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The Proper Split Beads to Suppress RFI:

from Alan Applegate, KØBG on February 25, 2004
View comments about this article!

The Proper Split Beads to Suppress RFI:

Ferrites are mixtures of iron oxide and one or more metals typically manganese, nickel, and zinc. Occasionally rare earths such as yttrium and scandium are also added . They provide high magnetic permeability and high resistivity, although some formulations (known as mixes) are conductive. Combined with a variety of stabilizers and binders they can be molded to just about any desired shape, with toroids, bars and beads the most common ones encountered by amateurs. By selecting the right mixture of metals, initial permeabilities from 10 to as high as 5000 or more are easily obtained. To a lessor extend the temperature coefficient can also be adjusted to meet a specific use. There are literally thousands of uses for ferrites and a modern amateur transceiver is loaded with them. But it isn’t their use as RF transformers or baluns or ununs were concerned with in this article, but their use as RFI suppressors, and primarily in split bead configuration.

Split beads are tubular chunks of ferrite split along their length and typically mounted in a reclosable plastic enclosure. They’re available in a variety of mixes, inside and outside diameters, and with or without enclosures. -- Since our focus here is high frequency RFI suppression, we’ll concern ourselves with just one mix; 43.

A mix 43 split bead has an initial permeability (expressed a ui) of 850 and a nominal operating range of .01 to 1 Mhz. When placed over a wire where there is RF energy flowing (between one and several hundred megahertz) it is equivalent to placing an inductor and resistor in series with the wire for RF currents. Depending on the frequency of the RF energy the equivalent impedance can be as high as 50 ohms yet DC or audio frequencies pass through unrestricted . It is this property, which makes their use in RFI suppression so ideal, and the best part is you don’t have to cut the wire!

The basic application I just described, a one turn inductor, will suffice is some cases. However in more stubborn cases or where more RFI suppression is required, additional beads can be installed. This is particularly true with tank-mounted electric fuel pumps. As an alternative, if there is enough lead length, multiple turns can be used .

I have used 28 ferrite split beads to RFI suppress my Acura coupe. They’re installed on the Navigation computer, AC and cooling fans, AM/FM radio leads, COP (coil over plug) control wires, four rather large ones over the fuel injector wiring harness, and four smaller ones on the fuelpump harness. In addition there are several snapped on to my Icom’s remote mounting cable and the wiring to my homebrew remote control for SG235 and SG500 mounted in the trunk. It is these latter two uses where I discovered an important fact; not all split beads are created equal.

Good, high quality split beads are not inexpensive. At upwards of $5 each, multiplied by 20 or more, and it can easily run into a healthy sum. This fact has pushed many amateurs (me included) to seek relief by purchasing surplus units from after-market sources. The problem is, you don’t know what you’re getting. Some of these surplus split beads are mix 67 (ui=40), which is virtually worthless for HF RFI suppression. Sometimes you might find a bargain if you had a way to check the mix. This takes some rather expensive equipment and since initial permeability can vary as much as 20% between batches of the same mix, you can’t be 100% sure even then. What’s a poor ham going to do? Relax; cause here’s a way to get close.

Nowadays, the MFJ 259B Antenna Analyzer has become almost ubiquitous in the modern ham shack. And believe it or not, you can use one to check those surplus units to make sure they’ll do the job. You’ll need enough hookup wire, size 22 is ideal, to make 5 passes through the bead plus enough to connect the ends to the analyzer. Set the frequency to 2 Mhz, and measure the reactance. If it is mix 43, the inductive value will be approximately 500 ohms. Pushing the mode button three times will bring up the reactance menu which should show 40 uh or so. Any less than this and you may not have mix 43, and it may not work properly. If the reading is higher, that’s fine to a point, but double these figures may indicate mix 77 (ui=1800), which is better suited for 160-meter suppression. By the way, the 259B hasn’t enough range to check mix 43 at much more than 2.5 Mhz unless you reduce the number of turns .

I wish to thank Tom Rauch, W8JI, for his technical expertise in preparing this article.

Happy Suppressing!

Alan Applegate, KØBG

Notes:

They are not always (or predominately) iron oxide, and may contain “soft iron” meaning magnetically soft not physically soft.

