[Elecraft] OT - PC Oscilloscope Performance

[Howard Ashcraft]

The PC based scopes, such as this have remarkable flexibility.  However, they aren't a good substitute for a general purpose analog scope if you are looking for real-time performance viewing non-repetitive data (noise, glitches, spikes, transients).  They also can respond slowly when taking measurements, which is annoying, although not fatal.

Digital scopes sample the observed signal by converting the signal amplitude to a digital value at some repeated interval.  Between sample intervals, they aren't recording any data.  Unless the sampling rate is quite high, they build up information about the waveform in multiple "passes" and then display the result.  If you are looking at a repetitive signal with no glitches, this is OK as the multiple passes will eventually build enough data points to sufficiently describe the analog signal. But if you want to see what is actually happening in real time, you don't want to be looking at a display built from many repetitive waveforms, but from a single pass and you want to make sure you don't miss events (i.e, you want a very short time between samples).  This requires a very fast sampling rate to obtain sufficient data points to describe the signal.  For example, I have a DSA602A, a very good lab quality digital Tek scope from a prior era.  It has a 1Ghz max bandwidth, but if I want it to perform in "real time", it is about equivalent to a 300-350mhz analog scope.  The DSA602a has a maximum sampling rate of 2GS/s (gigasamples/second) and if I recall correctly, glitch capture in the nanosecond range.  The PC based scopes have much lower sampling rates and, thus, can't capture rapidly changing waveforms. This doesn't make them bad, it is just a limitation that may or may not be important to you.  Analog scopes, because they do not digitally sample the signal, show (limited by the rise time associated with their bandwidth) all of the information in the signal.  Of course, the digital scopes have storage, measurement and waveform analysis functions that analog scopes do not.  The bottom line is that unless you buy a very expensive, very fast, digital scope, they don't really replace an analog scope.

My recommendation would be to get a good, used analog scope, (tons of options) and then look at digital options later.


Howard W. Ashcraft W1WF
hwa_AT_ashcraftfamily.net