Diy rf power amplifier for experimental use - Page 1
Forum section: electronics / beginners

author: Mm
author_rank: Contributor
timestamp: August 23, 2023, 05:47:29 am
content: Im looking for most affordable and efficient way to amplify single square wave frequency. The frequency is between 1mhz to 10mhz. Best would be that the amplifier have potentiometer/trimmer to adjust the amplification. Input signal is weak, less than 1W and the amplifier should be able to amplify the signal at least to 100W or even more. If possible, input power supply could be flexible between 9-60V (which then affects to the output amplitude of the signal).I hope this makes any sense. What kinda options do I have? I have friends who can help me out with making PCBs and soldering all parts together, but they have less experience from radio tech, so I have to try figure out with help of internet how this should be done.This amplifier is used in very experimental device and it is not used at all in conventional way. Signal generator creates the signal, the signal gets amplified and then it is transmitted to resonator circuit. No radio is used at all.I have searched in aliexpress but havent found any good solutions yet.Something like this:https://a.aliexpress.com/_m0mNNRYAny help is appreciated. Thx

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 23, 2023, 06:58:34 am
content: Is 1-10MHz the squarewave's full bandwidth, or its fundamental in which case what rise/fall time do you need?"Less than 1W" isn't exactly "weak", but if you need 40dB gain, fair enough.Since it's square, surely you would need a (fast) switch, more so than an amplifier (implying linearity, proportionality, and generally, poor efficiency)? That is, an inverter?Is this like a piezo driver or something?Tim

author: Mm
author_rank: Contributor
timestamp: August 23, 2023, 07:44:59 am
content: Thx for replying and expressing interest.The frequency is going to be one frequency between 1-10mhz at given time. The resonator where the signal, after being amplified, is transmitted will be changed between experiments and that determines the frequency (which is always just one specific frequency with the resonator/experiment).Im experimenting one specific phenomena with zpe device and for that I need to be able to test how signal amplitide affects to the outcome after resonant frequency is found. So, basically I have experiment where I have certain type of resonator and I transmit signal to it. If the signal is correct (resonant frequency) I get very specific and wanted outcome, but that is with very narrow amplitude scale of the signal. Now I would like to experiment way wider amplitude scale.I do not have budget to buy expensive signal generator amplifiers, but Im hope Im able to build one. The amplifier can be very crude (no fancy stuff needed).

author: mikerj
author_rank: Super Contributor
timestamp: August 23, 2023, 08:06:54 am
content: Quote from: Mm on August 23, 2023, 07:44:59 amA square wave has a lot of energy in the odd harmonics (e.g. 3x, 5x, 7x, 9x the fundamental). If you try to pass a 10MHz square wave through an amplifier with a -3dB cut off around 10MHz then you'll get something like a distorted sine from the output as all the harmonics will be significantly attenuated. Hence the question about whether 10MHz is the fundamental frequency of the square wave, or it's bandwidth.If you want to amplify a 10MHz fundamental square wave and keep it looking like a square wave then you will need considerably more bandwidth from the amplifier, the exact amount depends on how fast you need the rising and falling edges to be.

author: Gyro
author_rank: Super Contributor
timestamp: August 23, 2023, 08:12:38 am
content: Quote from: Mm on August 23, 2023, 07:44:59 amThis is probably a good time to note the importance of correct use of case. 1-10mHz is milliHertz. T3sl4co1l and mikerj interpreted and corrected this to 1-10MHz (MegaHertz) but you repeated the error. Such things are important to avoid confusion, particularly if RF isn't mentioned anywhere in the text or title as a clue.

author: Mm
author_rank: Contributor
timestamp: August 23, 2023, 08:20:11 am
content: Im not sure if this helps at all, but my estimation is that that frequency Im going to be using is 1-5mhz in each experiment. The bandwidth that the amplifier can amplify can be much more broad if it helps with this.About how fast rise/fall can and should be is still a mystery. Im sure slower rise/fall is acceptable at this point.

author: gbaddeley
author_rank: Regular Contributor
timestamp: August 23, 2023, 08:41:48 am
content: Why do you need a square wave?Is an approximate square wave OK? (Limited harmonics, ringing, limited slewing)Sine wave is not suitable?

