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Archive for December 6th, 2018

JYE Tech DSO150 Oscilloscope vs. Actual Signals

The DSO150 oscilloscope’s specs give a 200 kHz bandwidth, so a 50 kHz sine wave looks pretty good:

DSO150 - sine wave 50 kHz 10 us-div

DSO150 – sine wave 50 kHz 10 us-div

A 100 kHz sine wave looks chunky, with maybe 25 samples per cycle:

DSO150 - sine wave 100 kHz 10 us-div

DSO150 – sine wave 100 kHz 10 us-div

The DSO150 tops out at 10 µs/div, so you can’t expand the waveform more than you see; 25 samples in 10 µs seems to be 2.5 Msample/s, exceeding the nominal 1 Msample/s spec. I have no explanation.

A 10 kHz square wave shows a blip just before each transition that isn’t on the actual signal:

DSO150 - square wave 10 kHz 20 us-div

DSO150 – square wave 10 kHz 20 us-div

At 50 kHz, there’s not much square left in the wave:

DSO150 - square wave 50 kHz 10 us-div

DSO150 – square wave 50 kHz 10 us-div

And, just for completeness, a 200 kHz square wave completely loses its starch:

DSO150 - square wave 200 kHz 10 us-div

DSO150 – square wave 200 kHz 10 us-div

A 10% (-ish) duty cycle pulse at 25 kHz has frequency components well beyond the scope’s limits, so it’s more of a blip than a pulse:

DSO150 - pulse 25 kHz 10 us-div

DSO150 – pulse 25 kHz 10 us-div

The pulse repetition frequency beats with the scope sampling and sweep speeds to produce weird effects:

DSO150 - pulse 25 kHz 100 us-div

DSO150 – pulse 25 kHz 100 us-div

Tuning the pulse frequency for maximum weirdness:

DSO150 - pulse 15 kHz 200 us-div

DSO150 – pulse 15 kHz 200 us-div

None of this is unique to the DSO150, of course, as all digital scopes (heck, all sampled-data systems) have the same issues. The DSO150’s slow sampling rate just makes them more obvious at lower frequencies.

Key takeaway: use the DSO150 for analog signals in the audio range, up through maybe 50 kHz, and it’ll produce reasonable results.

Using it for digital signals, even at audio frequencies, isn’t appropriate, because the DSO150’s low bandwidth will produce baffling displays.

 

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