As far as I know there isn't a way to display power level in dBm on the 3000 X-series oscilloscope. There are,however, a couple other routes you can go.
A) You can use the FFT Math function to determine the power level of your signal (in Vrms or dB).
B) You can drop your signal over a 1 Ohm resisor and use the equation P = (V^2)/R where R = 1 and therefore your power will equal your voltage reading squared. This will give you your power level in Watts, not dBm. To convert to dBm you need to use the equation dBm = log(Power/1mW). Keep in mind that 'Power' in the previous equation must be in the form of mW.
**Important note for Option B above: Make sure your 1 Ohm resistor has a sufficient power rating for your test. If you're dropping 5 Volts accros it then you need a resistor with a power rating of greater than 25 Watts.
Thanks for the tip but it would be much easier if the X3034 did the math when the channel impedance is set to 50 ohms. Most of the measurements that I do are for low level RF testing.
You want to see the time domain POWER waveform? On a LOG scale? Why?
I don't think any scope anywhere does that.
If you get a rectifying Schottky diode, provide a power envelope, but on a linear scale (W or mW).
maybe a power meter would better suit your needs? I believe some can show the time domain waveform like you want, natively. Agilent also recently released this tool:
It's all about convenience. I have an RF power and voltmeter. It would be convenient if I could meaure it on the oscilloscope and not have to drag out another piece of test equipment.
The DSO-X3024 already has a 50 impedance and can measure several parameters including RMS. So why not have a selection for dbm ? It's just math! When the 50ohm impedance is turned off the dbm selection in the measurements menu would be disabled.
Agreed, this would be nice to have. If you can show RMS voltage, which you can, and if you can select a 50-ohm terminator, which you can, then you can show dBm and save the user from having to do the math or table lookup manually.
A) You can use the FFT Math function to determine the power level of your signal (in Vrms or dB).
B) You can drop your signal over a 1 Ohm resisor and use the equation P = (V^2)/R where R = 1 and therefore your power will equal your voltage reading squared. This will give you your power level in Watts, not dBm. To convert to dBm you need to use the equation dBm = log(Power/1mW). Keep in mind that 'Power' in the previous equation must be in the form of mW.
**Important note for Option B above: Make sure your 1 Ohm resistor has a sufficient power rating for your test. If you're dropping 5 Volts accros it then you need a resistor with a power rating of greater than 25 Watts.