Scoping Signals in the 10s of Kilovolts

[Marco]

wrt high voltage avalanche transistors, afaik, any BJT will avalanche

AFAIK the term avalanche is a bit overloaded ... they can avalanche to the open base breakdown voltage instead of fully turning on, the former is slow and will cause the transistor to burn a lot of power. There might be some very high voltage BJTs which avalanche to turn on, but I guess it will take experimentation to see which they are.

[alm]

so as long as you've got less than 40KVdc applied to the probe for less than 100ms and less than 10% duty cycle and you're below 8000 feet, you will do fine.

But what if it's a 100 ms pulse of a 40 kVrms 100 MHz signal (assuming it's filled with freon)? Based on Fig. 1-2, I would say that the frequency would be derated significantly. The manual does not appear to make any statement on how frequency and duty cycle interact, so it's not obvious to me whether the maximum voltage would reach the same 40 kV(rms) maximum at short pulse durations, or a much lower maximum. A very short pulse with ns-level rise times would even have even more high-frequency content, but a much shorter pulse duration and lower duty cycle.

[Eviltech]

What i want to ask is why do you need such crazy frequencies with that lazer and how exacly do you get >100Mhz signals trough a transformer. I'm asuming you are not using aircore.

[TerraHertz]

madshaman, do you have ieeexplore access? "DC to 1 gigahertz multikilovolt voltage probe" describes a self-built probe, self built by master student with access to a metal shop and a network analyzer though.

Bah. $31 for non-members.
Guess I'll just have to do without it, since I am currently broke. Bad case of Ebay splurge syndrome.

Thanks for the link!  What are you working on?

In general, an interest in the behavior of arc plasma paths as HF transmission lines.
Specifics - don't wish to say, due to potential commercial applications.

Not opposed to HV transformer oil of some sort.  The reason I immediately thought of paraffin is that:

a) it's an excellent insulator
b) it's a solid a lower temperatures and I can avoid accidentally spilling it all over my lab ^^' and I figure it's much less messy to work with
c) I can go buy it in large quantities pretty much anywhere and I've used it before

Hmm... actually, you may have converted me. For small setups anyway. I've only used it as sculptural material for lost wax process, in which you burn it out as fast and hot as possible. But I suppose slow heating would be much less 'sooty'. Would still be very hard/impossible to do with large systems though.

(it also makes a decent shield for high speed neutrons for when I'm older and crazier and start work on that Farnsworth reactor ;-))

Now there's a well worn garden path, with some amusing twists.
Here's a quote from Richard Hull, owner of http://www.fusor.net
"There is absolutely no posibility of ever making a fusion generating reactor here using any scientifc methodology and amateur funding." (sic)

Heh. Saved for future value.

Coupling it to a CCD sensor sounds like a good idea! Did you try any fast single shot captures yet?

No, not yet.  Ironically, I've got my mainframe working but repairing the 7A29 modules I have is still on my todo list.  I've gotten as fas as buying the Tek camera mount I'm going to retrofit but that's all; I don't anticipate too much trouble, the only thing requiring real work will be rigging up the circuit to trigger it at the right time.

Assuming the image capture time of the CCD can be faster than the decay time of the 7104 tube phosphor. Which I have no idea what that is.

A tinkerer after my own heart, guess what 20Ghz sampling scope I have too ;-).  I've been drooling over the 50Ghz test set, but I cant justify paying $2000 for one (which is the best price I've seen so far), I don't really need it and imagine my joy if the thing turned out to be fried.

Have you looked at HP 83480 lightwave modular scopes? I haven't tried buying a system yet, but it looks like with lucky deals you could get a very cool set for well under $2000.
For my use, the bonus would be getting optical sampling in the 10s of GHz too.
ebay search: (83480a,83481a,83485b,83486a,11898a,83487a) -cd

Oh yeah, and F*CK ebay for their latest insane revision of searching. Goodbye 'saved searches', welcome our new 'followed searches' overlords, in which there is no way at all of avoiding your 'followed searches' cluttering your ebay landing page with hundreds of unwanted 'Feed' photos. Good job ebay management, you pack of retards. Why don't you all go get a job at Facebook?

[Marco]

Guess I'll just have to do without it, since I am currently broke. Bad case of Ebay splurge syndrome.

Yar, matey do you really want it?

You're not missing much though, he basically skips the math behind every important design decision and the exact measurements aren't in there either. The only thing I really learned from the paper (other than that it's possible to make such a probe relatively cheaply) is the idea of putting an antenna wire parallel to the high resistance leg of the divider, connecting to the centre of the divider through a resistor with an unexplained value, inside the ground shield to compensate for the high order fall off caused by the distributed capacitance to ground across the resistor.

