Wide-range large gain amplifier question

Discussion in 'General Electronics Chat' started by Mike M., Oct 14, 2007.

  1. Mike M.

    Thread Starter Active Member

    Oct 9, 2007
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    If you have a waveform generator that operates over an 7-decade frequency range and a 500 KV low-current (microamps) DC generator, how can that be put together so that the AC waveform voltage can be increased to 500 KV peak-to peak over about 7 decades of frequency range?

    Is such a thing possible with a low budget of a couple thousand dollars if the DC and waveform generators are already owned?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Ahhh, you're going to use this thing inside a box that's completely shielded, sealed tight and grounded, right? Because otherwise, seems as if you'll be radiating lots of RF energy.

    Can't think of an easy way to do that offhand. Since your generator is +500 KV, you'd need a doubling circuit or transformer to get the 1MV PP.

    Seems like you'd need some really large tubes to control that much voltage. Running the grid would be another can o' worms. And of course, a large tube would limit your frequency range.

    Caps would be another problem. Mylar is 7kv/mil, so you'd need about 72 mil between plates. That's a long distance between plates for a cap.
     
  3. Mike M.

    Thread Starter Active Member

    Oct 9, 2007
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    Radiating lots of RF energy is what I want...........out in the barren desert of course (I live in Arizona). I would like to conduct some specific waveform tests on both water and rapid ball lightning production that can be "pulse pushed away" just after formation and directed at targets of various materials. There has also been a challenge out for a few years that will award 1 Million dollars to the person who comes up with a better way than currently exists to break large rocks into smaller rocks. I think targeting of rapid generation of ball lightning might just do the trick. If not, I'm certain that I will still get my money's worth back for what it costs for the equipment just in the entertainment value of generating ball lightning and finding out what it responds to and how it affects different materials.

    When you say tubes, are you talking about custom built vacuum tubes, like modified fluorescent light bulbs? 72 mil seems just a little too thin for 500,000 Volts. I was thinking more in the range of 3-4 feet for a capacitor that has a very low density dielectric material.

    I also have a large monolithic block of Aerogel that I would like to use as a dielectric for a capacitor but that would probably be 30-40 KV though.

    I was actually wondering if anyone manufactures single MOSFETs in that voltage and frequency range or if I could use a bunch of MOSFETs in series with a parallel signal to all the gates simultaneously.

    Speaking of high voltages, here is a tip for anyone that gets the flu and owns a neon lamp power supply...........
    Attach ONLY ONE electrode to a large piece of foil around your wrist at night when you go to bed and keep the other anchored down to a metal plate far away from you. You will be 80-90% to recovery by the morning and you won't feel a thing as long as the piece of foil is large enough. It doesn't even effect dreams like when large magnets are placed by your head while sleeping.
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
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    Heck no. Try e-Bay for surplus Russian stuff. I'm not kidding.
     
  5. Mike M.

    Thread Starter Active Member

    Oct 9, 2007
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    So would tubes or MOSFETs work better? Which one is the most expensive for similar ratings? What do you think?
     
  6. SgtWookie

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    Jul 17, 2007
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    MOSFETs are highly sensitive to static discharge, and once you "zap" them, they're done. :eek: Tubes would more likely than not survive a few travesties.

    Just because you're in the Arizona desert doesn't mean that generating broadband RF noise will be OK. You have Davis-Montham AFB outside of Tucson, and MCAS Yuma in the south - and MCAS Yuma has a HUGE ACMR (Air Combat Maneauvering Range).

    If your transmissions should happen to interfere with activities at either installation, or with general avation/fire/police communications, I will guarantee you that the authorities will hunt you down like a rabid dog. :eek:

    You better plan on building an RFI-shielded room if you want to be able to turn the thing on and stay out of the hoosegow. I'm not kidding.
     
  7. Mike M.

    Thread Starter Active Member

    Oct 9, 2007
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    Would grounded aluminum foil covering the the entire surface area (walls, floor, ceiling) of a large closet do the trick? Wait a second........ whistling plasma balls inside my house:eek:
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    It's going to be tough (and expensive) to build something that'll adequately shield RFI for that project.

    One of the BIG problems is how to ground such a room. If you're in high desert, the soil will likely be dry sand, and that doesn't conduct worth a darn. You'd have to sink several grounding rods deep enough to provide a solid ground - and I don't know how deep that would be offhand.

    Build your room out of copper foil, soldering all of the edges together. I'm afraid aluminum wouldn't work very well. The entrance is another problem - there is no really easy way to electrically seal a large rectangular hole. Using stuff like copper braid or grounding "finger" strips - even that has a resonant frequency.

    At couple of a former employers, both had built "shielded" rooms, lining them with about 20-gauge perforated copper. It was very expensive to build, and required constant monitoring - any leaks could cause big problems. (one of the rooms was for testing emergency transponders for aircraft - you can imagine the potential problems if that signal got out; and on occasion it did.)

    As I suggested, it's not going to be cheap.
     
  9. Mike M.

    Thread Starter Active Member

    Oct 9, 2007
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    Isn't it the CURRENT and FREQUENCY and NOT the VOLTAGE which determines what the effective RANGE of the signal is?

    If so, I wouldn't expect a few microamps to travel very far from the source and I wouldn't need shielding if that were the case. If it is current limited at 2-5 microamps, I can't really see that producing a long-range disturbance.

    Am I correct about this? Sorry, I have had very limited education on the transmission of AM/FM/Microwave.....etc.
     
  10. thingmaker3

    Retired Moderator

    May 16, 2005
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    Half a megavolt at five microamps is still in the walkie-talkie power range. Can you limit frequency to the 49MHz band? The FCC does not have a sense of humor, a soft spot, or a forgiving nature.
     
  11. Mike M.

    Thread Starter Active Member

    Oct 9, 2007
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    Actually I was going to shoot for the 24-26 Mhz range. Would they be cool with that range? I have a PWM that I can use to turn the current down to practically nothing..............Give it like a 1% duty cycle. I just need the voltage to be high.
     
  12. thingmaker3

    Retired Moderator

    May 16, 2005
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    Amateur Satellite. Standard Frequency & Time Signal. Land Mobile. Radio Astronomy. Broadcasting.

    At least in Arizona, you won't be interfering with Maritime Mobile...

    Build thee a Faraday cage!
     
  13. Mike M.

    Thread Starter Active Member

    Oct 9, 2007
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    Good God!!!! Is there anywhere in the frequency spectrum, other that audible, that isn't taken up by something nowadays??????
     
  14. thingmaker3

    Retired Moderator

    May 16, 2005
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  15. Mike M.

    Thread Starter Active Member

    Oct 9, 2007
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    It looks like all I have to play with for something like this is 0-6 KHz:mad::(
    Thanks for the handy chart!!! It strikes me a kind of odd that right around 25 MHz, the spectrum is allocated for "space research" when I have read many places that is a good frequency to produce laboratory ball lightning, or whistlers.
     
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