cancer for microwave bands. Voltage tunable oscillator. It'd turn an old radar display into a display of rays, with no discernible returns. It'd also raise merry hell with modern cell phones, as they're microwave frequencies. While there are more modern voltage tunable oscillators, a proper dinosaur model that I could still work would be such a device. Used to repair to component level circuits that were tube based, hybrid, transistor (germanium and silicon), IC and VLSI, departing the field when IC's were ever so much fun to solder in, due to their resemblance to postage stamps, where the leads were the perforation edges. These days, I'd need jeweler's lenses or a microscope to work on the damnable things. Other than that, electrons are electrons, the laws of physics haven't changed and electronics is a field of physics. And yeah, for some readers, I do know how to use a tunneling diode as well. ;)

@ethanhodges4283 5 ай бұрын

@@spvillano Hats off to one of the ancient wizards of the world. I barely know enough to put together that a microwave frequency jammer really would make ipad kids cry. Lol Luckily I was born in the year of the Game Boy and got to see the changing of the Age, but I was wondering if you'd mind sharing some stories with me about the before times to now? My dad learned computer programming when a computer was a room of punch card machines, so I find it fascinating to learn stories about electronics then and the path experienced close up by people like you and him to get to today's pocket super computers. I'd be very grateful to hear some of your stories.

@joeteejoetee Жыл бұрын

FunFact: These "Vintage" Crystals' pins perfectly connect into an 8-pin Octal vacuum tube socket, and in some cases 2 at a time!

@RexxSchneider Жыл бұрын

Only a small point, but the resistors you used are marked as 3.9K, not the 3.6K in your schematic. Not that it makes any difference.

@joesmith-je3tq Жыл бұрын

True and in the first few seconds, I talk about 3.nnn kHz where obviously is it MHz. Then I repeat the same mistake. I'm sure there are others.

@vincei4252 Жыл бұрын

RIP. I'm surprised that frequency shift was so small. I'd have guess it would be over several kilohertz but now I know better!

@joesmith-je3tq Жыл бұрын

RIP? I really had no idea but was just curious.

@azinfidel6461 Жыл бұрын

About 10 years ago I was given a handful of chinesium fob remote controls. Inside was a battery a couple resistors capacitors and transistors. But what caught my eye was a round metal device that had four leads. It turned out to be what was called a SAW (surface acoustic wave ) device. Supposedly inside the device is a trapezoidal shaped Crystal with two leads at the small end and two leads at the large end. A signal was input at the large end causing the crystal to resonate. At the small end those vibrations would cause it to resonate at a higher frequency outputting a voltage. Essentially a frequency multiplier.

@digitalradiohacker Жыл бұрын

I don't see any problem with your test, other than the caps maybe leaking DC? The VNA should have been completely unaware of the DC you applied. Interesting test!

@joesmith-je3tq Жыл бұрын

Are you asking why the VNA was almost damaged?

@digitalradiohacker Жыл бұрын

@@joesmith-je3tq Not really - although I'd be interested to hear if anyone had some thoughts on it. My veiw is that the DC should have been competely invisable to the VNA because of the caps - so the only way it would have seen any of that is if the caps were "leaking" - Am I (as I often do) missing something?

@MarshalHorn Жыл бұрын

Yes, I think there's leakage through the high-voltage capacitors. Maybe the analog front-end saturated against one of the power rails and the nonlinearity broke the resonance calculations.

@ghlscitel6714 Жыл бұрын

Would be interesting to monitor the Q value of the crystal at higher burden voltages too.

@johnwest7993 Жыл бұрын

OK, now you're just having too much fun!

@PsychogenicTechnologies Жыл бұрын

I'm still trying to figure out how reversing the voltage changed the direction in the shift... it's not just tension. Is it the result of a physical imbalance in the crystal (meaning would flipping the xtal in the container reverse/flip the polarity effect)?

@LawpickingLocksmith Жыл бұрын

I love technical progress. But once we listen to digital transmissions and suddenly are held at ransom of having to pay for even the most basic news then I go back to analog!

@campbellmorrison8540 Жыл бұрын

Im surprised a flexing under high voltage didnt affect the resonance. If you applied AC to it I wonder if that would mix somehow with the resonance?

@MarshalHorn Жыл бұрын

Do you mean, affect the Q factor? I wouldn't expect the Q to be affected unless it's physically hitting one of the plates

@campbellmorrison8540 Жыл бұрын

@@MarshalHorn No I was thinking more of frequency mixing. Is there some sort of sum and difference generated in the crystal

@jim9930 Жыл бұрын

Ridiculously tiny dissipation factor of quartz...

@h7qvi Жыл бұрын

If a crystal has Q=10000 and ESR=50ohms at 7MHz, then reactance of the series LC is 50xQ = 500k. If the operating voltage is 1V (20mA through 50ohms), then the series LC components develop 500k x 20mA = 10kV, and this is in a normal operating circuit.

@joesmith-je3tq Жыл бұрын

I applied a DC bias in an attempt to cause a mechanical change to the crystal. When sweeping, the crystal will see both the AC and DC components.

@h7qvi Жыл бұрын

@@joesmith-je3tq The applied dc stress is small relative to the bending ac stress in normal operation.

@joesmith-je3tq Жыл бұрын

@@h7qvi And? I guess I am missing the point you are trying to make.

@joesmith-je3tq Жыл бұрын

Maybe a response to my comment about cracking the part?

@h7qvi Жыл бұрын

@@joesmith-je3tq The point is that the bending stresses in normal operation at resonance is hard to match by applying an external dc voltage. Therefore the system is still linear, superposition still applies, so frequency shift should be minimal. The constant stress from applied dc isn't affecting the elasticity of the material, so you'd expect little frequency change.