I just bought this scope, a Picoscope 2405A, and my first real oscilloscope. I've been playing around with it to get familiar with the features. It has a signal generator built in, and I wanted to see how well the scope works at high frequencies. The scope is supposed to have 25 Mhz bandwidth. But the signal generator only goes to 1 Mhz, and I don't have any way of generating a higher frequency with a known waveform.
So I hooked up the scope to the 1 Mhz square wave, and I was a little disappointed to see that it was pretty distorted. In fact the highest frequency that looks anything like a square is a few hundred Khz. But some rounding off is to be expected, after all, it can't show all the harmonics since it's limited to 25 Mhz anyway right? I know the theory of this, but I'm short on experience, so my problem was, I didn't know how to tell *how* distorted a 1 Mhz square wave should be on a scope with 25 Mhz bandwidth. Then I had an idea - the software has a spectrum analyzer feature. Could that tell me exactly how much harmonics I'm picking up, and thereby show me the true limit of the scope's bandwidth? I thought this would be a valid test, since the spectrum analyzer is just a software feature and can only display information that the scope has successfully picked up.
Here's what I got when I tried it out (see attached pic).
The 25 Mhz peak is actually fairly distinct, and in fact the 27 Mhz one is visible too. After that it's just noise.
So I take that to mean, my funny looking signal *is* what a square wave should look like with bandwidth limited to 25 (or maybe 27) Mhz. Is that right? (Not that I had any reason to doubt the specs, but I just like to see things for myself...that's why I have a scope!)