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Need help for HVHF pulse generator using function generator

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GrantX

Sun Oct 19 2014, 08:39AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

It looks like we've got a nice clear pictures of your intended applications now, so the range of relevant circuits can be boiled down a bit.

If you decide not to use a spark gap as the source of radiated RF power, then you could build:

- A CW solid state Tesla coil using MOSFETs or IGBTs as the high frequency switch, as Sigurthr said. These transistors are quite cheap and easily capable of the frequencies you desire. You could design a secondary coil with a large smooth toroid to avoid sparking, and it will radiate the majority of the input power as a huge RF field. Designs are easy to find online, but there will be little bit of effort put into soldering and testing the control circuitry and transistor bridge. An SSTC will usually require 2 DC power supplies, one for the low voltage logic and a more powerful one for the main input power.

- A vacuum tube Tesla coil (the electron tube mentioned earlier by Teravolt). Vacuum valves are older technology, but you can find large tubes designed for radio transmitting that can switch thousands of watts at hundreds of MHz if you needed them to. Again, you can construct a coil to radiate instead of make sparks, or use the CW plasma from the toroid as your source of emissions. Constructing and tuning a Tesla coil using a vacuum tube oscillator can be a very fiddly and tedious process of trial and error, unless everything is roughly calculated and you test and measure as you build. Plus, you will need transformers for the plate and filament supply, these can be expensive.

- Moving away from traditional Tesla coils and back to spark gaps, the DC resonant charging network posted by Ash Small sounds like a nice idea. You already have the 15kV NST, and with resonant charging you could have 40kV DC blasting through your spark gap if you wanted. Instead of trying to force the gap to fire at 1MHz, you tune the capacitor and inductor so the energy rings back and forth at your desired frequency. That's what I was hinting at in previous posts ;). The HV charging inductor will be a pain in the butt to source or build since it will need to withstand very high potentials, but it is still achievable. For the capacitors, I would personally look for big RF ceramics on ebay, which are quite plentiful. You could build an MMC of plastic film capacitors, but you will only need a low capacitance and will need very low losses, so a small bank of a few RF ceramic "doorknob" capacitors in series would be ideal.

Proud Mary

Sun Oct 19 2014, 10:40AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

You might learn something of interest in this ancient paper:

Spark Gap Switches for Radar

TwirlyWhirly555

Sun Oct 19 2014, 04:12PM

Registered Member #4104 Joined: Fri Sept 23 2011, 06:54PM
Location: Uk .
Posts: 122

The SSTC rout is a good way to go if you are looking for small setups .

I made a small 35volt SSTC that runs at 515Khz , but 1Mhz wouldn't be a issue as a secondary I made that's 2" x 2.8" runs at 980Khz .

Topload wise the easiest way I found was simple foil top covered in tape , worked pretty well .

This is the one I made for RF fields to light up neons , cold cathode tubes and things ,

Its a table top size , 12V driver , 35V Half bridge , fixed frequency driver , Mosfets are 50V/60A and survive a lot

IMG_0684[1] by TwirlyWhirly555, on Flickr

rororo74

Mon Oct 20 2014, 04:58AM

Registered Member #1124 Joined: Fri Nov 16 2007, 01:42PM
Location:
Posts: 17

Thanks GrantX. I was actually looking to avoid using a TC to achieve my goal. I know that a TC is an easy way to get to the MHz but it is not what I am after. I see that we have a misunderstanding about what I call RE (radiant energy). I do not mean the energy field surrounding the TC and able to light CFL at a distant. No, I mean the energy entering your circuit from the aether. This happens at the collapse of an explosive discharge e.g. SG. I never thought this would be possible with just SS systems but by the looks of things this thread seems to provide proof that it is achievable

Still reading page 58 but it seems there has been ample replication and collection of this energy is possible.
Thanks TwirlyWhirly555, that TC looks good!
I think I may move away from SG for now and investigate the simpler approach in the above thread, which shows that RE appears even in very low frequencies. When I master the way it is generated and collected then I will move to the next level. I have confirmation now that the secret is actually high rise/fall of a pulse of high voltage spike (no current required).
Thanks Proud for looking up the rotating SG for me.
This is my function generator.

