Thinking about a 80MHz crystal - as a detector

Any possibility of inserting a transformer at the front?

steve

Or low impedance series resonance...

Prove it- what makes you think it is Johnson noise, because it is represented as a resistor symbol?

Acckk, how am I going to do that? I'm making an assumption. Maybe someone else can give us an answer, references, etc.

It's back to basics for you. The book by Nye on the physics of crystal should have the answer. Physical Properties of Crystals, Oxford, still going through late editions, will be in nearly any technical library.

Just speculating, not sure what you're actually detecting, but do some Google searches for "microcalorimeter" and see if this is what you're trying to do. To oversimplify they are looking for energy deposited into a crystal giving some tiny phonons of quantum vibration, and looking for this at extremely low noise levels.

I know the nuclear physics side (hint: these experiments are usually buried deep in mines or inside mountains), but always got lost in the solid-state phonon stuff.

Tim.

I don't understand this. Is the crystal itself going to be exposed to the e-field, or is there an antenna of some sort, connected to the crystal?

If the crystal is used directly, is its metallization the antenna?

Is there any advantage over using the crystal in the front-end, as opposed to matching+amplification followed by a narrowband, maybe crystal, filter? A well-matched fet amp can have a noise figure well below 1 dB.

And of course, the crystal series resistance behaves, from a Johnson noise perspective, just like any other resistor. Conservation of energy, again. Ignoring microphonics.

John

Wouldn't 80MHz fundamental crystals be mesa crystals? How does their Q compare to bulk crystals?

P.S. I think you'll get more grant money if you use MEMS resonators instead of boring old crystals. Nanotech would be even better.

The crystal's mechanical properties are actually somewhat anharmonic, which is why the overtones aren't in exact harmonic relationship. This could be used as a detection mechanism. Otherwise it sounds more or less like it's being used as a high-Q tank circuit for impedance transformation, which isn't altogether unreasonable.

Providing that there's a dissipative process going on, this is right, and that's what's going on in the crystal. The fluctuation-dissipation theorem again.

There was that guy ten years or so ago who made a big stir with a "lossless resistor" for switching circuits. I never really learned the details, but he got a big IEEE medal or something for it. Does anybody remember?

Cheers,

Phil Hobbs

AFAIK Johnson noise happens to any dissipative 'thing' that shows up as an electrical effect -- all that matters is the apparent resistance and the temperature. AoE actually mentions this.

Or an impedance matching network. One adjustable coil and a pair of caps will do almost anything you want them to, and you don't have to worry about the assembly being too narrowband compared to the crystal. If that doesn't float your boat then you can get 3:1 trifilar broadband transformers from Mini-Circuits that'll bring that optimal match up to

Check out "Radio Frequency Design" by Wes Hayward -- he goes into detail about noise matching in an RF environment (which you should already know) but also about using transformer feedback to get a power match at the same impedance as a noise match.

In article , Winfield Hill wrote: [....]

Is there gas around the crystal? There will be noise from the atoms smacking into it, if there is.

Crystals aren't very linear at very small or very large signals will this be a problem?

Someone at Berkeley was using a tiny ring core to detect the magnetic field that the electrostatic one implies. You may want to google on this to see if it worked.

wasnt it a transmission line followed by a dc-dc converter or somesuch?

I vaguely recall reading a paper at the time, but forget the details. ISTR his examples were all puny wee things,

:)

I wouldnt want a belt from one of your 10kV gadgets though (electroporesis perhaps?)

I just scanned thru the last 6 years of IEEE professional comics, and couldnt find a mention of it. but upon further recollection I think my explanation is roughly correct, and the examples he gave were about 50W or so. the lack of mention this century suggests it wasnt so great after all though.

I'm doing some design work at the moment for a 200KVA converter. Only problem is, there is nowhere to plug them in at home :( Even my neighbour (a joinery place) only has a 60A 400V outlet. So I'm going to make a 2kVA prototype first....

fault currents get quite exciting with the big stuff. IGBTs limit fault current to around 10x their rated current (depending, of course, on Vg) so my 300Arms converter has to cope with a peak fault current of about

I tried to estimate last night how much money has been spent training me over the last 15 years, its a LOT. Tens of millions of dollars. No wonder smart companies work hard to retain staff. I once destroyed $1,000,000 worth of fancy flywheels, one at a time :) (OK, its not that bad, I tried to operate them at their rated load etc, and they all failed in various ways)

on an analogous note:

Air NZ is looking at laying off a whole lot of engineering workers in NZ (they do all their own aircraft maintenance, and contract to others too). I wondered why, until a friend who is in the military set me straight. A few years back, we neutered our air force - we no longer have planes with guns; any offensive air capability will only come about through hiring saudi pilots ;) so the air force no longer trains all the associated personnel. So Air NZ cant hire pre-trained technical staff, but has to train them itself. which it cant afford....

Cheers Terry