Challenges of creating a powerful programmable signal generator - Page 1
Forum section: electronics / beginners

author: adras
author_rank: Regular Contributor
timestamp: November 09, 2023, 04:57:11 pm
content: How do I start this?Hmm, I have reason to believe that I really really need the following signal generator. Here are the specs:Fully programmable digital frequency(see below)Input Power 400 WattOutput Voltage > 1MVAdjustable Output PowerRegarding the frequency. Minimum spec is 5 MHz(ideally as low as possible), Maximum 15 MHz (ideally as high as possible). I also want 10 points per interval, so that when I have period of 1 second length, I want to be able to program the frequency with 8 Voltage points.Now to me all of this sounds almost impossible, however if anyone can achieve this, it's you guys.Where could we start designing this? I don't care if this thing needs a f.... Intel Processor.

author: jonpaul
author_rank: Super Contributor
timestamp: November 09, 2023, 05:45:15 pm
content: Tow devices needed !MOPA = Master oscillator + power amplifier.j

author: ejeffrey
author_rank: Super Contributor
timestamp: November 09, 2023, 06:17:42 pm
content: Quote from: adras on November 09, 2023, 04:57:11 pmA 1 megavolt output delivers more than 400 watts into a 1 gigaohm load -- not counting any internal losses of course. So your first step is to make an output stage that can handle this much voltage with no appreciable loading -- including radiative losses. So I don't think your power budget is going to be realistic.First off, you won't get anything like those specs with a semiconductor or vacuum tube output. You will probably need to generate a high power lower frequency oscillator and use a transformer. Essentially like a Tesla coil, except those are usually pulsed operation, < 1 MHz frequency, and resonantly tuned. Achieving specs like that with a broadband tunable system capable of CW operation is going to be... quite tricky.

author: radiolistener
author_rank: Super Contributor
timestamp: November 09, 2023, 06:23:54 pm
content: Quote from: adras on November 09, 2023, 04:57:11 pm1 MV = 10 GigaWatt power for a usual coax line with impedance 50 Ω. I didn't hear if such amplifier exists at all.More real value is 10 kV = 1 MegaWatt power, if it's enough for you, you're needs to build something like this:Note, that such 10 kV amplifier will require dedicated high voltage transmission line to deliver 2-3 MW power from local electricity supplier to your 1 MW signal generator facility buildings.If you're still needs 1 MV and planning to build 1 GW signal generator, then you're needs to build nuclear power plant consisting of many high-power nuclear reactors. Because it is required in order to supply your signal generator with enough electricity power...

author: adras
author_rank: Regular Contributor
timestamp: November 09, 2023, 08:23:25 pm
content: As far as I'm concerned 1,000,000 Volts @ 400 Watt = 0,0004 Amps. What's wrong about that?I also noticed there are some really powerful BJTs out there, 2.45ghz@300 Watt. So a high frequency, "high power"(400Watt) primary doesn't sound like a big issue. But I'm definitely not an expert

author: adras
author_rank: Regular Contributor
timestamp: November 09, 2023, 08:24:47 pm
content: I'm not interested in high power like MegaWatts, I'm only interested in high voltage @ very little capacity and current

author: radiolistener
author_rank: Super Contributor
timestamp: November 09, 2023, 08:36:57 pm
content: Quote from: adras on November 09, 2023, 08:23:25 pm1000000 V @ 400 W = 2500000000 Ω = 2.5 GΩAt 15 MHz looks impossible. Even 1 MΩ will be very problematic (if possible at all).And what kind of transmission line you're planning to use to transfer the power from generator to a load?There is no coax cable with 2.5 GΩ impedance.Usual coax has 50 Ω or 75 Ω, symmetrical feeding line or waveguide can have a little higher impedance, but not significant.So, if you want 1000000 V @ 15 MHz, then you're needs 1 GW power amplifier and about 2-3 GW power supply.You can ask NASA, if your project will be interesting for science or military, may be they agreed to spend some trillion dollars of taxpayers to build something like that

author: Manul
author_rank: Super Contributor
timestamp: November 09, 2023, 08:47:23 pm
content: Quote from: adras on November 09, 2023, 08:23:25 pmQuote from: adras on November 09, 2023, 08:24:47 pmThe point is, you want AC and kinda high frequency. For AC we think of impedances. For example, at 10MHz, 10pF capacitance will have impedance of around 1.6kOhm. That's the problem.

