Re: Caution - grown men playing with oscilloscope toys

Nick Kennedy

Well, I'm going to have to get a little tutoring from Ed since I just tried FFT on my Rigol for the first time today and haven't got it all figured out yet.

Regarding dB-Vrms, I think that's dB relative to 1 volt RMS.  So if you have your source driving a 50 ohm load, 1 volt RMS gives +13 dBm into the load.  With that value, your scope should say 0 dBm.  So I think you just add 13 to what the scope gives to get dBm.

Does that make sense?

I kinda think the FFT implementation on the Rigol isn't quite as slick as it is on the Owan, or whatever that was.


Nick, WA5BDU

On Tue, Jan 20, 2015 at 4:14 PM, n5em@... [PHSNA] <PHSNA@...> wrote:


I just posted a photo in the Photo's section of an FFT Screen Capture from my Rigol DS1102E.

Note that this waveform is the square wave from a CMOS clock oscillator at 10 mhz.  Notice that the spectum output is rich in odd harmonics, while even harmonics are surpressed.  While the bandwidth of the scope is 100 mhz, the last visible product (in this particular resolution) is the 130 mhz harmonic.  I wish it would display the FFT in dBm, but the only 2 options are Vrms and dBVrms.

This is the K3NHI calibrator I use as a reference for my power meters.

I'm just learning about this so comments are welcome.

73, Ed - N5EM

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