FAQs from Rohde & Schwarz

RTB/RTM/RTA - reduce Stop Frequency at FFT

Question

I am evaluating a signal in the lower frequency range, i.e 100 Hz. To see more details I want to reduce the stop frequency of the FFT to see more details.

But this is not possible - the lowest possible frequency is far above I want to set. Is there a possibility to reduce it further?

Answer

Yes - this is possible.

The lowest frequency of the stop frequency depends from the RBW setting. At first the RBW has to be reduced - then it is also possible to reduce the stop frequency of the FFT.

For that enter the setup of the FFT:

RTB/RTM/RTA - reduce Stop Frequency at FFT

Deactivate "Automatic RBW"

Now it is possible to change the RBW setting. Click on "RBW" - a window will open which allows to change the RBW:

RTB/RTM/RTA - reduce Stop Frequency at FFT

After that you can reduce the stop frequency. If you still can not reach the desired frequency, repeat the first step (reduce RBW)