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| Siglent1104X-E versus Square Waves |
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| maddoxhq:
First time poster here. I've had a 1104X-E for about 2.5 years now. Haven't used it a whole lot but finally been kicking myself to get back into things. I started noticing something concerning when I was attempting to measure some low value capacitors and inductors. My 100MHz Siglent doesn't seem to be getting that bandwidth. I've been racking my brain trying to blame myself for it with something I'm missing, but honestly I've got nothing left but to point the finger at the scope itself. When I test the bandwidth with a square wave I reach the -3dB mark around 20MHz, well below the 100MHz. Eventually I found the whole "hack" your scope thing and got into it. I at least wanted to check to make sure it's firmware was set up right and asked it PRBD? It replied with 100M. So then I went ahead and threw it the string to increase the bandwidth up to 200MHz. Asked again asked it and it confirmed I was set to 200M. The problem is (and was) the bandwidth is still sitting at ~20MHz. Wondering if my cheap-o Koolertron 30MHz signal generator was to blame I programmed my working PIC project to output the internal clock (8MHz) to a CLKR pin. I then compared it to the Koolertron. And the results are nearly identical. (the PIC seems to provide a cleaner signal, but doesn't fair as well at 8MHz (the pins have a capacitance anywhere between 5 - 50pF, compared to the scopes stated 15pF). The signal generator seems to do better at frequency precision. So back to the scope. I've defaulted it before I ran these tests so I don't think it's a settings issue. I've got four 100MHz probes, and one 60MHz probe, all the same. Is there anything I might be missing or misunderstanding here? |
| Kean:
Are you using your probe set to 1x? Try 10x... |
| maddoxhq:
Yeah, this was done with the probe set to 1X, I tried 10X like you said and it does seem to help the attenuation. I maxed the signal generator out at 30 and only dropped 30mV 68mV (13%). I have to imagine it drops off pretty quick after 30MHz. I wouldn't say the waveform looks any better though. |
| Kean:
If your signal generator maxes out at 30MHz, then it likely cannot generate a nice square wave all the way up to that frequency. Best to read the specs for your sig gen regarding square waves, and specs for your o'scope probes re bandwidth in 1x and 10x modes. Maybe spend some time watching this video to help fill in some fundamentals. It is long, but in particular check the section I've linked directly to that is relevant. https://youtu.be/8ZKMrzTGxLQ?t=5496 BTW, when you change the probe from 1x to 10x, you need to tell the scope about it - otherwise the displayed voltages will be wrong. |
| Kean:
Not sure which Koolertron 30MHz signal generator you have, but I see this in the specs at https://www.koolertron.com/koolertron-dds-signal-generator-counter-2-4in-screen-display-30mhz-high-precision-dual-channel-arbitray-waveform-generator-frequency-meter.html --- Quote ---Sine Wave: 0~30MHz Square & Triangle Wave: 0~15MHz --- End quote --- I am guessing even 15MHz is a bit ambitious for a clean square wave. |
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