author: Mm
author_rank: Contributor
timestamp: August 23, 2023, 09:04:11 am
content: So far square wave has given the best results in my experiments, but approximate square wave is ok too at this state

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 23, 2023, 09:50:39 am
content: Ah.....Quote from: Gyro on August 23, 2023, 08:12:38 am...If they're "working" with "ZPE" (Zero Point Energy?) devices, somehow I don't think it will matter.This also explains the budget limitations.Tim

author: Mm
author_rank: Contributor
timestamp: August 23, 2023, 10:11:17 am
content: Quote from: Gyro on August 23, 2023, 08:12:38 amOh, sorry I missed your reply. You are right, Mhz is used not mhz. My bad.

author: Mm
author_rank: Contributor
timestamp: August 23, 2023, 10:13:16 am
content: Quote from: T3sl4co1l on August 23, 2023, 09:50:39 am

author: wasedadoc
author_rank: Super Contributor
timestamp: August 23, 2023, 10:56:35 am
content: Quote from: Mm on August 23, 2023, 10:11:17 amYou still have not got it quite right. MHz, not Mhz.

author: Mm
author_rank: Contributor
timestamp: August 23, 2023, 11:17:05 am
content: Quote from: wasedadoc on August 23, 2023, 10:56:35 amThat is true. My bad. MHz

author: David Hess
author_rank: Super Contributor
timestamp: August 24, 2023, 09:13:26 am
content: Quote from: Mm on August 23, 2023, 05:47:29 am10 MHz at 100 watts is a serious design challenge. I have achieved 600 kHz at 25 watts but that was with 2 MHz output transistors. A discrete implementation of a current feedback amplifier should be able to achieve what you want using ring emitter transistors or MOSFETs in the output stage.

author: gbaddeley
author_rank: Regular Contributor
timestamp: August 24, 2023, 09:22:38 am
content: Have you considered the broadband RFI that it will produce? Are you operating inside a Faraday cage or similar?

author: Mm
author_rank: Contributor
timestamp: August 24, 2023, 10:24:23 am
content: Quote from: David Hess on August 24, 2023, 09:13:26 amDo you have any examples of this? Thx for your reply

author: Mm
author_rank: Contributor
timestamp: August 24, 2023, 10:46:34 am
content: Quote from: gbaddeley on August 24, 2023, 09:22:38 amI understand your consern. This is kinda thought of. The device will be eventually shaped and build in the way that possible RFI is reflected back in and hopefully used in our advance. How much RFI it will be emmitting is still a question because I do not know, at this time, how much amplification is needed for this particular signal, if needed at all. Other high frequency signals going through this device are so low in amplitude that RFI is most likely not be a problem.

author: Infraviolet
author_rank: Super Contributor
timestamp: August 24, 2023, 01:30:13 pm
content: 60V and 100W are pretty big, but...For smaller signals I've had success using common emitter transistor amplifiers to amplify voltage, and an NPN can trivially serve as a buffer to increase the current capability of an analog signal (at the expense of losing about 0.6V). Maybe you could find a high enough power transistor to handle your requirements.I had a thread recently about amplifying a sine signal at 3MHz, I needed to get an output at the end of it which was linearly proportional to the input voltage, and having abit of extra current driving capability (low impedance source) than the original input was somewhat needed too.Do you need to amplify in this manner, where the voltage of the input signal linearly controls the voltage of the output, or are you in a more "comparator like" situation, just send the output as igh as possible when input is above a threshold and as low as possible when below a threshold?There's a youtube channel which has some good videos about transisot amplifiers, mostly focused on audio but the discrete transistor methods should work fine up to 10s of MHz. Not sure if this will still apply at high power, but high power rated transistors do exist, some are probably similar in speed performance to typical low powered ones.https://www.youtube.com/@TheAudioPhool/videos