Whether he just experimented with the wire to get a reasonable transfer function or whether he used EM field simulation before fabricating ... no idea.

[ElectroIrradiator]

Oh yeah, and F*CK ebay for their latest insane revision of searching. Goodbye 'saved searches', welcome our new 'followed searches' overlords, in which there is no way at all of avoiding your 'followed searches' cluttering your ebay landing page with hundreds of unwanted 'Feed' photos. Good job ebay management, you pack of retards. Why don't you all go get a job at Facebook?

The writing was on the wall, once they removed wildcard searches. I'm not even sure what all of this is supposed to accomplish. Do they expect their customers will buy *anything* with a subject line looking remotely similar to what they are looking for?

Sorry for OT derail.

[TerraHertz]

Yar, matey do you really want it?

Aye, I do be wanting it. Even if it's as scurvey as you say, still interesting.

You're not missing much though, he basically skips the math behind every important design decision and the exact measurements aren't in there either. The only thing I really learned from the paper (other than that it's possible to make such a probe relatively cheaply) is the idea of putting an antenna wire parallel to the high resistance leg of the divider, connecting to the centre of the divider through a resistor with an unexplained value, inside the ground shield to compensate for the high order fall off caused by the distributed capacitance to ground across the resistor.

A wire parallel to the divider resistor, in a HV probe? Er, in an insulating medium?

Whether he just experimented with the wire to get a reasonable transfer function or whether he used EM field simulation before fabricating ... no idea.

I do. He didn't simulate. If he had he'd have been proud to show it.
The problem with gear like this, is the lack of calibration signals. Where do you find a nice clean 100KV square wave?

[Marco]

A wire parallel to the divider resistor, in a HV probe? Er, in an insulating medium?

Well air, it's only designed for 15 kV ... and you can of course use an insulated wire, just pot the end.

[madshaman]

What i want to ask is why do you need such crazy frequencies with that lazer and how exacly do you get >100Mhz signals trough a transformer. I'm asuming you are not using aircore.

I might be less confusing if I talked in terms of risetime as opposed to bandwidth.  The 1Ghz bandwidth is roughly what I need to see the pulse shape.

The only transformer that *might* be involved in my project would be used to trigger the avalanche in the marx-generator-like circuit.

This type of laser cannot operate in CW mode, increasing the pulse repetition rate is much much further down the line.

(you might confusing my posts with other general discussion in the thread around the same topics)

[madshaman]

@Terrahertz

You're not the first person to consider using plasma to carry signals or as an antenna ;-). 

Best of luck though, I'll be doing some experiments with plasma soon, but more for artistic expression.  I'll be happy to share notes.

wrt ieee: I had access to both ieee and and acm at my former employer (named after a fruit ;-p), but I was a lowly senior SE.

I pay for personal memberships in both out of pocket.  Honestly, having access to so many academic papers (given one's math is halfway decent) is invaluable.

In the loosely grouped hacker community I've participated in, there was an unspoken philosophy that holding back your techniques can lead to fear that you'll never ever come up with a better idea in the future.

Now that I've switched fields and become independent (very recently) I'm more of the mind to publish *after* I've released a product to the market.  If someone wants to use my ideas (which I assume aren't globally unique) they could always just RE my product anyway.

I'm still not entirely sure where I fall on this, because it *is* painful to spend countless hours with pen, paper and mathematica, prototyping and refining and then have someone just copy you; here I'm referring more to software I've written.

That being said, I generally assume there are at least one million people at least as smart and knowledgeable as myself and for who the exact same ideas will occur.  It's depressing, *but*, only a small number will actually put in the work to bring their idea to life.

If we didn't live in such a commercial global society it would be clear how inefficient non-sharing can be, but we don't live in an ideal world.

Also, I do believe that if someone puts in long hours, works very hard and makes the sacrifices that this requires, they *do* deserve a better lifestyle.  There are always those more than willing to leach off another's labours in one way or another.

I'm trying to find a balance myself with regards to this in my whole life, I'll let you know if I find a solution ;-)

[TerraHertz]

@Terrahertz

You're not the first person to consider using plasma to carry signals or as an antenna ;-). 

Sure, I know, nothing secret about that. It's a particular application idea that I'd like to experimentally check out before opening my mouth.  Partially to avoid looking like a fool if it's a stupid idea, partially for ... other reasons.

Best of luck though, I'll be doing some experiments with plasma soon, but more for artistic expression.  I'll be happy to share notes.

