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I'm trying to figure out what exactly I need in order to amplify a power of an analog signal, generated using a function generator (in the range of 100 kHz - 4 MHz, with the max voltage output of 7V), in order to send it to an antenna (50 ohm), so the output signal has around 50 watts in power.

I suppose I need to use an amplifier, but I'm not sure should it be an op amp, a power amp or something completely different.

Researching has lead me to amps like: OPA455, OPA462, OPA552 or LM675 (from TI search page), but I'm not sure if I'm on the right track. Are those the kind of amplifiers I need?

I guess I also need a DC power supply of around 50V if I want to achieve 50 watts with an amplifier (50V * 50V / 50 ohm == 50 watts)?

Also, is there any readily available device/kit that does this amplification already, so I can avoid crafting an amp myself (and introducing a potential hazard point)? :)

Any information is welcome, in form of comments, links, etc.

Just to clarify some things, I'm not trying to building any kind of a radio station and the device itself will probably be enclosed in a Faraday's cage of sort, to avoid any legal issues and interference with local radio stations.

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    \$\begingroup\$ Beware of the laws in use ... Some thing as this ? ebay.com/itm/… \$\endgroup\$
    – Antonio51
    Commented Sep 18, 2021 at 9:52
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    \$\begingroup\$ Your guess about the DC supply voltage is wrong. Assuming a sine wave and one ideal amplifier, you will need a +71 V supply and a -71 V supply. Not to mention the difficulties in designing an antenna for 100 kHz \$\endgroup\$
    – jonk
    Commented Sep 18, 2021 at 10:33
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    \$\begingroup\$ @MladenB. Yes, RMS. Keep in mind that you are discussing sine waves (or cosine waves -- doesn't matter) and that the effective power is a factor of \$2\sqrt{2}\$ relative to peak to peak voltage. In short, \$50\:\text{V}_\text{DC}\$ power supply implies \$50\:\text{V}_\text{DC}\cdot 2\sqrt{2}\approx 141\:\text{V}_\text{PP}\$. If you take the center of that as zero, then you wind up with the rails I mentioned. But on top of that, you will need overhead voltage that is used for control. So I'd figure about \$\pm 75\:\text{V}\$, plus ground. At minimum. I'm still wondering about the antenna. \$\endgroup\$
    – jonk
    Commented Sep 19, 2021 at 6:55
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    \$\begingroup\$ @MladenB. Well, a 25 V DC supply with a programmable load of 2.9 A is, in fact 72.5 W. But that's a DC supply. Not an AC one. Once you shift from DC to AC, you are in a different ballpark. \$\endgroup\$
    – jonk
    Commented Sep 19, 2021 at 7:51
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    \$\begingroup\$ This can help ? cache.nxp.com/docs/en/application-note/AN593.pdf \$\endgroup\$
    – Antonio51
    Commented Sep 19, 2021 at 9:39

1 Answer 1

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How to explain that you can increase power ... with low voltages, and increase also voltage ?

https://cache.nxp.com/docs/en/application-note/AN593.pdf

With the use of HF transformers, one can add the power of low level power generators and so, increase the voltage on the load.

This simple one ...

enter image description here

Now, consider this schematic (well known from HAM radio), this will help to understand the principle.

enter image description here

The generators are opposite in voltage (10 V peak).

On the load, one can see that the voltage (35 V peak) is ... higher than the generators themselves.

The efficiency of this operation depends on the impedance of the generators. (lower graphic). Here 86 % efficiency.

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  • \$\begingroup\$ Thank you for these schematics. Btw, where does the excess power come from? Are some of transformers in resonance or something? \$\endgroup\$
    – Mladen B.
    Commented Sep 20, 2021 at 7:42
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    \$\begingroup\$ The transformers are "ideal". So wideband ... There is not excess power. The powers are given by the 2 generators. Transformers simply "reshape" the output voltage using the two generators. There are just losses here in the internal resistance of the generators. The first assembly to a single transformer is obvious (just as a "H-bridge"). This is a trick often used in audio amplifiers (linear or digital). The other is a little more complicated to explain ... I use ... in simulation, I haven't tried to explain yet. :-) \$\endgroup\$
    – Antonio51
    Commented Sep 20, 2021 at 8:11
  • \$\begingroup\$ I see, thanks for a bit more clarification. So, I guess, V1 and V2 need to have their phases in sync? Also, I guess this is the way to combine smaller power supplies into a stronger one, which can then be used with a specific amplifier to actually amplify the source signal? If I get those 2 schemes correctly, we're essentially just increasing the voltage using transformers, but we don't amplify the output power. Is that a correct assumption? \$\endgroup\$
    – Mladen B.
    Commented Sep 20, 2021 at 8:48
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    \$\begingroup\$ @Mladen B. "So, I guess, V1 and V2 need to have their phases in sync?" Yes, (180°) but it is not to difficult. See in the note how the two signals are "generated". See link in answer fig 1. It is just T2. With one transformer ... "we don't amplify the output power." Yes, just "mixing" through the transformers. \$\endgroup\$
    – Antonio51
    Commented Sep 20, 2021 at 8:58

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