It’ll probably come as no surprise that the HP ran circles around the DSO at the higher end of their range but below 25 MHz the $200 DSO held its own quite respectably. From 30 to 50 MHz, the DSO’s displayed trace became increasingly unsteady and amplitude measurements became less accurate.
Above 50 MHz, I wouldn’t trust the DSO any further than I could spit a mouthful of fish hooks.
Here’s a chart of readings at various freqs for both oscopes. Signals were generated with Gigatronics 2420M which has a bottom end of 10 MHz so freqs lower than that were not possible.
Note that as frequency increased, the DSO’s values for both voltage and waveform period had to be expressed as a range rather than a fixed, steady value. At 30 MHz and below, ths DSO was rock steady and agreed with both the sig gen and HP scope in terms of frequency/time.
Voltage readings of the DSO varied more than I would have liked. At 20 MHz, the difference between the DSO and the HP begins to exceed 10%. This may or may not be significant though as oscopes are typically used for signal tracing, not for alignment to specific voltages (although that’s not always the case).
I was happily surprised at the close correlation in freq/time between the two oscopes. My main interest in the DSO is for HF ham radio. From 28 MHz on down, freq accuracy of the scope is very accurate. I should mention here that the voltage and period values were obtained via direct alpha-numeric readout that the DSO’s software provides. As far as I can tell, there doesn’t appear to be an option in the software to display two simultaneous cursors that can be placed on the waveform to measure delta – there’s only one for time and one for amplitude.
There are a good number of options selectable for alpha-numric read-out including pk-pk, rms, minimum/maximum voltage and period, freq, rise time, fall time, pulse width and duty cycle.
Dave AA7EE mentioned the jittery appearance of the trace in my previous posting about this oscope. Under the Aquire>Acquisition menu there is an option to enable an averaging function for the displayed trace. As can be seen, this smoothed out things quite a bit. A value of 0 to 128 can be inserted for averaging – too high a value will result in unacceptable delay of the trace’s response to a given change in input signal but it was easy enough to find a range of values that resulted in a smooth trace with hardly any delay.
Two things I want to test still are the rise/fall time accuracy and the FFT/spectrum analyzer function.
Another time…it’s late!