Can anyone suggest a good circuit where I can isolate this from the power section and output my pulses in HV? I think optos do not suport HF.

Ash Small

Mon Oct 20 2014, 06:48AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

At first glance, that site you linked to looks to be pretty much pseudoscience. (discussions regarding 'free energy', etc aren't taken seriously on this forum)

If you are now looking at low frequency, single spike stuff then you are getting into the realms of EMP.

Some here have already mentioned that you could use a vacuum tube to switch high voltages, but the 'static gaps' in the paper linked to by Proud Mary also switch high voltage/high current. Both of these could be driven from your signal generator, via a suitable driver circuit.

rororo74

Mon Oct 20 2014, 08:23AM

Registered Member #1124 Joined: Fri Nov 16 2007, 01:42PM
Location:
Posts: 17

Hi Ash,
What I am talking about is RE. They call it back EMF and they claim to be able to collect it.
I make no claims. I just want a way to get my generator to drive a few mosfets so I can choose any frequency I like.
If you know of a good tried and tested driver circuit let me know. I will keep looking!
Thanks

Ash Small

Mon Oct 20 2014, 02:43PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

rororo74 wrote ...

Hi Ash,
What I am talking about is RE. They call it back EMF and they claim to be able to collect it.
I make no claims. I just want a way to get my generator to drive a few mosfets so I can choose any frequency I like.
If you know of a good tried and tested driver circuit let me know. I will keep looking!
Thanks

Yes, I know RE works, the first radio transmissions by Hertz used it in 1879.

1413816229 3414 FT166522 Hertz Schematic0

I was playing about with a sig. gen. driven circuit a few years back, which had resistors and capacitors to protect the sig. gen., and drive a Darlington pair to drive a flyback transformer at various frequencies. I'll see if I can find a link, but I pretty much decided it would be better to use a 555 timer to drive a MOSFET, the frequency determined by a variable resistor and capacitor, if I remember correctly (the safest way to protect your sig. gen. is not to use it

)

EDIT: This is a circuit that 'might' do what you want, but you'd need to modify it I expect. The flyback could be used to trigger something at quite a high voltage:

This is something I was playing with a few years ago when I knew very little about this subject. I think part of the cause of my failure was too long wires connecting components, resulting in stray inductance.

The rest of the thread is here, for what it's worth:

I imagine it won't be too difficult to learn a bit from this thread, and design something using a MOSFET, if preferred, but using a TL494 or NE555 is the route most people seened to suggest.

I, like you, wanted to use my sig. gen.

I might even have another go at something along these lines myself.

Antonio

Mon Oct 20 2014, 07:07PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

"Radiant energy" is a term without much technical meaning. Using electromagnetic circuits all the effects that you can obtain are just -electromagnetic-, with nothing that was not already adequately explained (or mathematically modeled) 100 years ago or more observable. On a more practical subject, mixing instruments (signal generator, oscilloscope, multimeter) and high-voltage circuits is not a good idea. A wrong connection or a wire that slips and the damage may be extensive.

GrantX

Tue Oct 21 2014, 04:11AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

rororo74 wrote ...

I just want a way to get my generator to drive a few mosfets so I can choose any frequency I like.

If that's all you need completed currently, and you are certain you want to use your signal generator, then just put a simplified Class A amplifier between the generator's output and the gate of the MOSFET. You'd literally only need one suitably-sized NPN transistor, a couple of resistors/caps and maybe two 9V batteries in series for power (18V delivered to the MOSFET's gate). Build it onto a small chunk of perfboard and place it in a metal tin for shielding (like a small pocket mint tin). You could use an optocoupler capable of 1MHz for increased isolation (I've used some capable of several hundred kHz so I'm sure you could find faster versions), or you could wind a gate drive transformer, but these are just superfluous accessories.

As others have said, a 555 or TL494 IC or anything similar could be used as a variable signal generator for driving MOSFET's if you don't want to risk your expensive generator.

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