Size (length) does matter. The resistance to the flow of RF current is closely tied to the linear inch of material parallel to and surrounding the wire, and it goes up by the square of the number of turns. It is actually a complex impedance, with X decreasing and R increasing with increasing frequency. At some frequency X=R (loss tangent equals effective permeability) and the Q becomes unity (Q=1).

It is always preferable to use multiple turns as the impedance increases with the square of the number of turns.

The 259B has a maximum reactive range of 650 ohms. A mix 43 (ui=850) bead with 5 turns will exceed this value at approximately 2.5 Mhz.

As pointed out in a previous footnote, at some frequency X=R and the Q=1. For mix 43 (ui=850) this occurs at or near 38 Mhz for a one turn core, and approximately 15.5 Mhz for a two turn core. Attempting to measure the crossover (X=R) point with a 5-turn core is beyond the range capability of the 259B. For those who wish to get closer to the actual mix specifications, loss tangent charts are available from a variety of sources which precisely list these crossover (X=R) points.

Member Comments:
This article has expired. No more comments may be added.
 
The Proper Split Beads to Suppress RFI:  
by W5ONV on February 25, 2004 Mail this to a friend!
Alan,
Just wanted to thank you and Tom for the info posted here.Very well written and good explanations. I do understand ferrites better now. 73 Jim
 
The Proper Split Beads to Suppress RFI:  
by WA4ET on February 25, 2004 Mail this to a friend!
Well after reading your short artical, I feel alittle better informed on the subject. Since I have been chasing RFI in my Jeep Grand Cherokee for several weeks, it is also timely.

I purchased a bag full of split beeds,, and what I mean is a bunch of differant size spilt bead chokes that has turn into a bag full to place at strategic locations to eliminate many of the things you related to in your own quest to quite your vehical down. UNfortunatly I have no idea of the mix number, as very few places I have found even stock them, say anything about them other than lenght and ID/OD measurements

You might say where you purchased your split beads, as this would be very usefull to those that read your artical. I was able to find a nice selection of SPLIT BEADS and TOROIDS at a place called: WWW.Allelectronics.com. THey have a nice web site and seemed to have there act togather. Fast shipping, and the email you all the tracking information without haveing beg for it.

DAvid

 
The Proper Split Beads to Suppress RFI:  
by KG4GSC on February 25, 2004 Mail this to a friend!
Excellent material....printed out and added to my tech reference in the shack! Heh...and I was just eyeing that stack of ferrites sitting in the junque box.....

Thanks again;
Andrew
KG4GSC/AG
 
The Proper Split Beads to Suppress RFI:  
by W2NSF on February 25, 2004 Mail this to a friend!
Great advice.
I've just found out that our front-loading washing machine is responsible for broadband interference to my HF station. It was an education for me to observe all the combinations of speeds and direction-changes that these front-loaders go through during a cycle. They use an electronic control system on the motor that spins the drum - and that's the source of my RFI. I intend to put some split ferrite beads on the power cord of this machine; I will report back on my success. Now, I'm going to check out the rest of our home appliances to see if they're similarly controlled. The blower in my heating system comes to mind...
 
The Proper Split Beads to Suppress RFI:  
by K2VJK on February 25, 2004 Mail this to a friend!

Great article. Will become a part of the references in my shack. Thanks.
 
RE: The Proper Split Beads to Suppress RFI:  
by K0BG on February 25, 2004 Mail this to a friend!
Palomar Engineers in Escondido, CA and Surplus Sales of Nebraska both sell split beads with the requisite snap-on plastic covers. Both of these companies list the mix in their advertizing. Where ever you go to buy them, if the mix isn't listed, go someplace else.

Alan, KØBG
 
The Proper Split Beads to Suppress RFI:  
by K9FTB on February 25, 2004 Mail this to a friend!
Alan & Tom,
Thanks for making this info available in "readable" terms! I just checked All Electronics website and found about 15 split bead ferrites available. Unfortunately there was no "mix" information posted for any of the ferrites. The only info available on the site was the physical size.

This seems to be common among internet providers. So where do you go to get the details you need to purchase the "correct" split bead ferrite to have a positive effect on an RFI problem?

Excellent article - keep 'em coming!
 
