[sdiy] Oscilloscope on a Budget 200

[Richie Burnett]

> Why would you need a battery or power bank if you still need USB host to 
> provide the display?

Sorry, I thought it had a built-in screen.  I did a quick Google image 
search for PSO2020 and it turned up a couple of images that looked like that 
scope with an cyan/yellow OLED display in the handle where the white on 
white Hantek logo is.  Obviously they were for a completely different 
product!  My mistake.

> Not only the channel bandwidth should be able to catch HF oscillations, 
> but sampling frequency must be high enough not to be bitten hard by 
> undersampled image.

That is the thing that really seems to get you with cheap digital scopes. 
Aliasing.  We have all manner of oscilloscopes in the teaching labs where 
I'm currently working, and the one thing that separates the Tek, Agilent and 
LeCroy, from the Digimess, Owon, Rigol, Tenma, is their ability to properly 
band-limit signals before sampling them and displaying them.  Some of the 
cheap Chinese copycat models will quite happily show you a 20MHz signal as a 
1kHz signal if you have the timebase set to 100us/div.  That really confuses 
students (>.<)  Conversely the likes of Agilent and Tektronics either show a 
nice shaded smudge of HF, or filter it out completely, but never 
undersampled.

-Richie,