Re: Measuring output watts with an oscilloscope

James Doyle

My Siglent SDS1102x has switchable 50 ohm / 1 Mohm input impedance.  
The setting in on the main menu - right next to the setting where the Probe parameters are set...

Sometimes a directional coupler is handy to have kicking around too!


On Mon, Jan 20, 2020 at 3:18 PM Jon Reck W8REA <jonathan.p.reck@...> wrote:
I also have a measurement question - please help out an electronics novice...

I would like to accurately measure the wattage my QCX radio is putting out, with and without my brand new 50W amplifier but I do not have a suitable watt meter.
However, I do have a brand new digital siglant oscilloscope that I don't really know how to use yet. The scope does not have a built in 50 ohm impedance input, just the 1 meg ohm.

Best I can figure from the internet, I should place my 10x probe across my dummy load and read the RMS voltage, square it, and divide by 50 ohms. I've done that with my QCX 20 with varying results that I don't trust so I bet I'm doing something wrong. Also, I am concerned that I might damage the scope if I do that with the output of the 50 watt amplifier.

Any pointers?
Jon Reck W8REA

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