The Proper Split Beads to Suppress RFI:  
by W4VR on February 25, 2004 Mail this to a friend!
It's about time someone posting a constructive article for a change, instead of the constant CW and ARRL bashing that takes place on this web site. Thanks for the tip on measuring the reactance of these beads. The Autek RF-1 may also be a useful instrument for making bead inductance measurements if you don't have an MFJ bridge.
 
RE: The Proper Split Beads to Suppress RFI:  
by KG6AMW on February 25, 2004 Mail this to a friend!
Good article Alan. I’ve read ferrite material 73 (now referred to as mix 77) was always quite good to use. This is due to fact that it provided good RF attenuation from 1Mhz through 50 MHz with peak impedance about 25 to 30 ohms at about 25 MHz which covers the HF ham bands nicely. Material 43 on the other hand covered the medium frequencies with optimum frequency attenuation from to 40 MHz to 400 MHz. However, material 43 has extended impedance (less than material 77) down to about 10 MHz at about 15 ohms versus 26 ohms for material 77. wouldn’t material 77 be more effective for controlling RFI? Thanks.
 
RE: The Proper Split Beads to Suppress RFI:  
by NI0C on February 25, 2004 Mail this to a friend!
Thanks Alan and Tom for this useful information. I operated from an apartment for about eight years, where my antenna was only a few feet away from my station. The receiver picked up a lot of noise from the Commodore 64 computer I used for RTTY. I got rid of most of the noise by using lots (dozens) of ferrite beads. I remember going to several Radio Shack stores and purchasing all the beads they had.

I would only add that split beads need to have extremely smooth mating surfaces so as to avoid introducing an air gap in the magnetic path. Any hint of an air gap would greatly diminish the effectiveness of the bead.

Alan, how's your gas mileage in the Acura now that you've added all that extra weight to your car?

73 de Chuck NI0C
 
The Proper Split Beads to Suppress RFI:  
by W8AD on February 25, 2004 Mail this to a friend!
Hi Alan,

Nice job and very useful! This is the kind of stuff that SHOULD be on e-ham articles instead of all that inane self-centered flaming about code, band segments, dumbing down, licensing and the "sky is falling", etc. Don't misunderstand, there are important issues but they never get solved by flaming, but by properly communicated rational approaches.

I think the flaming from all the old walruses has driven away more new or potential hams than any one other factor (I'm an old walrus too, but I try not to flame!).

Now, articles like this this one will ATTRACT more hams to be active even when they have RFI problems, because it answers questions and provides solutions. Great job---let's have more of this kind of stuff.

Don, W8AD
 
RE: The Proper Split Beads to Suppress RFI:  
by K5UJ on February 25, 2004 Mail this to a friend!
I was under the same impression as KG6AMW, that 77 is better for trapping HF RF, and that 43 is better for VHF. I made a bead 1:1 balun with what I suspect are 43s from RF Parts. Since 43 will work on HF (you just need more of them to get the same result to be had with 77s) I calculated how many more I needed from data at the Amidon website and used them. No problems so far.

Rob Atkinson
K5UJ
 
Permeability: For DC, isn't higher always better?  
by KF6IIU on February 25, 2004 Mail this to a friend!
>> mix 77 (ui=1800) ... better suited for 160-meter suppression...

Why isn't the rule, "the higher the better", as far as permeability is concerned? For most applications, I am putting the choke on a DC lead to suppress common-mode interference up to as high a frequency as possible. So for DC applications I would want as much permeability and thus inductance as possible, right?

I suppose we want to carefully consider the permeability of a random bag of beads we buy because it is more likely that they are some material that is too low to be useful, rather than too high.
 
The Proper Split Beads to Suppress RFI:  
by WD4HXG on February 25, 2004 Mail this to a friend!
For those wishing to continue work with ferrites the following link provides Fair-Rite's notes on
working with ferrites from low hf to vhf.

http://www.fair-rite.com/CUP%20Paper.pdf

The paper is about 9 pages long and although not difficult reading, there is a lot of info to correlate.

Thanks Alan for writing on your findings and starting this thread.

 
RE: The Proper Split Beads to Suppress RFI:  
by KC8VWM on February 25, 2004 Mail this to a friend!

>>>>I've just found out that our front-loading washing machine is responsible for broadband interference to my HF station.<<<<

Are you getting 2 cycle or 3 cycle noise? It must have you in a real spin...


