I am using a 3204 with 50 MHz bandwith and 50 MHz sampling rate for amateur radio purposes. Taking a look at a MHz square wave from a DDS generator gives very strange results. If the signal is not a multiple of the sampling frequency, I got large peaks below and above the base frequency in spectrum analyzer view. At 5 MHz and 10 MHz the peaks disappear and the spectrum looks ok. The same pictures from another DDS.
This seems to be an effect of aliasing. The square wave contains harmonics at 3rd, 5th base frequency and so on. But I was not expecting such a big impact on waveforms and spectrums shown in Picoscope. The view is nearly unusable, for a 3 MHz square wave etc.
Now my questions: Is this normal and do others have the same experience? Will it make sense to put in (generally) an anti aliasing filter (lowpass at 25 MHz) in front of the scope? Is there any built in anti aliasing in the scope itself (like it is in PC soundcards etc.)?
Thanks for your help