EEVblog #396 - Bode Plotting on Your Osciloscope

Dave shows you a neat trick on how to get a real time frequency response bode plot on your oscilloscope using your function generator. Useful for filter or system response characterisation.

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[CPD-KD-.]

Dave! This is an old video, but I watched it when I was in middle school, now I'm in my third year of EE! You have no idea how much of an inspiration you've been.

[EEVblog]

I get bombarded with comments on an almost daily basis on how crap and annoying my voice is etc. There are so many people out there who think you have to sound and talk in a certain way that they expect. You can't be your natural self, unless it fits in with their narrow view. Screw them.
As humorous as they are, it's gotten to the point were I'm contemplating just blocking and deleting every such pointless hatred filled comment.

[tomaszmazurek]

Wow, this will come in so handy - I recently specifically build myself a mini lab to learn more about audio range filters and was a bit baffled that there are no affordable audio frequency range spectrum analyzers. Now I will know how to solve that problem.

[Worldwidewav]

Thank you so much.  This was a huge help in my Electronic Devices II Class.  We used this for a variety of High-Pass and Low-Pass Filters.  It really saved us time rather then setting each individual frequency and then plotting manually by hand or in excel.  Our instructor is actually making labs to use you technique for the following semesters.  I'd love to see more videos on using the features of the equipment, ie; oscilloscope, wave generator etc in analyzing networks and different elements.  I'm hooked on your Blog!

Thank you again!

[SidheS]

Genius. Exactly what I'm after to try to help get a good intuitive understanding of filters. Thanks Dave!

[thosewhowishb]

Just dropping by to say that this was very very helpful and saved me many a time. Thanks!

[ExStaticBass]

This is a neat trick. I've been doing it a while to set up audio systems for client builds. It works great for tweaking filters for surround systems to have a perfect overlap between the tweeters, midbass, and subwoofers.

[infestd]

I've seen a lot of your videos before, wish I had seen this one earlier. I'm building a 10-Band EQ circuit with gyrators instead of inductors with no idea how to test it. I've built another circuit with just one LC filter for bass. I will try this method to test its correctly working. Thank you for this video!

[rcarendsen]

This is what i never thought off ... I had to measure / test some filters while building phase shifters and compensation filters...

Thank you 😊👍

[gamccoy]

BO - DEE
That is a really interesting trick. I think it is near useless for any qualitative measurement but it does make you think about the way you can extended the reach of your instruments. A good engineer always thinks about the boundaries and you are certainly a good engineer. I loved this video, Dave. Keep it up.

[uvxecqy]

Block 'em Dave. Keep your videos coming. I find them very easy to follow and very educational. Thanks for taking the time to share your knowledge.

[fijabo]

It would have been nice to see the generator sweep set to a log scale on the bandgap filter experiment. I was kind of expecting it.
KEEP UP THE GOOD WORK!

[paulc]

I use this trick mainly on my CRO, lovely trick Dave.

[GodzillaGoesGaga]

2 thoughts: #1) use math math=abs(ch.1). #2) use infinite persistence - you’ll get rid of the low frequency sweep problem.

[aaronazz]

Mind blown. Looking at my scope in a totally different way now. Thanks mate.

[brettcgb]

I really wish you had looked at one feature of the signal generator - marker frequency.

The trigger pulse indicates the beginning of a sweep with a rising edge. Normally, the falling edge is simply placed half way between rising edges. The trick here is that when the marker is enabled, the falling edge of the trigger occurs when the generator output frequency matches the marker frequency set by the user.

[HORNETMX]

Very nice!
You can select the scope to show the Y scale in log. This way is easier to analyze the graph. But yeah, the 8-bit ADC may be too low for this...
Next step, show the phase plot :D

[rlmillr]

I have used this to see the response of all of the IF/Audio stages with an RF input sweep, since it does not matter if the frequencies are different.

[michaelduddy]

Great way to save $10K if you need to design/debug some complicated filtering and see what's going on. Thanks. Brilliant ! Any insights on how to do the same for getting a phase plot (perhaps another video ?).

[attepitkanen]

Huh, clever idea. Had to try it. I don't have fancy digital signal generator, but tested by hooking two analog ones; feeding triangle wave to VCF. Works....but tedious. And frequency range is only 2MHz max. But better than nothing...