author: Mm
author_rank: Contributor
timestamp: August 24, 2023, 02:23:01 pm
content: Quote from: Infraviolet on August 24, 2023, 01:30:13 pmThx for taking your time and answer to me.At the monent I need amplifier so I can play and tweak the signal more freely. Im building a prototype of zpe device, but atm I need dev amplifier to have understanding do I even profit of using amplification and if I do profit from it, how much do I need to amplify the signal. Purpose of this dev amp is to find "sweet spot" and after finding it, develop the actual amp for the protype device itself (if it is needed). Most likely the actual amp is easier to dev knowing more parameters than I know at this point (which is kinda zero).There is naturally other things I need to take in consideration too, like impedance, SWR etc..The point is to have somekinda understanding, would amplifying the signal effect the output. There is no information out there that I can use to know this before testing it myself. How the signal power can effect the output? Will the output increase at all after amplifying the signal? Is the possible output increase linear to the amplification? Is there samekinda "sweet spot" like there is with frequency (resonant frequency)? And many other questions is in my mind. Crude/simple amp would give alot of answers.

author: David Hess
author_rank: Super Contributor
timestamp: August 24, 2023, 03:22:26 pm
content: Quote from: Mm on August 24, 2023, 10:24:23 amThe closest available examples I know of are older 40+ MHz function generators from Tektronix and especially HP which use a suitable output amplifier but not to that power level.I would design such a thing from scratch as something similar to a traditional class-AB audio amplifier, but with the output stage configured to use local current feedback which is typically not done in audio designs.

author: TimFox
author_rank: Super Contributor
timestamp: August 24, 2023, 04:01:39 pm
content: When dealing with square waves, the rise time is an important parameter along with the fundamental frequency.

author: tggzzz
author_rank: Super Contributor
timestamp: August 24, 2023, 04:53:23 pm
content: Quote from: T3sl4co1l on August 23, 2023, 09:50:39 am... and thecontinuedignorance of SI units... and thecontinuedlack of information about the rise/fall time in favour of "square wave".The OP might learn why rise/fall time is relevant by looking at the practical measurements (plus a little theory) athttps://entertaininghacks.wordpress.com/2018/05/08/digital-signal-integrity-and-bandwidth-signals-risetime-is-important-period-is-irrelevant/Everybody else here already knows that!

author: magic
author_rank: Super Contributor
timestamp: August 24, 2023, 05:46:02 pm
content: Why even think about amplifying square waves?Get a variable switching PSU to set output amplitude (or spend your 100W heatsinks on making a linear regulator), then switch the load between supply and ground with a pair of complementary MOSFETs. It's still some work to make fast gate drivers, and getting the dead times right is highly advised, but sounds an order of magnitude easier than a linear amp with such capabilities

author: Mm
author_rank: Contributor
timestamp: August 24, 2023, 06:07:54 pm
content: Quote from: tggzzz on August 24, 2023, 04:53:23 pmJeez, no need to yell. What triggered you so badly? Im happy for you that you know your theories.Little quote from "NEWBIES PLEASE READ BEFORE POSTING" post:"Regulars, please be extra nice to beginners asking questions. Do not deride them for anything, if you can't be nice, don't post."I have not said at any point that Im expert in this field, hence Im writing at the "Beginners" section, have you noticed it? Actually Im very very novice with electronics and specially with ham radio stuff, I have no problems admitting these facts.I already apologized and admitted my unit error, what else you want? I dont see any point to start give reasons why my SI unit mishaps happened, you can think what ever you want of it...and I said also this "Im sure slower rise/fall is acceptable at this point.". Im not trying to achieve 90 degree angles on the square wave, I said few times already that the amp can be crude and simple, no fancy things is needed. I did not add ns value for rise/fall but I did not ask complete solution for the amp either.And yes, 100W is most likely overkill and too hard to achive. Maybe 50W is better and still it might be too hard to achieve.

author: langwadt
author_rank: Super Contributor
timestamp: August 24, 2023, 06:11:02 pm
content: Quote from: magic on August 24, 2023, 05:46:02 pmmight try two of these in a bridge,https://www.ixysic.com/home/pdfs.nsf/0/6AC7CC624179BDA185257873005D6BE4/$file/IXD_630.pdf

author: Mm
author_rank: Contributor
timestamp: August 24, 2023, 06:16:31 pm
content: Here is example pic of the "square" wave atm. It is not pretty and hardly even recognizable. Atm Im not after the most perfect square wave.2 channel (blue) represents the input signal.1 channel (yellow) represents the output - can be ignored atm.

