Spec Hack! Breaking the Bandwidth Barrier with Your Oscilloscope

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Video covering bandwidth basics: https://youtu.be/T56XDhUyY2g

The DSOX1204G scope we used: https://www.keysight.com/en/pdx-2969966-pn-DSOX1204G/oscilloscope-70-100-200-mhz-4-analog-channels?cc=US&lc=eng

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We all know that the goal of an oscilloscope is to take the signal on your device, and accurately represent it on the screen. All of the scope advice and how-to info out there is centered around this idea.

But, what if you don’t care about getting an accurate representation? What can you do?

Today we’re going to push the traditional boundaries of an oscilloscope with what I like to call a “spec hack.” It’s not a normal “hack,” it’s more of a creative way of pushing your gear beyond what it could normally do. Throughout history, we as humanity have pushed the limits of our tools – just because we can. Think about lawnmower racing or mountain biking. Tools used for yard maintenance or transportation have been expertly modified into something that behaves in a new way.

So I got to thinking, what could you do with a scope if you didn’t care about getting a great signal reconstruction?

And this occurred to me. If you don’t care about good reconstruction you could exceed the bandwidth of your scope! If you aren’t familiar with the ins and outs of bandwidth, check out the video on that topic, there’s a link in the description – but here’s the short version. Any frequency components higher than your scope’s bandwidth will be attenuated. They appear smaller.

But, you’ll still see a signal.

Even though you can’t see the signal as it exists on the device, you can still see it. Which means you can do something with it, or at least learn something from it.

One of the things we can learn is the signal’s frequency. Granted, the frequency components won’t look right, but the actual toggling of the signal up and down will give us frequency information.

All we need to measure that is a good trigger and the frequency counter built into this scope. You could also use the on-screen frequency measurement, but the frequency counter is actually a better fit here because it uses the scope’s trigger circuitry. And here’s where it gets really interesting.

The trigger’s circuitry and signal path is actually separate from the acquisition path. The trigger circuitry gets its own signal conditioning and uses a couple comparators.

Since we don’t care about an accurate reconstruction of our signal, we don’t need to use the signal going into the ADC, we ca ... https://www.youtube.com/watch?v=S8eSDjyRceg