Oscilloscopes, Microphones, and Noise - ECE Topics #5

How to use a high-resolution (12 bit) oscilloscope to look at microphone signals directly - without preamps / etc. In this video, we look in detail at the noise that typically makes direct measurement of microphone-level signals (e.g. 3 mV) impossible. The noise is traced to radio frequency interference (RFI) from switch mode power supplies (SMPS) and strong radio signals in the area. We show how to easily fix the problem.

[@fjs1111]

Your videos are absolutely the best anywhere for RF stuff!! thanks

[@MegawattKS]

Thank you ! I was happy how this one turned out and amazed at how well simple passive filtering did the job :-)

[@W1RMD]

Thanks for this valuable information. Take care.

[@brianbirkinbine2054]

Great idea, will have to try it out, recently was troubleshooting audio on my daughters headphones using my Rigol dho924s and want to see the results with this filter installed.

[@edisukriansyah5230]

Very helpul sir. All of you video is the best

[@MegawattKS]

Thanks. Very much appreciated.

[@mudspringer]

Excellent!

[@mikesradiorepair]

Check your comments section "held for review". I posted a reply with links to a high quality commercial 20kHz LPF made by ThorLabs. Looks like the comment got blocked because I added links.

[@MegawattKS]

Thanks! I checked, but it's now showing me the comment either. So I went to ThorLabs and found this one (let's see if it lets me include the link). They're a bit pricey - but look nicely made. I was a bit confused about their spec of using them with 50 Ohm source and high-Z load. Presumably they might work with a 1X probe, but not sure. If it is an LC ladder filter with a capacitive input section, 10X could be problematic. Maybe that's why it's spec'ed under conditions of a 50 Ohm source... Have you used them with a probe? www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=8613

[@mikesradiorepair]

@@MegawattKS LOL, I went back and watched the video and it must have gone in one ear and out the other when you mentioned you had looked at the ThorLabs filter. When I'm using them I'm connecting them to a 50 Ohm system so didn't even think about the input impedance. In your application you probably want a Hi-Z input so you don't load down the circuit. What you made is probably the best option. I don't think companies make them because most people just make one like you did or have instruments that already have them built in. My R&S audio analyzer, R&S communications test set and even my old Sencore Stereo PA analyzer all have selectable audio filters built in.

[@weinihao3632]

Oooooooooooooooooooo

[@MegawattKS]

:-)

[@You_T_Channel]

You sound like the actor Billy Bob Thornton

[@MegawattKS]

Interesting. I'll have to listen to him :-)