author: Mm
author_rank: Contributor
timestamp: August 24, 2023, 06:18:44 pm
content: Quote from: magic on August 24, 2023, 05:46:02 pmThx for this, I really appreciate your help with this.

author: Mm
author_rank: Contributor
timestamp: August 24, 2023, 06:19:50 pm
content: Quote from: langwadt on August 24, 2023, 06:11:02 pmThx mate

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 24, 2023, 09:09:01 pm
content: That more or less confirms what I suspected, a resonant application where the harmonics don't matter.FYI, this would've been excellent information to include in the initial post, or a schematic suggestive of same.That leaves the question of phase, as when an inductive phase (even slightly) is guaranteed, a switching circuit like half-bridge can operate very efficiently indeed; running silicon MOSFETs that fast may be a challenge (short of proper RF types $$$), but GaN are available these days which can do that no problem. Downside: GaN are faster and tinier than ever: the slightest misstep, poof, they're melted blobs of semiconductor on the board (so the board is probably toast, too).If you're "experimenting" with a resonant circuit, then it's likely you'll be doing things that shift the resonant frequency, and therefore the phase seen by the inverter. A phase detector might be used to provide protection, or to adjust frequency to stay just above resonance.It may simply be acceptable to run Si MOSFETs that fast, even fairly old ones (IRF540?), and accept the high switching losses (big heatsink) even when unloaded, off resonance, or below resonance (non-inductive phase).Tim

author: Mm
author_rank: Contributor
timestamp: August 25, 2023, 09:39:11 am
content: Quote from: T3sl4co1l on August 24, 2023, 09:09:01 pmThx, mosfets seems to pop up in many suggestions here and elsewhere on the internet.

author: dietert1
author_rank: Super Contributor
timestamp: August 25, 2023, 10:21:51 am
content: In many western countries running a RF circuit at 30 MHz and at a 100 W or so power level is subject to legislation. Be shure to avoid trouble to your neighbours and yourself.You can probably make that aliexpress amplifier into something useful by adding a fan, a solid metal enclosure, a mains power supply, a sampling circuit to monitor the ouput level and/or SWR meter and some good RF cables. Also you will need a preamplifier to go from 1 W to 70 W in two steps. That setup requires some work and it won't be cheap.Regards, Dieter

author: Mm
author_rank: Contributor
timestamp: August 25, 2023, 02:25:51 pm
content: Quote from: dietert1 on August 25, 2023, 10:21:51 amIm aware of this, but I appreciate your take on this.

author: Mm
author_rank: Contributor
timestamp: August 25, 2023, 02:32:08 pm
content: What if my signal would be sine wave and output signal should be only max 30W?What would be easiest way to achieve this? Simple class AB amp?

author: langwadt
author_rank: Super Contributor
timestamp: August 25, 2023, 02:40:12 pm
content: Quote from: Mm on August 25, 2023, 02:32:08 pm30W into what impedance?

author: Mm
author_rank: Contributor
timestamp: August 25, 2023, 06:15:40 pm
content: Quote from: langwadt on August 25, 2023, 02:40:12 pmSorry, but there is no one answer to that. Im going test with multiple resonators which all have different resistance and therefor impedance changes too. But impedance is on the low side on all of the cases

author: tggzzz
author_rank: Super Contributor
timestamp: August 25, 2023, 07:42:41 pm
content: Quote from: Mm on August 25, 2023, 06:15:40 pmLow side of what? 0.1ohm? 4ohm? 8ohm? 50ohm? 75ohm? 600ohm, 10Mohm?Prof David MacKay called the first section of his remarkably good book "Numbers Not Adjectives" for very good reasons. "Without Hot Air"

author: TimFox
author_rank: Super Contributor
timestamp: August 25, 2023, 07:53:07 pm
content: Please note that normal "AB" amplifiers are essentially voltage sources with finite current capability.The power rating is different for 4 ohm or 8 ohm loads.For your non-resistive load, you need to specify a range of voltage and current required.

author: YqHFXa01
author_rank: Newbie
timestamp: September 03, 2023, 02:14:09 am
content: Quote from: Mm on August 23, 2023, 05:47:29 amIt's simple and efficient, but some of the components aren't cheapYou can reduce the power of the input power supply to meet the usage requirements