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 09, 2023, 08:50:38 pm
content: I wonder what the application could be. Is it something legal?

author: ejeffrey
author_rank: Super Contributor
timestamp: November 09, 2023, 11:03:09 pm
content: Quote from: adras on November 09, 2023, 08:24:47 pmAt high frequency that's just hard to achieve.With 1 MV, you need large electrodes spaced far apart to avoid arc discharge, corona effect, and capacitive coupling. But at MHz that is a recipe for an antenna.

author: ejeffrey
author_rank: Super Contributor
timestamp: November 10, 2023, 12:40:02 am
content: To have 1 gigaohm reactive loading at 10 MHz you need capacitance of 17 attofarads.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 10, 2023, 09:16:10 am
content: Quote from: adras on November 09, 2023, 08:24:47 pmits ok to dream big... thats the 1st step to achieve wonders.. if you can pass the 2nd step, ie doing the reading, ask guru and papa etc, then you are ready for 3rd and bigger step which is actually building it.. or 4th, ask people to build for you and get quoted the price.. by the time you passed those steps regardless of success or failure, then you'll realize how important it is to dream by little.. fwiw...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 10, 2023, 03:17:41 pm
content: I'd have to do some figures to get a more accurate number, but I suspect, for any dimensions of components, or electrodes thereof, that can stand off such voltages (i.e. ~1m), the radiation resistance alone would consume five orders of magnitude more power, let alone the resistive losses in the elements from driving their capacitance.Consider: 15MHz is 20m wavelength, 1/2 wave is 10m, so a 1m dipole structure (that is, two electrodes this distance apart; their shape is immaterial, a dipole isn't just a length of wire cut in half, any blobby shape will do), will have roughly (1/10)^2 times a regular one or say 1 ohm radiation resistance, or ballpark 10kohms parallel equivalent, and (1MV)^2 / (10k) = 100MW.I have no idea if air even breaks down the same way at such frequencies. The structure would be big enough that even spontaneous ionization (by field or by cosmic rays) and cyclotron motion probably have roles to play, making air itself much more conductive, or indeed breaking down into streamers.To be sure, breakdown in air will not be what you are expecting, if your platonic ideal is the average Tesla coil. At these frequencies, corona discharge is instantaneous, brush- or glow-like, and streamers are continuous (persistent over many cycles of excitation).At the very least, if nothing else, it will have to be under oil, and in a metal enclosure (to shield radiation, so the fields manifest as capacitance, not radiation loss). But you can't circulate oil fast enough to keep the resonator cool at that power level, of that size and frequency. It would have to be superconducting more likely, and thus in hard vacuum in a cryostat; polished niobium rod (coiled as a helical resonator), inside a chamber made of the same, would be the most likely option. Then you'll have a Q factor high enough to achieve such voltages at the requested power level (or only a few orders of magnitude more, considering the cryocooler's input as well).Needless to say, it'll be a massive exercise in futility as you can't interact with the field inside a superconducting cryostat in any meaningful way; even the slightest imperfection introduces extreme losses, and the voltage goes away.Tim

author: Marco
author_rank: Super Contributor
timestamp: November 10, 2023, 05:30:14 pm
content: Variable frequency is right out, but a fixed frequency solid state tesla coil under oil might get you close. The load would have to be at the top, for instance a small oil filled dielectric heating chamber. The load is part of the tuning of the system of course.PS. coat the box in lead, if the load starts sparking it's an xray generator.PPS. squared power hits harder than I expected, a small 100 kV SSTC is already burning a kW in copper losses. 1 MV gets ridiculous. Best wait for room temperature superconductors.

author: ebastler
author_rank: Super Contributor
timestamp: November 10, 2023, 05:36:40 pm
content: Quote from: adras on November 09, 2023, 04:57:11 pmSeeing this (and in the Beginners section!), I have reason to believe that you are mistaken.

author: radiolistener
author_rank: Super Contributor
timestamp: November 10, 2023, 06:28:11 pm
content: Quote from: Marco on November 10, 2023, 05:30:14 pmSince a high energy is involved, there is a sense to coat it in a thick uranium layer for better shielding

author: TimFox
author_rank: Super Contributor
timestamp: November 10, 2023, 07:20:11 pm
content: Lead is a lot cheaper than depleted uranium.https://www.energy.gov/sites/prod/files/2020/11/f80/2021%20CRM%20Price%20List%20Draft%20V1_Nov%202020.pdf

author: Marco
author_rank: Super Contributor
timestamp: November 10, 2023, 08:11:43 pm
content: I couldn't find a modern reference for a radio frequency MV range transformer, but I did findan ancient one.A small quote :QuoteThat's purely copper losses, which is in the same order of magnitude I estimated for driving a small solid state tesla coil to a MV.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 10, 2023, 08:57:48 pm
content: Quote from: TimFox on November 10, 2023, 07:20:11 pmeven if can get cheap, if the person is a kind afraid of cutting his own pcb due to risk of pcb fibre or asbestos particles inhalation, concerned about leaded solder tech, got solder smoke sucker fan at home, dont diy Li-Ion/LiPo battery because afraid of explosion hazard... live in california... etc etc, just forget it...https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2819790/

