Diy rf power amplifier for experimental use

[Mm]

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.

[Mm]

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

Thx for this, I really appreciate your help with this.

[Mm]

might try two of these in a bridge, https://www.ixysic.com/home/pdfs.nsf/0/6AC7CC624179BDA185257873005D6BE4/$file/IXD_630.pdf

Thx mate

[T3sl4co1l]

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

[Mm]

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

Thx, mosfets seems to pop up in many suggestions here and elsewhere on the internet.

[dietert1]

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

[Mm]

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

Im aware of this, but I appreciate your take on this.

[Mm]

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?

[langwadt]

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?

30W into what impedance?

[Mm]

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?

30W into what impedance?

Sorry, 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

[tggzzz]

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?

30W into what impedance?

Sorry, 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

Low side of what? 0.1ohm? 4ohm? 8ohm? 50ohm? 75ohm? 600ohm, 10Mohm?

Prof David MacKay called the first section of his remarkably good book[1] "Numbers Not Adjectives" for very good reasons.

[1] "Without Hot Air"

[TimFox]

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.

[YqHFXa01]

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/_m0mNNRY

Any help is appreciated. Thx

It's simple and efficient, but some of the components aren't cheap
You can reduce the power of the input power supply to meet the usage requirements