# How to calculate RF power output

I have an RF amplifier (GHz), 50W. Power source 28V. Please tell me how do they calculate output power? I know only 1 method: V^2/r.

So, if I try 28^2/50 I got 15W. But its 50W. Another words, if I have 50W and 50 Ohm load, I need amplitude about 50V. But the power source only 28V. How is it possible?

• It might have a transformer step-up output stage or use a power inverter inside the amplifier. Or. if it's a class C amplifier it can probably produce 50 volts p-p from the output transistor stage. Dec 9, 2019 at 16:43
• Link the datasheet for your amplifier. Dec 9, 2019 at 17:17

There is a matching network between the rf power device and the output which transforms the 20V or so of swing at the device drain to ~50V RMS at the output.

The output is 50R nominal, the drain isn't, and may well in fact be significantly reactive.

In the microwave bands this matching network is often a planar structure printed onto the PCB.

• So, there is only 1 way to know - measure it. Right ? And if I do that I will get amplitude 50V ? So that V^2/R still work ? I will get 50V RMS ?
– Sid
Dec 9, 2019 at 16:50
• If the thing is delivering 50W into a correctly matched 50 ohm load, then by definition there will be 50V RMS across the load. Now measuring that accurately is a pain in the arse at microwave frequencies, even my very expensive HP RF power meter depends on the loads and cables being right and metrology grade RF connectors are Expensive. Dec 9, 2019 at 16:54
• @is often a planar structure printed onto the PCB@ Would like to see that.
– Sid
Dec 9, 2019 at 16:59