DSO FFT Noise Floor for 100MHz -2dBm (0.5Vpp) sine wave (easy or painful ?)

[rfbroadband]

After my response to the DSO vs SA post, I thought maybe it would be interesting for people to share how easy (or painful) it is to setup their scope to display the frequency response of a 100MHz sine wave at 0.5Vpp trying to get the noise floor as low as possible. I have used many scopes and almost all of them had a terrible FFTs and FFT GUIs and implementations. On some of them (even Agilent), if you don't select the correct combination of parameters (sampling freq, memory depth, number of points etc) the screen simply went blank. If you think this is an interesting experiment, please share your experiences on setting up your scope to display a simple spectral component of a 100MHz signal at 0.5Vpp (-2dBm) in the frequency domain with the noise floor reduced as much as possible. Upload a screen shot.

Attached the screen shot of a R&S RTO scope. Setup was very easy, because the scope FFT mode GUI behaves like a spectrum analyzer...

 

[nctnico]

After some fiddling my TDS744A does ok. When set to high-res, long record length and averaging the FFT results it works albait a bit slow.

[TomThomas]

After my response to the DSO vs SA post, I thought maybe it would be interesting for people to share how easy (or painful) it is to setup their scope to display the frequency response of a 100MHz sine wave at 0.5Vpp trying to get the noise floor as low as possible. I have used many scopes and almost all of them had a terrible FFTs and FFT GUIs and implementations. On some of them (even Agilent), if you don't select the correct combination of parameters (sampling freq, memory depth, number of points etc) the screen simply went blank. If you think this is an interesting experiment, please share your experiences on setting up your scope to display a simple spectral component of a 100MHz signal at 0.5Vpp (-2dBm) in the frequency domain with the noise floor reduced as much as possible. Upload a screen shot.

Attached the screen shot of a R&S RTO scope. Setup was very easy, because the scope FFT mode GUI behaves like a spectrum analyzer...

 

Short comment on RTOs FFT:

There is a big difference between RTOs FFT and a let me say classical DSO FFT. R&S use a DDC (digital downconverting) technique before calculating the FFT and they added their experience from their SAs. So you get a great FFT ... but you have to pay for that...