corrugated oscillator

If you make the grooves deeper, you've got an unwound magnetron. Maybe it'll work with shallow grooves, at reduced gain.

Use magnets instead and you've got a free electron laser.

Tim

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"John Larkin" schrieb im Newsbeitrag news: snipped-for-privacy@4ax.com...

go clean that tube, there is probably some object (paper/cardboard) stuck inside ban Apricale, Italy

I don't think so. The tube is pretty much transparent, and any such would be pretty obvious. I think there's a fundamantal resonance going on with the corrugations... the oscillation is very high pitched, nowhere near the "twirly" tube resonance.

It also occurred to me that a transmission line that used nonlinear capacitors might have a similar oscillation mode, but at least the DC bias mode can be dismissed on conservation-of-energy arguments.

John

If you put RF into such a line, you can get nearly all the power coming out the far end at a higher frequency. At other input settings, you get a large amount of noise on the far end.

You can do the same in a lumped constant case. Take a 1N400X diode and put it in series with a 1mH or so inductor. Wire it to a function generator and put a scope on the voltae on the diode. Tune for the resonance at a low amplitude. Now fiddle with the amplitude and frequency and perhaps the DC offset. At some point, you will get chaos coming out of the diode.

That's like a NLTL "shock line." They can turn a relatively slow input pulse into a 5 ps, 10 volt rising edge.

I have a paper somewhere on a pulse-sharpening NLTL that uses ceramic caps as the nonlinear elements, at the 2KV sort of level.

Using an AC pump does *not* violate conservation of energy, so all sorts of stuff becomes possible.

John

I wonder if they'll ever come out with a material with high permeability and permittivity which saturates in the same ratio. You could make a shock line with constant 50 ohms impedance. In some cases, you want the voltage increase (physics experiments), others you don't (sampling head?).

Tim

Saturating-inductor NLTLs are fairly commonly used to generate high-power fast pulses. Some big ic-exposure eximer lasers do this to speed up an IGBT switch.

Good point about L and C. If both elements change value together, you can keep Z = root(L/C) constant as the pulse compresses.

That's a little hard to visualize this time of morning.

John

A BWO is what I thought of too. I used one of these in the past, but I'm not real clear on how they work.

George H.

It won't be a transmissionline effect if it's high pitched as you write. That is the case with those tubes you swing around and they start making noise and jump from one harmonic to the other. But higher modes are damped because of losses on the surface on the points where the velocity is high. Your noise must be coming from turbulence on some sharp edges. ciao Ban Apricale, Italy

There's a child's toy that uses that effect. It's a rough corrugated hose you swing around by one end.

Cheers

Phil Hobbs

That may be a flute/coke bottle mode, with the air blowing across the tube inlet. What I heard was very high pitched and seemed to be caused by high-velocity air flowing over the corrugations.

John

Could be--though if so, it would have to be an organ pipe mode rather than a Helmholtz mode as in a bottle.

Fun toy, though.

Cheers

Phil Hobbs

A piece of paper will make such a noise when stuck in the vacuum hose.

You know the trick... hold taut piece of paper horizontally in front of lips (not unlike a reed on a clarinet, saxophone, oboe, bassoon :-) and blow. ...Jim Thompson

Yes, but there's also an interaction between the flutter of the air stream itself and the organ pipe mode. Vacuum cleaner hoses typically have 0.5-inch pitch spirals when fully stretched, which corresponds to a ~13-kHz fundamental flutter mode.

Was it as high as that, John?

Cheers

Phil Hobbs

That would be a magnetron, right?

TRAPATT oscillator diodes kinda use nonlinearities and time delay, but are only one-trapped-cycle devices. SAW filters are the other wave-past-multiple-obstacles electronic gizmo that springs to mind.

But the big application of corrugation and electron beams is the free-electron laser (you can get coherent X-rays with a suitable undulating magnetic field and a big electron beam).

I couldn't say from memory, except that it was quite high. Next trip up, I'll take a scope and a microphone. The sound did happen only when the hose was stretched.

John