 
The Proper Split Beads to Suppress RFI:  
by W4VR on February 25, 2004 Mail this to a friend!
The only way I was able to stop my garage doors from opening when I operate 160 meters was to install a 2.4 inch donut made of 73 (or was it 77) material in the ac cord of each garage door opener. In fact I've been using beads of 73 material for most of my RFI problems and this material has worked better for me than the 43 type.
 
The Proper Split Beads to Suppress RFI:  
by KG4OKV on February 25, 2004 Mail this to a friend!
Amidon, manufacturer of ferrite an iron beads, bars, torroids, has a great chart giving tons of good info on this topic. If you contact them I'm sure they will be happy to send you one.
Bill
KG4OKV
 
RE: The Proper Split Beads to Suppress RFI:  
by KA4KOE on February 25, 2004 Mail this to a friend!
I wonder how well these would keep RF out of shack when put around the coax feeding, you guessed it..

A FAN DIPOLE
 
RE: The Proper Split Beads to Suppress RFI:  
by K1OU on February 26, 2004 Mail this to a friend!
Does anybody know if W9WHE is still boycotting the ARRL?
 
RE: The Proper Split Beads to Suppress RFI:  
by N6AJR on February 26, 2004 Mail this to a friend!
you put the beads on the coax going to the fan dipole to pull rf off the shield (or use a 10 coil coax balun at 6 to 8 inches in diameter..) does the same thing yea fan dipole.. tom N6AJR :)
 
RE: The Proper Split Beads to Suppress RFI:  
by W5ONV on February 26, 2004 Mail this to a friend!
I have several ferrite beads that I pulled out of some old UPS units. They are 1.5in by 3/4in. They came off the battery side and the AC side of the units.Anyone know what type these my be ? I do not have an MFJ Analizer to check them with. 73,Jim
 
RE: The Proper Split Beads to Suppress RFI:  
by IV3SBE on February 26, 2004 Mail this to a friend!
I built a vertical Multiband no trap Antenna 30 ft high with a UN-UN at its feedpoint using an Amidon T200.
Works wonderfully in all bands except in 80M due to stray RF going back to the radio making impossible to tune with the internal ATU.

SOLUTION:
fitted N.2 Split Beads ( supplied by Kenwood ) just right at the Radio connector, magically I could tune anywhere.

Alternatively you can wound 5-7 turns of RG 58 over a T200 Amidon Toroid and fit it between the radio and the Coax to your aerial system, works magic and keeps RF out of your PC so you can operate Digital modes without that Flares that you usually see on the Waterfall on unoptimized setup.

" have a radiation free day, won't you? "

IV3SBE rock bottom budget Ham operator.
 
The Proper Split Beads to Suppress RFI:  
by K1CJS on February 26, 2004 Mail this to a friend!
Thanks for a great article! Its refreshing to see an article that has technical merit once in a while. This one has found its way to the reference binder in my shack. Thanks again.
 
The Proper Split Beads to Suppress RFI:  
by KA7GKN on February 26, 2004 Mail this to a friend!
Very nice article. Here's my two cents worth:
Go check out The Radio works MIX-31 ferrite split bead!
YES...MIX-31!!!!
It's made by Fair-rite and is machined beautifully.
They come in two sizes 1/4" and 1/2" diameters.
The price is amazing 2 bucks for the 1/4" and $2.50 for the larger one.
See the specs in The Radio Works catalog. for more techy details of the mix-31 go to the website of fair-rite.

I am very impressed with the mix-31 split bead.
just remember ferrite split beads will only reduce/eliminate common mode rfi issues not differential mode type issues.

finally don't think one split bead will eliminate the problem, sometimes it requires more. If you find yourself though, adding more than say 6 split beads on a single cable I say you have a problem with something else and you need to find the source generating the rfi

Look at the T-4 isolators at thr Radio Works if you do indeedhave a RFI problem in your shack.

[I do not work for The Radio works, they just have good stuff!]

marty ka7gkn

 
RE: The Proper Split Beads to Suppress RFI:  
by K0BG on February 26, 2004 Mail this to a friend!
Don, K8AD, thanks for the kudos.

Chuck, NIØC, I get about 19 in town, but if I use the amp it goes down to about 18. It's a small price to pay. As for the weight, it's only a few pounds!

