Sure. A 1/4 wave is a short, just like an inductor. So the same methods would work.
That would be ideal for your 50MHz gated oscillator. It would solve the tempco problem forever, and give lower jitter as well.
It would also be perfect for a home-brew HP5370, which is no longer made. The interpolator might be fun, but well within the capability of many people here. The other part would be a stable reference oscillator, but GPS-disciplined oscillators are inexpensive. A well-equipped lab needs one anyway:)
Mold grows hyphae (a kind of root) into the things it feeds on. It loves cotton and other organic materials. Here is a SEM photo of a plant growing on a cotton fibre:
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This image is from the article below, where you see mold also growing on plastic:
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Clothing carries Aspergillus spores into hospitals. So when you visit your aging grandmother and give her a hug, she may die a week later from the infection you brought her:
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Mold grows on just about anything, including the concrete in your basement. Because it is so small it is usually invisible to the naked eye, so you can have a severe infestation and not be able to find it.
Here are some excellent images of hyphae and the mold life cycle:
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The links on this one are very good:
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Some more info on hyphae:
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You can kill the exposed part of the plant with bleach, but it grows back just like a dandelion when you cut the top off. So the only way to kill the root in fabric is to heat the wet material in a microwave until it steams. But you have to be careful and not let it dry under power, or it will catch fire. That is very dangerous since the inside is hot. As soon as you open it to look inside, oxygen reaches the material and it bursts into flame. The first instinct is to toss it in the air, which only makes the problem worse.
While growing, the mold excretes waste products to the outside. It also excretes the toxins it uses to combat other nearby molds, plus any other chemicals it cannot use, such as cyanide, from the material it grows on. This is called Exocytosis:
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The resulting combination can be so toxic that only microgram amounts are needed to be lethal in 24 hours. This is an ideal poison since the amount needed is so small, and it is metabolized in the body so it simply disappears and leaves no trace.
The spores have this coating, so when you breath them into your lungs, it can make you very ill. Humans developed long after molds appeared, so we learned to live with the spores and their toxins.
But exposure to high concentrations can destroy your ability to handle the spores, and you become very, very sick. That is what happened to me.
The spores have a coating of chitin, which is the same material in lobster claws and the bodies of insects. This protects the spore against most environmental hazards such as UV light and most chemicals. They are not affected by heat - even steam in a microwave won't kill them. It takes about 240F to kill most of them.
Sodium hypochlorite bleach, NaOCl, cannot penetrate the chitin and kill the spore.
However, ozone attacks the carbon bonds in the chitin, turning it into carbon dioxide. This destroys the outer coat and exposes the core, which kills the spore.
This requires fairly high ozone concentrations, about the maximum that can be obtained without using oxygen as a feed gas. It also destroys cotton, rubber, and most other organic fabrics, so you need to find clothing and bedding made of ozone-resistant materials. I'm hoping polyester clothing will survive, at least for a while.
Have you considered fast diodes? Just don't run them anti-parallel if you don't want to ruin your IP3. I often use +/-0.6V rails made via a couple more (cheap) diodes.
Please tell! We get ours from Murata, reels, special order, 10 week delivery. I'd like to get some different TCs to try, which is difficult under those circumstances.
You might consider a trick that usually works. Get one or two values of every TC that is made, all the way from P100 to N7500. I generally find that for my normal spectrum, 10 and 50 pf work just fine.
Then by a judicious mix of NPO (or the current COG) and a parallel or series standard TC I can have pretty much any coefficient I want.
Seriously, I'd try to avoid that. Controlled TC caps have become boutique parts, prone to vanish from the market in a jiffy and without a trace. Often all it takes is the termination of a major defense contract.
I saw that some time ago, but following the links didn't gave anything useful, besides strange. I didn't called them because I had no application ATM. I you find anything please let us know.
I've used them before. As transmission lines, they have very low impedances, ballpark 10 ohms, so to make an instantly-triggerable oscillator you wind up needing a lot of supply current. And they're expensive in moderate quantities and tricky to solder down. The lowest they go is about 600 MHz, and that's physically huge, so you're talking ECL drivers and prescalers. The whole product uses only 2.5 watts.
An LC oscillator is ideal for what I'm doing. If I could get some 18 pF N1000 caps, the osc TC would be about zero. As is, I spent most of the day taking temperature data and came up with a polynomial temperature curve I can use to tweak the varicap bias... all the hardware is already there... temperature sensor, tweak dac, varicap stuff. So I guess we'll go with a software fix.
The other thing that would help would be a zero TC inductor!
I don't dispute the cost, but that is probably insignificant compared to the selling price and to the time you spend fixing a problem that you don't know if it will recur.
Physically huge is a problem. Perhaps the helical versions would help solve that.
Tricky to solder is a process problem. You have experts that can figure that out.
I'm not sure about the lower frequency limit. Seems I saw some that went to
300MHz, but I'll have to check. Another divider stage would solve that, and give lower jitter at 50MHz.
