"25KHz is quite high frequency"... Tell that to The Signal Path lol

Somewhat related - railways that use "axle counter" train detection systems often make use of a form of magnetic sensing where a tx and rx coil are placed on either side of a rail and nominally there is a certain minimum magnetic flux linking the two coils. When a train wheel passes over the rail (directly between the rx and tx coils), due to the wheel being of a high permeability material (steel) the flux is rerouted through the wheel structure and the field at the rx coil is much lower - hence a train wheel has passed. This saves on older mechanical parts that physcially switch as a train passes as these fail more often + it's a right side fail safe system as if the tx coil loses power, the field will diminish at the rx coil and will seem as though a train is there rather than failing to detect any trains passing.

I've seen this before. I was a service engineer for an electron microscope company. I had a customer who had to spend $200k USD on room prep because they decided to put a TEM and SEM next to where the 13KV building supply came in. Just what you want next to sensitive equipment. With fully welded walls of thick Al and vibration mitigation, the room was AMAZING. Except for low frequency magnetic field fluctuations. I could tell in the image when the elevator half way across the building away moved.

You need one 'o them there "cow shields" made of "moo metal.

Thanks for another informative video Dave. I love the way you can make "dry" sound like a "fun adventure".

This is fascinating. Thank you.

That's videos I expect from you .... great! Short, explanatory and so useful.

Love the excellent visual explanation, nothing makes a better experiment than seeing the measurements take place on the instrument in near real time

Another technique that's useful for very low frequency/DC magnetic fields is active magnetic shielding via Helmholtz coils. Completely impractical for compact applications but does create a controlled environment when testing out sensitive things like magnetometers.

Your videos are always very interesting. Thumbs up!

Really good demonstration about the importance of the proper shielding!

Thanks! I learn lots with your videos! 😊

So I better swap my tin foil hat for a copper hat to stop the government from mind reading 🤣😂😆😉👍

Very informative video. Thanks!

The all new Trojan copper shield, reduces probe sensitivity

*Dave:* 25kh is quite high frequency *Shahriar has left the chat*

Though the CRT is shielded on the sides, the front is glass with a mask. The H field can easily be transmitted through the front of the CRT. At the very end of the video you held the aluminum box higher and the effect was much lower. Putting the Al, Cu & steel sheets in between completely covered the glass front of the CRT that was not shielded.

great vid - I have one of those DSA's and I ended up making a simple remote control for it so I could start the averaging (plus a couple of other things) as I moved things away from it

Thanks, learned something more.

I am a audio tech, got a desperate call at 5AM there was noise everywhere in the mixing console. I tried to talk through it but was forced to go in at 5am. The Studer 24 track machine has Mumetal shields on the head guard. There was an CRT computer monitor sitting on the meter bridge a couple feed from the machine. The assistant had forgotten to flip up the head shield when loading the tape. I was not happy and knew what the noise was as soon as I saw the test box sitting in front of the CRT in this video.

The basic thing you need for H-field shielding is a good magnetic conductor. Mu-metal is one example.

What about mu-metal shielding? I mean actually testing it. But yeah this was actually what I was yelling at my screen with last video. Again a nice video Dave. You're on a roll lately 👍🏻👍🏻

I guessed "too close to the monitor" last time. Yay

Love how it's 2020 and we have a black and white printout of a youtube video haha

I hear all of the “preppers” saying that to save your electronics, during a solar storm or a nuclear blast, that a microwave oven is shielded enough to stop the EMP. Could you make a video explaining if this actually works or not?

oh man, why don't you say this earlier ... i got such problems :-D thx great info

Great vid! It seems to be more spatially related to the 3.5” disc drive, right?

