RTB, RTM, RTA: Acquire Mode "High Resolution" looses details?

Question

I am doing measurements on a pulse modulated signal. To get more details I use the Acquire Mode "High Resolution". But the amplitude drops when I switch from "Sample" to the "High Resolution" mode, so I am loosing details. What goes wrong here?

Answer

There is no error in the firmware.

"High Resolution" helps to reduce the noise, but it does not provide more details. On the contrary - from several sample points the average is calculated which is in fact a reduction of the resolution. The attached drawing explains the function. With the average calculation the noise goes down. For high frequency signals the sample rate is too low (undersampling) which leads to that effect. Higher frequencies are treated like noise.

For correct detection of the signal it is necessary to select a faster timebase.

The attached screenshots shows an example. The signal is a 13 MHz CW with pulse modulation.

SCR10.PNG: Acquire Mode "Sample" --> everything is correct

SCR9.PNG: same time base as before with "High Resolution" --> the sample rate is too low to detect the 13 MHz signal correct

SCR11.PNG: "High Resolution" with faster time base. The amplitude is almost correct.

Conclusion:

For the Acquire Mode "High Resolution" a faster time base is necessary!

Thank you.

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Your Rohde & Schwarz Team

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