Before you buy a DSO138 or DSO150 from eBay, Amazon, wish or Ali Express, it is important to understand what you are getting. The specifications are very loosely written and what looks good on paper is useless in practical use. Here I test the DSO138 specified at 200 kHz, but in reality it is worthless above 20 kHz.
Buying the right oscilloscope is knowing your work area limits and where it might be in the future. I recommend that you read: 12 things to consider when choosing an oscilloscope: https://www.mouser.com/pdfdocs/Tektronix12_things_to_consider1.pdf
For the Nyquist applet to play with: http://195.134.76.37/applets/AppletNyquist/Appl_Nyquist2.html
Hello
The BW testing should be done with a compensated probe, adjusted to the specific input capacitance or with a 50 Ohm termination on the input BNC. If not the capacitance of the leads are causing the signal distortion.
Hi Eyal Hemed
Are you seriously telling me that the performance you see here is due to lack of a compensated probe, which is not supplied with the kit, and has nothing to do with a inadequate ADC in the front end?
Kind regards
Mads