Good deal. Reminds me I can still move forward on the spiral conical antenna instructable since I left off with only the "form." Excellent referenced video for sure. Makes me wondering what newer high magnetic permeability materials can do, to improve performance of the older systems. en.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials Same thinking goes with...., I think it's the OLED's are the quietest... though, mainly thinking upgrading the sources of noise, RFI, EMI, etc. in the systems for a modern upgrade to the old boys. Would be nice if silver foil was more commonly available. I guess that's what's used to line the mil/intel grade boxes. Plasmonic resonance frequency is one of those newer buzz words to me... though is more to do with electric effects and I guess somehow with magnetic... though the magnetic world is another beast. Just like polarization. Tables with polarization related to electric characteristics don't seem so common... same with the magnetic characteristics. Great demo! Thanks for sharing! Good fun.

Any ideas for a probe to sniff around an enclosure for EMF? ie efficacy of screening / protection.

Do you have any nickel silver (also sometimes called German silver) to try it with? Most of the shielded enclosures I've seen in devices use nickel silver.

Would have loved to see a CRT next to a LCD both doing the same measurements

I often found 15.625 Khz in many older classical music. disc albums on sale, they came from CRT TV and can be annoying to listen.

You could also try sintered ferrite sheets such as Würth FSFS 357003 or Kemet EFX

Fun and Interesting

Interresting...

Early PC stuff--put the CRT monitor on top of the floppy drives creates interesting effects. The drive head amps get the EM field from the CRT deflection circuits and the video goes wobbly from the magnetic field in the drive spindle motor. Add a steel hood over the drives and you can read and write disks, but the display still goes a little wobbly from the very low frequency of the motor magnetics.

Hm. Bet you could do a whole video or a whole series of videos on shielding. You could even try to answer the age-old questions: Do I ground my shielded cable's shield at one end or both? If at one end, which end?

i have heard that for low frequencies, mains frequency, one can use Laminated Copper around 6" thick or more for shielding. Based on this video, I wonder if laminated mild steel would be more effective. This is how one would shield their homes from power distribution lines near their homes. Of course, if one is planning on trying this, you will need to dramatically increase your foundation footing and foundation. Same for roof rafters. Same for walls.

The wonders of Black Magic and RF at a cool 25kHz - neat.

At my job I have to do testing for ingress into a coaxial cable network. Sometimes it doesn't matter if the meter is connected to anything or not it will fail in certain areas of town. Bad shielding on the meter. If I put the meter inside my vehicle's steel center console, I can get my test to "pass".

For a free high permeability steel for making your own near-field magnetic shield, breaking open a discarded microwave oven, the big transformer inside contans laminations of silicon-steel which are high permeability. An edge grinder can easily remove the two strip welds that hold it together, and the laminations are relatively thin sheets that are also relatively soft and can be cut with sheet metal snippers and then hammered flat on an anvil. If you recycled and put a big transformer into one of your projects, it might benefit from this kind of shielding from the near-field magnetic radiation. HTH.

quite interesting Dave has the added problem of needing to get his test equipment and the device he's testing in the same shot. Most people would have the analyzer about an arm's length away.

Can anyone tell me if the sheild needs to be grounded or isoilated and what would the affects be in either case?

Why don't you use [Pause] button on your analyzer when you want to show averaging results for a period of time when display was closed?

The skin-depth for aluminium at 25kHz is 0.5mm. If you take a thicker material (and not a zinc alloy but conductive aluminium) then a 3mm sheet shall block M-fields almost completely. Warning - a "cut-line" - i.e. where the lid closes on the box - compromises the integrity of the shield. (this is why the copper "strip board" perf-board does not shield at all at 8:19 ). Most magnetic shielding can be done without mu-metal, just with good design and some thought. Mu-metal or other high-permeability ferromagnetic metals have potential to fail too, if slapped-on without careful thought.

Skin depth of Cu at 25kHz is 400um+, and 1oz is around 35um so you wouldn't expect much effect from such a thin layer.

Of course the simplest & easiest solution is to not put your super-sensitive instrument next to a bloody CRT. ;)

Watching a video of a printed screenshot of a filmed piece of paper. Inception!