author: adras
author_rank: Regular Contributor
timestamp: November 11, 2023, 08:37:05 pm
content: Quote from: SiliconWizard on November 09, 2023, 08:50:38 pmOf course, I just want to do a wide range of experiments, I could also get 50 devices, these specs just cover all of them

author: adras
author_rank: Regular Contributor
timestamp: November 11, 2023, 08:39:49 pm
content: Quote from: ejeffrey on November 10, 2023, 12:40:02 amThat just sounds like some careful placed wiring. When I look at my rigol oscilloscope it clicks from time to time. I suppse those are relais turning certain parts of the circuit on and off. That scenario definitely needs it's own scenario. I hope speaking in pcb traces 17 attofarads should be achievable

author: MarkT
author_rank: Frequent Contributor
timestamp: November 11, 2023, 08:43:19 pm
content: Sounds like the spec's for particle accelerator acceleration electrode amp, except the power is way way too low. Has to be resonant, has to be in a vacuum, for those frequencies and voltages I reckon. 1MV is not a signal voltage!!I note the dV/dt (rate of change of voltage) for a 10MHz 1MV is 63 teravolts/second. Though a tiny stray capacitance of 0.1pF that's going to push 6.3 amps... That's definitely high energy physics!

author: adras
author_rank: Regular Contributor
timestamp: November 11, 2023, 08:45:05 pm
content: Quote from: T3sl4co1l on November 10, 2023, 03:17:41 pmThat's something I'm looking for, yes. Tesla coils are already getting into the domain I want to enter, however I want to have more adjustability

author: adras
author_rank: Regular Contributor
timestamp: November 11, 2023, 08:46:13 pm
content: Quote from: ebastler on November 10, 2023, 05:36:40 pmThat's why it's supposed to be adjustable, I can get myself a low level shock and then stop playing with it

author: adras
author_rank: Regular Contributor
timestamp: November 11, 2023, 08:49:12 pm
content: Quote from: Marco on November 10, 2023, 05:30:14 pmIf I look at what I can get for 5000 Watts, I should already get something nice @400Watts

author: Marco
author_rank: Super Contributor
timestamp: November 11, 2023, 09:24:37 pm
content: Quote from: adras on November 11, 2023, 08:49:12 pmYou'll get something which can ignite a flame, but that's not continuous AC. It's ringing up and down. It's funny the generator from the video was single coil though, the Sloan RF HV generator from the thirties was single coil too (he called it a resonance transformer). According to him a coupled coils Tesla coil had too low efficiency.At the end of the day, whether dual or single coil, the coil is a resonant tank and at a MV RF a resonant tank will have ridiculous copper losses.

author: adras
author_rank: Regular Contributor
timestamp: November 12, 2023, 03:09:21 am
content: Oh, btw, I posted this in the beginner section since I am the beginner. Just imagine me as a child with big dreams or a 40 year old, whatever.Anyway. Let's start off small. I recently bought a signal generator board: AD9833, SPI controlled with Sine, rectangle and an interesting range. Now theoretically it shouldn't be too hard for one of you guys to boost the output to a 300 watt range, right? What about only for a certain voltage/frequency range? Don't try to eat the cake all at once, let's go step by step for this. Because, in the end I'm not able to adjust it at an infinite speed so it is very well allowed to switch between modes.I'm just wondering how the final box is going to look like. If it fits into a shoe box or two or if I neet to rent some property to put it on. But actually, with a total input power it can't be too big. If given wire resistances I'm not able to achieve 1MV that's fine. But then I'm going to change my specs and I include the Minimum Range for another starting point (the old one still exists) at a frequency of let's say less that 20kz down to less than 1hz. At least that way there are sparks flying at 1MV think marx generator etc.

author: adras
author_rank: Regular Contributor
timestamp: November 12, 2023, 03:12:03 am
content: Oh, and regarding these signal generators, they also exist for RF frequencies. And as I saw in the schematic of the board there are also variable resistors, which are used to boost the signal. And I recently saw that there are transistors @300W at 2.45Ghz, which makes it possible to generate microwave ovens with integrated circiuts.Come on guys, my specs can't be that insane!Pretty please

author: MarkT
author_rank: Frequent Contributor
timestamp: November 12, 2023, 03:24:49 am
content: Kilovolt levels would be feasible, but megavolt? That's a million times the power requirement...

