Please excuse if this is stupid, I've been searching to see if I can find an answer to this on Google, but it seems I'm facing the issue in which I don't know how to describe the issue I'm trying to solve.

I'm using a function generator to generate a square wave with 100mVpp, I'm using the oscilloscope, without a breadboard, to read the signal from the function generator.

My understanding is that an oscilloscope reads the voltage changes and displays it on a time series. However, as you see in the picture below, I have two lines for each peak.

Why are there two lines? Does it represent a range?

enter image description here

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    \$\begingroup\$ Try changing the time scale to a much higher value (i.e. slower timebase) you probably have some low-frequency interference and you are seeing the combination of the two. Also if you ever suspect the scope connect the probe to the scope calibrator output - it will give you a known frequency and amplitude square wave to verify it is working correctly. \$\endgroup\$ – Kevin White Jun 25 '19 at 17:06
  • \$\begingroup\$ Does the trigger level change it from 14mV to 0V? You have 20mV of CM noise superimposed. Bad gnd? Also uncalibrated probe with 5% sag. Try coax cable 50 OHM load for textbook waveforms. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 25 '19 at 23:23

Why are there two lines? Does it represent a range?

No, it means you have persistence turned on on the scope. What is happening is the same signal is riding on another signal that is moving it up and down. The scope is showing many different triggers on the same frame. Turn persistence off or single trigger. Try using single triggering, and then keep single triggering.

You may also want to look at your ground and how the signal is coupled to the oscilloscope. IE: DC vs AC coupling.

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  • \$\begingroup\$ It’s says Normal Mode for acquisition, not persistent mode. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 25 '19 at 22:57
  • \$\begingroup\$ On Tek scopes they call it persistance, whatever you want to call it, the scope is graphing the last few triggers. \$\endgroup\$ – Voltage Spike Jun 25 '19 at 23:00

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