I don't think low impedance is an issue. The 50MHz Colpitts you use now has an inductive reactance of 50 ohms.
The ceramic resonator acts as a high-Q inductor, so it should behave exactly the same, except at a higher frequency. The high Q gives less phase noise (jitter), and the frequency stability means you don't need to add much varicap control, which helps maintain the low noise.
The divider might be a problem. ECL would definitely burn your power budget. Is there any reason it has to be so low, such as portable battery- powered operation?
There should be a way around that problem. I have a simple battery-powered frequency counter from Radio Shack that goes up to 2GHz. I haven't checked the power drain, but it goes a long time on a set of alkalines. Regards,
Come to think of it, the higher Q with a ceramic means the oscillator would run at lower power, which would help offset the cost of the divider. It would also make it easier to start, so the start logic would need less power.
The LTspice circuit I posted could use a simple CMOS logic gate as the VCC source. I uderstand they now have risetimes around 500ps, which would provide a very precise starting point for the oscillation. This would be needed to take advantage of the low noise that comes with the higher Q.
The low impedance makes it need a lot of idle current. The best way to instant-start an lc (or coaxial resonator) oscillator at full amplitude is to run quiescent current into the L while it's off, and drop the current (quickly! like in 1/4 cycle, preferably less) to kick off the oscillation. That's the "initial condition". The only other initial condition that works would be zero inductor current and full capacitor voltage, but that implies a switch between the L and the C, which makes gobs of problems on its own.
If Il = 0 and Vc = 0 when off, it will take a long time to build up oscillation amplitude. I need it to start instantly.
Anyway, it works now with the computed temperature compensation.
John, check the LTspice circuit I posted. A great deal depends on the loaded Q of the tank. That raises the impedance at resonance. And that determines the quiescent current you have to use.
The circuit I posted improves the loaded Q by using a current source in the emitter instead of a resistor.
It passes (2.5-0.6) / 3.3e3 = 0.000575A through the inductor when off. That hardly qualifies as gobs of current.
It starts instantly. The first transition is positive, about 3.6V. The amplitude after settling is 3.9V. So it reaches 3.6/3.9 = 92% of full amplitude on the first half cycle.
There is a small "bump" in amplitude just after starting, but the zero crossings are not affected. The phase error during settling is smaller than I can measure in LTspice. That is measured in the second ASC file I posted, using two identical oscillators, with one starting after the other to compare the phase difference.
Since the coaxial resonator has 10X or higher Q, the tank impedance at resonance should be higher than obtainable with the 1206 smd inductor.
This means the power in the circuit is much lower, which means the tank current is lower. So it shouldn't need as much current when it is off, and it should outperform the 1206 smd version in every aspect.
The circuit I posted was just proof-of-concept. I didn't do any optimization before posting, especially in choice of transistors. I just grabbed whatever was available in LTspice.
So the performance could be much better than described here.
But if you are happy with the current 50MHz oscillator the way it is, that's all that counts. Regards,
You can make zero TC inductors. Air core inductor TCs come from dimensional changes due to thermal expansion, but the axial and radial expansions fight each other. From the usual simple formula for single-layer coils,
A**2 N**2 A=mean radius in inches, L(uH) = ----------- B=length in inches 9A+10B
you can compute dL/dT in terms of the CTEs of A and B. If you choose the ratio A/B correctly, and wind the coil on a mechanically weak plastic mount (so that A has the CTE of copper and B has the CTE of plastic), you ought to be able to make whatever TC you want, at least in the +- 100 ppm range.
The danger being that the plastic will cold-flow from the winding tension, and the frequency will creep over time. Lots of Coilcraft parts do that. Baking helps.
Is there a problem with the ASC file? Would you like me to archive and upload it to abse?
I could put a brief description with schematic and waveforms on my web site, but that might take some time. I have a very heavy schedule this weekend.
Also, I goofed in calculating the amplitude of the first positive peak. I forgot to subtract the 2.5V reference voltage, so the 92% figure is wrong. That is very easy to fix by changing the quiescent current. You can easily set the amplitude of the first peak to pretty much whatever you want.
I posted the actual concept here a long time ago. The base-collector junction of the transistor is forward biased when the oscillator is off. The current from a resistor betwen the collector and ground flows through the b-c junction and through the tank inductor.
Raising the collector voltage to VCC turns the transistor on and dumps the stored charge in the base-collector junction into the tank. The inductor back EMF forces the tank voltage to go positive at the same time the stored charge from the junction is forcing the tank positive. These two increase the energy of the first transition and reduce the quiescent current needed when the oscillator is turned off.
To turn the oscillator off, the VCC is removed and the base-collector juntion becomes forward-biased, applying the resistance across the tank. The transistor is turned off, so there is no power added and the tank energy dissipates through the collector resistance.
If you hit it at just the right point in the cycle, the energy dissipates very quickly, perhaps in 1/2 cycle. But other stopping points may add energy to the tank causing it to ring for 1/2 dozen cycles or so.
If you still would like to see the operation, please let me know how best to proceed.
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