author: Marco
author_rank: Super Contributor
timestamp: November 12, 2023, 04:25:19 am
content: Quote from: adras on November 12, 2023, 03:12:03 amUnless you want to make some ludicrous class AB amplifier, MV requires a transformer. The transformer will have limited self inductance at RF and enormous amounts of current will be induced to go with the enormous voltage.Maybe at some low duty cycle something could be possible, a ms of RF per second?Here'san tesla coil based pulse generator which gets near a MV and seems to resonate at a couple MHz .... the transformer is possible, it's the power needed just to deal with copper losses which is the problem.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 12, 2023, 04:37:56 am
content: even kV 100Hz is not an easy.. googling can give some hint.. pulse gen is a different game.. let alone MHz range even at kV. not an expert i could be wrong..https://www.google.com/amp/s/www.electro-tech-online.com/threads/how-to-amplify-function-generators-output-to-several-kv.123347/%3famp=1

author: Marco
author_rank: Super Contributor
timestamp: November 12, 2023, 04:55:23 am
content: I'm not sure anyone has even done anything similar to what's requested since the 30s as a somewhat traditional transformer (at a single frequency obviously, the request to do it at variable frequency makes it go from done around once to never AFAICS).Sloan made his generator for linear accelerators, but modern accelerators use cavity resonators, not solenoid coils. Great Q, bit big at these frequencies.

author: ebastler
author_rank: Super Contributor
timestamp: November 12, 2023, 07:21:29 am
content: Quote from: adras on November 11, 2023, 08:37:05 pmI think this is the heart of the problem. This approach has led you to a set of specs where each spec might be achievable individually, but only with major compromises on other aspects. You are aiming to build a race car which can also be used as a truck, and sets a new record in low fuel consumption at the same time.Thinking your planned experiments through in more detail, and defining which requirements you need to be met in combination vs. which ones can be split out and met by a different generator, seems like the way to go. I trust that you won't need 50 separate devices...

author: adras
author_rank: Regular Contributor
timestamp: November 12, 2023, 01:40:50 pm
content: Alright, let's try the following. Instead of working against me, by telling me what's not possible, how about you work with me and tell me what's possible.Because all I hear is: It's impossible! Yet if you just tweak one of my specs it quickly becomes possible. Generating a megavolt with 300Watts, how about a marx generator? Still copper losses? How about a single spark once every 3-10 seconds, still impossible?

author: ebastler
author_rank: Super Contributor
timestamp: November 12, 2023, 02:19:39 pm
content: Quote from: adras on November 12, 2023, 01:40:50 pmI don't see how warning you away from an ill-conceived idea would be "working against you".Personally I am not interested in high-voltage stuff myself, and don't claim to be an expert at all. Hence I'll leave it to others to suggest realistic specs and implementation ideas (which some have already done),ifthey feel like "working with you".

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 12, 2023, 02:36:29 pm
content: Quote from: adras on November 12, 2023, 01:40:50 pmHow about we try this:What are you really after? What are you really interested in?It's okay to say something hokey like, make bright flashy noisy sparks. It's sensory input, it's shiny, it's dramatic. The appeal is simple and broad. Nothing wrong with that. No need to be cryptic.Then we can science it. What kind of sparks do you want? How big? How often? What kind of excitation (volts, amps, frequency, power) leads to what kind of sensory experience?We can take this quite far. You can literallylisten to sparks. It's not a great transducer, but, the concept is there.If you want big boomy sounds, you'll need large sparks and low frequencies; stuff like mains arcing, that'll require big power. But at least it won't require complicated circuitry, or violating physical laws.If you want sharp, ear-splitting reports, capacitor discharge is the way to go. Marx generator? No problem. Higher energy leads to thicker sparks and louder reports, but higher voltage doesn't necessarily lead to a "meatier" sound: the duration of a high-voltage spark can be fractions of a microsecond; consider a slower discharge, done by increasing the loop inductance and/or resistance. A discharge in the ~ms range will have significant mid-audio-frequency output, and feel more substantial than an extremely short one where most of the energy isn't even audible.In most all cases, more energy into the plasma means more sound and light; you need to avoid internal resistance to the extent it robs the circuit of plasma energy. This is why lossy photoflash capacitors for example, don't deliver as loud a report as snap-in low-ESR types. But you also need to be careful not to damage the capacitors doing the work; electrolytics don't tolerate reversal (and they aren't very fond of rapid discharge anyway, though you can get away with it for some, oh who knows, hundreds of pulses say, if you just want to see what it's like).High voltages aren't strictly required. Low voltages can make significant sound from the vaporization of contacts; some of the loudest electrical sounds I've heard were from either discharging a rather modest size capacitor in a confined space (a room), or the explosive failure of semiconductors (the die and bondwires instantly turn to plasma, propelling the plastic package apart; eye protection strongly encouraged!!). The output in this case can be, not just expanding air (rapidly heated to plasma), but vapor and smoke from the device being discharged. Small wires can be fused at such a rate that the metal vapor expanding causes sound and heat output, and a little extra voltage can ionize that track for additional heat and light.If you want more of a plasma torch setup, high frequencies are suitable for that. Air takes time to deionize (recombine), or cool down; in that time, if more energy comes in, the plasma channel stays active, and a continuous arc, or glow discharge, occurs. The sound/light output is similarly smoothed over between cycles; you could have a tone-burst excitation for example, where a pulsed amplifier delivers say some ~kW for some ~ms, giving a similar experience as a mains-frequency spark but without the massive transformer otherwise required for that, nor the high-voltage high-energy caps that would be required to produce an analogous discharge as a single (unipolar) pulse.What isn't science, is pulling numbers out of thin air and asking blindly about them, not making any reciprocation of knowledge, or effort on your part to even mildly reality-check it. That's actually a good way to make a lot of people annoyed, and disinclined to answer your further questions -- including if/when those questions become more reasonable, when people would otherwise be interested to give replies to them.Tim