Mix 77 is a better choice for 160 and perhaps 80 meters in some cases. Mix 43 is good through 2 meters, but there are better choices. Amidon and Ferrites.com both have charts available showing the impedances of the various mixes over a wide range of frequencies.

Palomar Engineers has a brochure which Jack will mail you on request which has some additional information on which mix to use for which RFI application.

But for HF (80 through 10) Mix 43 is the best choice.

Alan, KØBG
 
RE: The Proper Split Beads to Suppress RFI:  
by KG6AMW on February 26, 2004 Mail this to a friend!
From the Amidon website, "The 43 material is a good all around material for most RFI problems. However the lower frequencies from . 5 to 10MHz can best be served with the 'J' material. The 77 material can provide excellent attenuation of RFI caused by amateur radio frequencies from 2 to 30 MHz. and the 43 material is best for everything above 30 MHz. However, it is still very effective across the entire amateur band but not quite as good as the 77 material. The 73 material is specifically a ferrite bead material having a permeability of 2500 and can provide RF attenuation very similar to the 77 core material."

 
RE: The Proper Split Beads to Suppress RFI:  
by WB5HZE on February 26, 2004 Mail this to a friend!
I wonder how well a choke using a mix of #43 and #77 beads would perform (a string of #43 beads followed by a string of #77 beads, or possibly mixed evenly)? Has anyone tried this? I would think that combining the two types would require less material than two separate chokes in series & would perform acceptably 160M thru 10M. What might the downside be?

My own application for such a "broadband" choke might be behind the lightning protection at my shack entrance, on a coaxial cable running to a remote antenna switch (connected to a variety of different antennas 160M thru 10M).

The #31 material is interesting but it appears that there is little choice in sizes.
 
RE: The Proper Split Beads to Suppress RFI:  
by KC8VWM on February 27, 2004 Mail this to a friend!


Mike Czuhajewski WA8MCQ has this excellent chart for toroids, print it out.

http://www.electronics-tutorials.com/basics/toroidcharts_mcq.htm


>>>RF-Toroid was written as a supplement to the Micrometals RF Application catalog. Much emphasis was put into calculating the location of the Self resonate frequencies for series and shunt inductors. RF-Toroid is for use DC to 300 MHz.<<<<

Source:

http://www.electronics-tutorials.com/basics/toroids.htm

73

Charles - KC8VWM
 
RE: The Proper Split Beads to Suppress RFI:  
by KC8VWM on February 27, 2004 Mail this to a friend!

Toroids - cheap, cheap, cheap...

http://partsandkits.com/toroids.asp

73

Charles - KC8VWM
 
RE: The Proper Split Beads to Suppress RFI:  
by KC8VWM on February 27, 2004 Mail this to a friend!

Another good source - snap on beads
All made with 43 Material, effective DC-200 MHz!


http://www.surplussales.com/FerSplit/FerSplit-1.html
 
The Proper Split Beads to Suppress RFI:  
by N0GV on February 27, 2004 Mail this to a friend!
Very nice article -- Just a comment as to cost vs. effectiveness....

At about 2-5$ each for snap together beads you might want to consider that if you need more than 4 on a single line a toroid with 3 or more turns might be a better choice -- type J, 77 or 73 for HF, type 43 for 50MHz and up.....

My worst case problems are usually solved by a $12 toroid with 5 turns of LMR-240 thru it and a couple of connectors on it for rf on co-ax or just a toroid with N>7 turns of whatever offending wire was radiating thru it.... this tends to be as effective as 16-50 split beads (yes sixteen to fifty split beads) at supressing rf from the exterior of the shield in co-ax or from the offending wire that is radiating noise.....

As a member mentioned the inductance of a coil is proportional to the square of the number of turns and a bead is a one-turn device generally....

Makes a great 1:1 current balun too.... ;)

Grover Larkins
 
RE: The Proper Split Beads to Suppress RFI:  
by KC8VWM on February 28, 2004 Mail this to a friend!
Thats a good point Grover, sometimes torroids are more cost effective and they often behave differently than ferrite beads in resolving interference.

