Question
When I use the FFT function on my scope, I sometimes wonder about the sample rate changing with my frequency settings.
What is the calculation base for the Sample Rate of the scope?
What is the calculation base for the sample rate on my R&S RTA / RTM series scope when using FFT?
Answer
The reason for the behavior is that the stop frequency is used as the basis to calculate the sample rate.
We take two times of stop frequency and then choose the next higher sample rate as a fixed value.
Examples:
Stop Frequency is
200 MHz --> 500 MSa/s
250 MHz --> 625 MSa/s (the next HIGHER sample rate from 500 MSa/s on)
1 GHz --> 2.5 GSa/s
Higher sample rates don't make sense as we would just have a higher Decimation Rate with the same Record Lenght.
It also will keep the performance of the scope at the maximal level.