Isn't that pink bubble wrap mildly conductive? I.e. anti-static? Is it OK to wrap a bare circuit board with it?

Will Copper coloured paint help?, Asking for a friend. Great demonstration of our 'Noisy surroundings'. Thanks for sharing.

Where can I buy this device?

9:15 nice. You've invented a movement sensor based on EMI 😅

Many guitarists use coper tape inside the guitars 1/4" output jack partition, the jack socket is mounted to a plate that lifts off,and a small compartment is behind. The jacks sockets are very usually unbalanced so they try to quieten the noise with copper. So should they be using a mix of metals to prevent noise and many layers of metal tape? 1khz and below is very important.

Dave, what effect does gamma radiation have on a capacitors dielectric?

what about a faraday cage?

Although it's not relevant to this 25KHz testing, you said "If" there were low frequency fields of around 100Hz present. Surely there actually was, due to the vertical deflection coils of the CRT?

Hello this is Thomas does anyone talk about HP power source

So 25kHz is the frequency the CRTs magnetic field is operating at, what's happening at 50 and 75? Harmonics?

So that means that those old game consoles that had big copper sheets in them (e.g. the Sega CDX) were for protecting the electronics from CRTs! I’ve always wondered why they looked engineered to withstand the apocalypse.

Dave, you are the nearest electronic Genius I know. I'm seeking an answer or the path to find the answer to this question: "Is there a frequency range, through which an internet type packet communication could be passed through the power grid? " Even pulse DC? Thinking there might be a way to utilize the power grid to communicate information long distances to the boonies where there are few other communication methods. Any thoughts where I could beneficially pursue a meaningful answer. Thanks Dave.

Thought you had ground beef in there by the thumbnail

Quick test to know if a metal has high permeability is to see if a magnet sticks to it. Sticks = high permeability

What if the shields in this video were grounded? Would that help at all?

is this the basic of faraday cage? can you do a video on faraday cage?

Dude, it’s the pink bubble wrap !

can you teardown ram or storage of smartphone ?

Why EMF in Low Field is higher than in Low field

I hope to understand your words in the Arabic language Honestly, I hope the translation system gets excited and learns from you. I cannot express my gratitude to you

If you connect Ch1 to the Source output on the 35660 you will probably see the same. You probably have to zoom in at 24.665 kHz with 1 kHz span. The shielding between the CRT and the signal generator is not that great in this instrument.

Was that a tenacious d reference there? Dave? Are you also a man of culture?

Need some transparent aluminum?

For magnets you want bismuth shielding.

Something I've noticed...... Most people pronounce the letter H as "aych"......... and some pronounce it "haych". Dave is the latter.

What would have happened if you would put a copper enclosure inside an ferromagnetic enclosure? Edit: I should have waited till the end before posting a comment.

A steel/iron sheet ideally mu metal as you mention while I write this comment will be best

I thought it was raw meat in the box from the thumbnail 🥫

WHY are you using an antique 30+ year old CRT signal analyzer, when you have modern LCD wide-bandwidth spectrum analyzer ?

From the preview I thought you had a steak in there

You HAVE to do a deep dive on the new ATX 12vo PSU standard it's a fucking dumpster fire in my opinion.

FYI, KZfaq suspended sending email notifications to all subscribers.

Hm, how about that. I always thought shielding didn't work unless it was grounded...

Try using screws on the lid and shield the gap between the lid and the case.

"hach"

I never get why aluminium foil is so effective at shielding RFID, since RFID is basically only the magnetic field.

I need a analog used but working oscilloscope . I am a poor guy I couldn't afford even 50 dollars .So can you please send me some link of oscilloscope which is under 20 dollars including shipping because I am in India

OK i don't mean to be that guy, but when I post this there is 1 thumbs down. I must know what is wrong with this video? i mean its in focus, informative, has audio, to the point, has some experiments... What is wrong with this video that it deserves a thumbs down?

"This is just a tribute" - Did you just made a Tenacious D reference?

MVVblog is better