#766 Measuring Ferrite RFI Suppression

Episode 766
I measure the frequency response of various ferrites and a couple iron core toroids. The sweep on the oscilloscope is a plot of frequency vs transmission. The horizontal was 1 to 15 MHz in a linear sweep.
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[electronicengineer]

Thanks so much for performing this demonstration for us IMSAIGuy! I've installed much more ferrite beads, over the course of my professional career, than I care to recall, however in so doing, I've imagined, almost exactly, the very type of response you obtained on your scope screen during this experiment. I never thought of actually measuring the high frequency "soaking" effect like you just showed us myself... I don't know why I am lacking in imagination, but you actually do the types of experiments that I find entirely fascinating. This is one of the main draws for me, to check your great YouTube content daily. I could have done this very experiment myself decades ago, but I honestly just never had the idea to do what you just did. Being a mostly "visual learner", this is the best way for me to learn new (or in this case old) things. You honestly have a great imagination sir. Thank you again for showing this! I really love this channel. Fred

[peterklein]

There's a way to do this without a synch pulse. I triggered on channel 2 of my function generator outputting a square wave at the reciprocal of the scan frequency (example: 0.5 seconds scan, 2 Hz). The scan will appear, but will "march" across the screen. Tweak the function generator's sweep time in small fractions of a second until you slow the "march" down to a crawl. When you can see the entire sweep on the screen, press Run/Stop or Single trigger to freeze it. (FY6800 function generator, Siglent 1202X scope).
This was a very useful video, thank you! I'm really enjoying your channel!

[subramanianr]

I feel very sorry to make my comments here.
On seeing the title of the video I thought that you have read/learned something about the ferrite and the iron powder cores; because I had made some clarification when you posted a video on your attempt to make "a low pass filter" for 7 MHz using the "yellow-grey" type 33 or 08 mix iron powder cores.
I had told you that it was a low frequency mix suitable for less than 1 MHz switching power supplies. It has very high saturation point, volume resistivity and Curie temperature. It's good for using to suppress EMI on lines carrying high current DC or low frequency AC. You can find them in the SMPS of all kinds.
You answered to one of the comments that there is no standards available; not anymore.
The "Fair-rite" and the "Micrometals" of the USA are the largest manufacturers and they have the colour code standard for the iron powder cores and of course there is no way to discriminate between the ferrite mixes just by looking at them.
Again one has confusion with the "yellow-clear" (mix 6, with initial permeability of 8, a material good for narrow band, high Q inductor as in a filter from 14-70 MHz) and the one bulky (and few smaller) core "yellow-white"( mix 26, again good for the SMPS EMI suppression, ie, less than 1MHz.
The ferrite cylinders (or sleeves) are made of mix 43, 31, 33, 61, 75 or 77.
Mix #43(HF) and #61(VHF and UHF) are used to suppress RFI in the amateur radio use. They're made of Ni-Zn. Initial permeability is less than 1000, like 850 for #43 and 125 for #61.
You Ni-Mn mix with high permeability like 31, 31, 75, and 77.
Type #31 is a new Ni-Mn mix that can be used for RFI for the HF, VHF and UHF bands.
W2DU BalUn consisted of sleeving several Ni-Mn, #77 torroids over the coax cable at the feed point to avert the CMC (common mode current) that tends to flow down the cable towards the radio.
Then there are #52 and "K" materials (Ni-Zn) for the recently popular "EFHWA", end fed half wave antenna apart from the #43.
Please study about the mixes, saturation, coercivity, magnetic flux lines, volume resistivity, Curie temperature, inductive, capacitive and resistive components of the reactance in a torroid coil etc.
Every inductor (whether air cored or ferrite/iron cored) would have a reactance proportional to the frequency of the AC (RF) and it is used widely meticulously chosen for the particular application.
People think that it's a subject of conundrum but not anymore.
The "Fair-rite and the Micrometals" offer a very elaborate products catalog and datasheet that's a kind of Bible for every RF enthusiast. I think you are coming across the name Fair-rite for the first time.
The late G3TXQ, was one among many whose works should not be ignored in the addictive hobby of "HAM RADIO"
Good luck to you.
I have been a fan of your channel for more than 2years since you started making videos on the "Nano VNA". I suggest you make great videos with correct scientific content.
De VU2RZA

[gsansoucie]

Glad this video popped up, I have a box of those cheap no name snap on ferrite beads that haven’t appeared to have any affect on my rig. Now I know why. I have an O-Scope and a signal generator, but no means to inject a sweep. But you gave me an idea to use my Oscope to test my wires for suppression. Thanks.

