Understanding EMI Debugging with Oscilloscopes

[@deemaaameen4722]

you are great Paul, very nice explanation

[@shazam6274]

Very good explanations: straight forward, succinct yet full of detail. Unfortunately the Title is misleading having the word "Oscilloscope" in it. The "'scope" is being used as a Spectrum Analyzer, and the majority of oscilloscopes don't have that function! The main difference between using a 'scope and an SA is that the 'scope has a high impedance input stage, suitable for these kind of probes and SAs have a 50 Ohm input impedance which would greatly reduce the signal amplitude from these probes to almost useless values. This of course can be negated by adding an LNA between the probe and the SA, but that will still load the probe and add noise.

[@pauldenisowski]

Thanks for the feedback! I have a second video "Understanding Near Field Probes" that addresses the issue of signal amplitude and the need for a preamplifier when using an oscilloscope for EMI debugging. I would however beg to differ that the title is misleading: the vast majority of EMI debugging is in fact performed using oscilloscopes, not spectrum analyzers. You're absolutely correct that effective EMI debugging using a scope requires that scope to be able to display frequency domain information (using an FFT) similar to the way a spectrum analyzer works. One can also use a spectrum analyzer in zero span mode to display time domain information (voltage or power as a function of time) similar to the way an oscilloscope works, but that doesn't make a spec an into a scope, even if some manufacturers might refer to zero span as "scope" mode :) Historically, "hobbyist" level oscilloscopes have not had an FFT/spectrum analysis function, but this feature is more or less standard on even entry-level "professional" oscilloscopes. My feeling is that FFT/spectrum analysis will soon become a "standard" feature on many hobbyist oscilloscopes as well. Thanks again for the feedback!

[@shazam6274]

@@pauldenisowski While there are significant differences between the FFT functions of Oscilloscopes and Spectrum Analyzers, the functionality and use demonstrated in this video is that of an SA, not an Oscilloscope! If by "hobbyist" oscilloscopes you mean ones which cost less than a new car, you could be right. But most professional engineers in the world use oscilloscopes which have either no, or unusable FFT functions in their daily work. There is one R&S competitors who makes a 'Scope and real SA in one instrument (at the price of a modest car). Ask the R&S marketing department, they are likely to have the data. I have , along with many others, used both 'Scopes, and SAs to hunt down EMI sources (including 20mm long PCB traces) on PCBs and scopes are much faster than using the slow SAs In either case the 'scope has to have a high bandwidth to be effective (i.e. >300 MHz). Those nearfield probes are a waste of money. They were developed to find RF leakage of large equipment racks and big box chassis, not at small, PCB areas. Get a small wire wound inductor (or wind one on a tooth pick) to pinpoint problematic traces and components. This will also require a small inexpensive 20~30 dB LNA.

[@nomadic_rider42]

Very useful information, thank you.

[@smollande]

Thìs was very helpful. Im looking for a way to detect extremely low frequency emi and it seems that oscilloscopes are the way to go. Quick question - is there a near field probe for radio frequency interference (mW/m²) that i can use with an oscioscope with fft?

[@JohnHarnishBLACKBERRY]

Very good

[@johnf4085]

Thanks

[@JohnHarnishBLACKBERRY]

Very good

[@JohnHarnishBLACKBERRY]

Very good

[@pauldenisowski]

Thank you!