> >>> You need to be able to *capture* the data in real time, in order to > >>> do a single sweep mode, for non-periodic signals. The processing and > >>> display of that data don't have to be real time. > >> Yes, that is true for some applications, but unless this is a real time > >> spectrum analyzer ($$$$) -- which is useful for some applications such > >> as looking for noise and intermittent distortion -- you are going to be > >> working with a stable periodic wave form. > > > > That was in reply to: > > > >>>> To be more specific, > >>>> a digital oscilloscope displays a periodic signal on the screen and the > >>>> refresh scans rather slowly from left to right. > > > > Single sweep mode is a very useful, often essential, feature for an > > oscilloscope. > > Yes, a one shot scope is a useful device. With analog this was a scope > with a storage CRT. With digital this requires a very fast flash ADC > (perhaps more than one). I think that this is going to be rather > expensive compared to a scanning type D-scope for stable AC signals.
So this "scanning" type would use a A/D with a fast sample time but a long time between samples? It would collect data for a long time, and then calculate a time or frequency domain graph? So what sort of bad things happen when the signal isn't periodic? A time domain graph would be impossible, right? Could you sample for a long time and get a frequency domain graph that would be an average? > The nice feature of one shot D-scopes is that they can record a lot more > data than an analog one -- you can record a lot more data than will fit > on the screen at once. Very nice if the test is time consuming to set up, or worse, if it is a destructive test. And you don't need a storage CRT or camera. Upload the data easily, Remote access. Could be used for automated tests. > This has always been a serious issue with an analog spectrum analyzer. > In theory, it should be a Gaussian distribution. This is not realizable > because it would have to extent to infinity. But even taking a > polynomial distribution, it is still impossible to exactly realize a > band pass filter with that response function. And, the filter also > needs to have linear phase response. So, this -- the scan filter > response shape -- is an important feature and something that is better > in more expensive units. > > I suspect that the band pass response shape in these devices is not > anything near a Gaussian response or linear phase. Does this band pass response shape issue go away with a digital SA? Digital filters class was a long time ago, but IIRC you can get any response you want since it is math. _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