Torroids are generally "more" recommended in TVI situations. I generally use beads to suppress any station RFI (RF outbound) and torroids to supress any TVI.(RF inbound)

73

Charles - KC8VWM
 
The Proper Split Beads to Suppress RFI:  
by WB5ALI on March 3, 2004 Mail this to a friend!
Excellent article. Very useful. Thanks and 73

Mark, WB5ALI
 
The Proper Split Beads to Suppress RFI:  
by N6KJ on March 3, 2004 Mail this to a friend!
I prefer Mix 77 for HF RFI suppression, esp. 80
and 40 meters. I've searched numerous times for
mix 77 split ferrite beads, but have never found
any. Anyone know where you can find Mix 77 split
beads?
 
The Proper Split Beads to Suppress RFI:  
by W6WO on March 4, 2004 Mail this to a friend!
I have made measurements and plotted the results of combinations of mix 43 and mix 73 ferrite torroids as common-mode chokes for low and high HF bands. I could email a copy of the results as a MS Word document to anyone interested
 
RE: The Proper Split Beads to Suppress RFI:  
by VE2XQQ on March 4, 2004 Mail this to a friend!
I think Palomar has some mix 77 stuff
look here:
http://www.palomar-engineers.com/Ferrite_Beads/ferrite_beads.html
 
RE: The Proper Split Beads to Suppress RFI:  
by VE6XX on March 7, 2004 Mail this to a friend!
Greetings All: Allan & Tom.....you are both to be thanked & congratulated for this timely, interesting & informative article. It is SO refreshing to read something of this calibre(yeah, I know, we Canadians spell funny) without having to wade through tirades from from those who can't disagree without becoming disagreeable. There does seem to be some disagreement regarding the efficacy of type 43 vs type 77, or type "J", but I suspect it is a case of honest men sometimes disagreeing. Doubtless each RFI case is an individual problem with it's own unique solution & one type may work better for that specific case. That having been said, Allan & Tom's article gives us a selection of types from which to choose, & possibly the gentleman who suggested the intermixing of types may have something. It would be illuminating to put the theory to the test. My thanks to ALL respondents for kudos to the authors, & positive, consructive replies.
I look forward to more articles of this nature. It is marvellous to see comments & suggestions & advisements coming from readers which expand the usefulness of the original article. Well done gentlemen!
CHEERS! Brian, VE6XX
 
The Proper Split Beads to Suppress RFI:  
by W7HJ on March 7, 2004 Mail this to a friend!
BZ (Navy speak for Well Done !) Alan. I have been wanting to go mobile in my 500SEL for several months but popped a fuel pump module and a fuel pump by HF RFI and VHF RFI, respectively, in my older 280SE and have paid the unspeakable repair costs to get the ol' car running again, TWICE !! Before I take the plunge off the deep end and do beads with the 500SEL do you know if any of the car manufacturer's can make recommendations for how to go about suppressing RFI ? I can't help thinking that GM must do something with their Hummers before the military light off their HF equipment, and police cars around the world must have some type of VHF suppression built-in. Any thoughts on this before I do a letter to Mercedes ?

73,
Harley W7HJ
 
RE: The Proper Split Beads to Suppress RFI:  
by K0BG on March 9, 2004 Mail this to a friend!
Harley, I don't know why you think you zapped the fuel parts in your 280 with RF. If you did, this is the first case I've ever heard of. M-B (now D-C) have always done a good job of protecting their various electronics from any source including EMP and RFI. Diesels can be quieter than a standard spark engine, but a lot of the new stuff including D-C?s newest diesels have electronic injectors and they are noisier then some ignition systems.

I've had great success with beads on injectors and COP units, as well as the rest of the various RFI producing parts of vehicles. However, this is just one aspect and other RFI reducing schemes are necessary. These include, but are not limited to, tail and exhaust pipe strapping, hood, trunk, and door strapping, and using low-impedance wiring (read that LARGE sized power cables.

Alan, KØBG
 
RE: The Proper Split Beads to Suppress RFI:  
by K1DA on September 20, 2005 Mail this to a friend!
AMerican General still makes military Hummers and they are diesel. GM makes look alikes under license for poseurs. The difference: the military version uses a drive system which places the diff units well up under the body for better ground clearence. The GM version is built on a pick up truck with the diffs right out there in the middle of the solid axle where they can bottom out.
 
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