Cool. Strangely enough 'plasma art' is another thing I want to pursue. Since I'll have pretty much all the required gear set up for the other project.
I hear that 'plasma spheres' are illegal to sell now. Not sure of the details re what kinds, but I can understand the worry about X-Rays. It's something I'll have to be very careful of with my main project. Hence spending $1K on a gamma ray spectrometer. Vacuum, ions and HV are not a good mix, on your own side of a big lead shield.

wrt ieee: I had access to both ieee and and acm at my former employer (named after a fruit ;-p), but I was a lowly senior SE.

I pay for personal memberships in both out of pocket.  Honestly, having access to so many academic papers (given one's math is halfway decent) is invaluable.

Currently I'm very poor. Also I take the position that 'knowledge' isn't valid unless it's freely available to all. Academic paper paywalls make me very angry. Even when I could afford to pay, I refuse to.

In the loosely grouped hacker community I've participated in, there was an unspoken philosophy that holding back your techniques can lead to fear that you'll never ever come up with a better idea in the future.

Ha ha... lack of ideas is not a problem I've ever had. Quite the opposite.
And don't worry, if it works you'll hear the details.

Now that I've switched fields and become independent (very recently) I'm more of the mind to publish *after* I've released a product to the market.  If someone wants to use my ideas (which I assume aren't globally unique) they could always just RE my product anyway.

I'm still not entirely sure where I fall on this, because it *is* painful to spend countless hours with pen, paper and mathematica, prototyping and refining and then have someone just copy you; here I'm referring more to software I've written.

That being said, I generally assume there are at least one million people at least as smart and knowledgeable as myself and for who the exact same ideas will occur.  It's depressing, *but*, only a small number will actually put in the work to bring their idea to life.

If we didn't live in such a commercial global society it would be clear how inefficient non-sharing can be, but we don't live in an ideal world.

Also, I do believe that if someone puts in long hours, works very hard and makes the sacrifices that this requires, they *do* deserve a better lifestyle.  There are always those more than willing to leach off another's labours in one way or another.

I'm trying to find a balance myself with regards to this in my whole life, I'll let you know if I find a solution ;-)

We'd have an interesting conversation f2f, I'm certain.
Too bad we've only the net (hi there NSA), since there are many things I won't talk about online.
Which, considering the kinds of things I do sometimes talk about here (to the annoyance of the mods), should make you wonder about that.

[ElectronicTonic]

Glad to help. I just now remembered another helpful video for when you have some better BW. It's Mike Harrison showing how to probe a 100 MHz clock signal which is not easily done with a typical scope probe.

[madshaman]

@TerraHertz:

wrt: cash strapped: I hear ya, I've been very poor at certain points in my life, here's a couple hints as to how I'd get by:

1) shamelessly pirate software

When you have real money, you really should dole out the cash for a tool you like and use.

2) ask a good friend still in uni for their digital library credentials; in my day (after leaving uni) this usually took the form of a web proxy and login information for it; then you can (usually) freely access *all* the electronic journals through the university's library site (well, whatever set the school pays for).  Not sure if it still works this way for most schools.

Again, when you *can* afford, pay for the appropriate memberships and journal access.

wrt: f2f, well, Australia's on our list for places to visit eventually, I'll let you know if we're ever in the area!

wrt: secrecy, ABSOLUTELY no worries, I still wrestle with this.  I would love a world where there weren't any patents and everyone would freely share all their research, but imho, it isn't remotely practical at this point in history.  Best we can do is find a nice middle-ground.  Most bleeding edge technology starts as peer-reviewed academic research anyway.

wrt: plasma globes, I'm fairly certain that no off-the-shelf globe uses anywhere near the acceleration voltage needed to produce high energy photons, and even if they did, there's waaaay too much matter in the way for any particle to attain enough energy before colliding with another for it to be a risk.  Spontaneous decay in the world around us is probably a more dangerous source of x-rays (as in no danger at all).  I think you can still buy them in Canada, but I'm sure the paranoia will reach here eventually.

Cheers!

[madshaman]

Glad to help. I just now remembered another helpful video for when you have some better BW. It's Mike Harrison showing how to probe a 100 MHz clock signal which is not easily done with a typical scope probe.

Thanks again!  Man, I'm grinding my teeth over not being able to see Dave and w2aew's newest videos, not to mention the latest eps of walking dead :-(

[johansen]

wrt: secrecy, ABSOLUTELY no worries, I still wrestle with this.  I would love a world where there weren't any patents and everyone would freely share all their research, but imho, it isn't remotely practical at this point in history.  Best we can do is find a nice middle-ground.  Most bleeding edge technology starts as peer-reviewed academic research anyway.

psychopaths always rise to the top, its just how the world works.

I would say that about 50% of bleeding edge technology starts as academic research, the rest as accidental inventions..
however, most accidental inventions are rediscovered years later as academic research.