[bobkozlarekwasqq]

If you increase your test frequencies I think you’ll see they are much more effective. Most of the snap on tape chokes where designed to minimize higher frequency noise such as that for me switching power supply. For lower frequency work I’d start out using cores that are made from a mix 75 material. I have found that multiple turns of wire through one individual core tightly wound works much better than slipping multiple cores over one wire. Regarding the yellow core it’s very large for the skinny wire that you’re passing through it you need much tighter coupling between the wire and the inductor

[briandonaldsonstringgui]

I know, 2 years later, but gee I wish you had a cleaner desk so we could see how you connected your test leads. But it did give me an idea on how to use my NanoVNA and TinySA with my Oscope to test some snap on beads. Thanks

[zeno]

You showed that the straight wire on its own made a difference (because it had some inductance) but what would have been interesting would have been to compare a ferrite core that you wound a couple of turns through with just the turns without the core. This would have shown what the core added to the inductance of the air-cored coil.

[krmj]

Another great video. Thanks for all your efforts. I'm going to try that with my VNA

[samuellourenco]

Some of the rings are ferrite, while others are made of sintered iron powder. They have completely different characteristics and applications.

[Greg_Chase]

Ferrite has a skinny ('narrow') hysteresis curve, which in laymans terms, means that a AC/RF alternating signal can more easily flip the electron spins (the magnetic field) in the material, compared to iron. Ferrite is made partly with iron but mixed with other elements.

The benefit of the ease of flipping electron spins (aka reversing the magnetic field in the material as forced to do so by the alternating current, the AC or RF) - is that less energy is spent torquing the electron spins in a new direction during the flip in each of the two half-cycles in each period of the supplied frequency.

So ferrite is used in transformer cores because (1) it still increases the magnetic field compared to free space, since it contains iron, but (2) without the loss of energy of a 'thick' hysteresis curve like iron has. RF chokes benefit from the same "let's not waste too much power torquing these electron spins back and forth" motive.

The technical term for 'running roughshod' over electron spins in this regard is coercivity. "Low" coercivity means the electron spins (the magnetic field) are like the subjugated minions of a powerful totalitarian dictator: "do it now, with no resistance!" type of deal.
.

[WBIN]

He doesn't say if the input of the 'scope is terminated or not. (like transmissions lines are) Ferrite cores absorbs the energy and add inductance and the iron cores mostly add inductive, that is why ferrites are not painted. I think sweeping to 30 MHz would have been appropriate. (HF bands) Ferrite beads are called "VHF beads, " they prevent VHF oscillations in some circuits. (usually in high impedance inputs) Ron W4BIN

[jdmccorful]

As is in everything else. Thanks for the look.

[dapperdave]

I've been going to Amidon Corp for my ferrite needs for many years. Great resource to determine which mix will work best for the results your looking for...Mix 43 is my fav. ExtraOld Ham with a GROL/w Radar here. Enjoy your videos very much OM

[glasslinger]

Impedance matters. The impedance you are feeding with the choke will have quite an effect on the attenuation. The reactance of a clip lead is quite high which may be the reason for the poor attenuation. Try a .001 mf capacitor on the output side.

[perryjones]

A lot of ferrites are aimed at radiated emission from leads, that is to say, above 30MHz where they become lossy (by design) turning emi in to heat. They often hit their sweet spot around 100MHz, so with these, might not be much attenuation at all 15MHz and below.

[jameswest]

More turns more affective as you probably already know

[TheRetiredtech]

Wonder if the Nano VNA could do this.i loved the demo.

[eddydogleg]

LOL black arts. What learn from working w/ geologist is that geology is a black art. It drove me nuts when they'd ask me to change vertical depth of the well a quarter metre. Always fun to ask them which side of the 158.8mm bit they want on that 250mm change in vertical depth.

[Bobo-oxfj]

That "Absolutely!" is the benefit of dealing mostly with technically inclined people, you don't typically need to walk them through a flowchart to make sure the product is actually turned on before sending out new parts...

[johnwest]

If I recall correctly, the Yellow/White are not ferrite, but iron powder, a 'mix 6', and you are basically correct about what they are good for and what ferrites are good for and why. And certain core types are good at certain frequencies for noise suppression and good at other frequencies for wide-band transformers. Or are you looking for a high Q coupling transformer for a particular frequency? In fact, most core materials aren't good for 'a frequency' per se, but good at various different things at various frequencies. So you need to know your application for different materials. The ham's friend, ferrite mix 43 is actually pretty poor at handling high power. That's why hams running a KW and a half use huge ones for their antennas. They can be easily and permanently cooked. Powdered iron typically can't be permanently cooked and thus is better for high power.

And of course different manufacturers have their own ways of describing the characteristics of their products. Nothing is standardized. I've been reading about this stuff for the last month and I'm only now figuring out what to use in what size for what application. Even then, I still don't know if what I've selected is the very best choice for the application, or just 'good enough'.