author: Marco
author_rank: Super Contributor
timestamp: November 12, 2023, 03:24:54 pm
content: Quote from: adras on November 12, 2023, 01:40:50 pmHigh voltage pulses are obviously easier, but a MHz rep rate is pretty much unheard of.

author: TimFox
author_rank: Super Contributor
timestamp: November 12, 2023, 03:34:33 pm
content: A Marx generator is good for generating a high-voltage pulse, but you wanted programmable signals at high repetition rates.

author: Marco
author_rank: Super Contributor
timestamp: November 12, 2023, 05:43:59 pm
content: Quote from: adras on November 12, 2023, 01:40:50 pmI think the pulse driven Tesla coil I mentioned is probably easiest to build, you can build it entirely under oil whereas with a Marx you have to worry about the spark gaps ... under air a MV range device gets a bit big.https://www.semanticscholar.org/paper/A-Compact-Battery-Powered-Half-Megavolt-Transformer-Sarkar-Braidwood/19068167ba56444380eaa8b482ffc5dd4067de14You might even be able to drive it with a massive half bridge instead of a pulse, for a millisecond or so before it needs to cool down (also lets the half bridge cool down, because it probably won't be exactly ZVS).

author: Vovk_Z
author_rank: Super Contributor
timestamp: November 12, 2023, 06:28:14 pm
content: Quote from: ejeffrey on November 10, 2023, 12:40:02 amSo it's just 17 one-attofarad capacitors connected in parallel.

author: MarkT
author_rank: Frequent Contributor
timestamp: November 12, 2023, 07:04:14 pm
content: Quote from: adras on November 12, 2023, 01:40:50 pmWhat's your budget? Large TV transmitters can do perhaps 100kV at 100MHz sort of thing (most of that voltage is developed by the resonance of the antenna), but even the cooling system for something like that is hugely expensive - and you need the transmitting licence, a large plot of land, 100kW or more electrical power... You can't rewrite physics to suit you!

author: adras
author_rank: Regular Contributor
timestamp: November 13, 2023, 07:51:49 pm
content: Quote from: T3sl4co1l on November 12, 2023, 02:36:29 pmWhat a great reply. I can't tell you what I'm looking for. I don't even exactly know what I'm looking for, that's the reason why I want to experiment.I've got two signal generator boards here: ADF4351 + AD9833. I would like to know to which amount we can boost the voltage while keeping the signal alive.In the meantime, I guess I'll figure out how to connect both of them nicely to a microcontroller. The AD9833 so far works great with an arduino, but I think I've got a NodeMCU with a display lying around

author: Marco
author_rank: Super Contributor
timestamp: November 13, 2023, 10:23:19 pm
content: If you really want arbitrary signals, then it's just a question of building the highest voltage class A or AB amplifier practical (so substantially below 100kV, not a MV).

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 14, 2023, 08:47:40 am
content: Quote from: adras on November 13, 2023, 07:51:49 pmtry boosting it to mains voltage level first (100-240V) and see if you can manage (dream little first), if you succeeded then you can dream a little more, 10X or 100X more the output. gate capacitance is too much when entering MHz region the last time i tried but... i never tried hard enough. cheers.