Can Ferrite Beads Really Help?
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- Опубликовано: 9 окт 2023
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Welcome to our latest RF experiment! In this video, we're diving deep into the world of RF chokes and common mode current attenuation. Have you ever wondered if increasing the number of ferrite beads in an RF choke can yield better results in reducing common mode currents? Well, we did, and today, we're putting it to the test!
Common mode currents can wreak havoc in RF circuits, causing interference, signal degradation, and even damage to sensitive equipment. RF chokes with ferrite beads are commonly used to combat this issue, but the optimal number of beads for maximum attenuation is a question that many RF enthusiasts have.
In this video, we'll walk you through our experimental setup of an RF choke with varying quantities of ferrite beads. We'll explain the theory behind RF chokes and common mode currents and provide a detailed overview of our testing methodology.
Throughout the video, you'll witness the results of our experiments, as we measure and compare the attenuation of common mode currents for different numbers of ferrite beads. Will more ferrite beads equate to better common mode current suppression? Or is there an optimal quantity that strikes the perfect balance?
Join us on this scientific journey as we explore the fascinating world of RF chokes, ferrite beads, and their impact on common mode current attenuation. Whether you're a seasoned RF engineer or just a curious enthusiast, this video will offer valuable insights and practical knowledge.
Don't forget to like, subscribe, and hit the notification bell to stay updated with our latest experiments and RF-related content. If you have any questions or suggestions, please leave them in the comments section below. Let's unravel the mysteries of RF chokes together!
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Hi, when you say attenuation, it implies a negative sign.
When you talk about gain, you don't mention a positive sign because it is understood.
You were repeatedly telling, " so many dB negative attenuation though it is unintentional, I believe.
De VU2RZA
That is a fair point, thank you for pointing it out. I am still working on the imposter syndrome. I suck at public speaking and YT has been the venue to get past it.
@@GraymanPOTA thanks and I very well appreciate it 👍❤️
De VU2RZA
I had a little different reason for watching your video - I suspect that my household 120 Volt electrical system has some higher or lower frequency or frequencies that is\are running mixed in with the 60 Hertz. It shows up only as big spike 70-100 Volts Per Square Meter of EF on my various measurement devices when I move around in the room physically - (meters are the Tri-Field with the chickenhead selector knob and the GQ-360V2). The frequencies could be below 60 Hertz or above and even way above limited only by what could run on a wire of that length, Anyway since I don't know the frequency it is difficult to know how to try and reduce it. I know Tripp-Lite and others sell power conditioners but the range of frequencies they claim to snub are limited. So was thinking I might reduce them using passive chokes just snapped on over the 12/3 Romex.
@@policedog4030 unfortunately, with all of the devices that we have in and around our homes, RFI shows up all over the place. What type of issues are you experiencing? If you are experiencing RFI on devices, it is best to clamp ferrites close to the device that is experiencing the issue.
This is exactly the setup and test I had in my mind and wanted to see. Very useful results. I appreciate you doing this test. 73
1:45 in and I can already appreciate how your Zerro mat is almost perfectly square with the shot.
You can’t even begin to imagine the mental agony that caused me. I might have recorded that segment more then once
LOL
And now I’ve watched the whole video. Really cool man! That was an awesome demonstration.
Thank you Mike and thank you for allowing me to use the excerpts from your video. 🌮🌮🌮
You've answered my curiosity regarding ferrites, Thanks. I keep all the ferrite beads off data and monitor leads for example. I don't know what mix they are, but I'll be sliding some down my coax sometime soon, hopefully with the required effect. 73 de Mark GØUSL
Thanks for this great test👍
Thanks Tim. As a follow up, you should compare a Mix 31 FT240 Core with 7 wraps of coax vs the beads and see which one applies more Common Mode choking impedance.
That is a great suggestion. I am looking at building an open air choke/ugly balun and using the test rig to see the relationship between adding and removing coils of coax has on the attenuation across the HF frequencies.
I am also looking at using the rig to see the relationship on adding and removing turns through a toroid. You should also be able to see how the turns and their spacing affects the attenuation.
I second that test!!!! I use the 12 turns around a 240 mix 61 toroid and it works great. BUT it’s awesome to see scientific results!!👍🏼
The test rig in conjunction with the NanoVNA makes a great visual aid to help understand the relationship of the number of passes of the coax through the center of the toroid to the effective attenuation. Thank you for watching.
This would be a great test. My understanding is that you get a better than linear improvement in rejection by adding wraps compared to passing the cable through more cores, so that would imply you're better off with one big core you can loop the wire through multiple times (at the cost of a bit of feed length) rather than a bunch of clip-on cores only large enough for the coax to pass through once.
I had click read more after "7 wraps" and was expecting a Taco Bell joke 😆
What fun! Well done!
Sweet Test, Thank You !
Excellent video! Wow ... nice and clear! Thank you very much on this explanation! 73
Excellent information. Answered my questions. Great depiction of diminishing returns.
Thank you. I hope the video helped you.
Excellent demonstration of drawing conclusions based on the hard data. I'd love to see an overlay of the graphs with 3, 5, and 7 beads to visually see the difference in one image.
Thank you sir!
Thanks you! Greetings and support from Croatia!
Thank you for watching.
That was great TIM. with bigger coax best to use snap ferrite. trying to wrap Hyperflex 10 threw torrid not going to happen unless a very big core. this works on hard line as well. thank you for the link for that jig for the VNA . was going to make one. send one to smoking ape. he just did a video testing CMC chokes on a VNA H4. I use both ABR coax and M & P coax. I found a 9:1 is bad for CMC RF getting back to radio. I got extra long USB cable and wrap it threw a T 240-31 core. helps a bunch on FT8 or JS8 call. or and digital. I did my power lead to my IC 7300 and my laptop power leads . I choke every thing. the only thing that hurt is when choke DC leads have big enough wire AWG so not to get voltage drop. I go up a AWG or more when making DC chokes. 73's
An interesting test, actually a better result than I had expected. This W2DU approach is a poor use of ferrite. I played a lot with FT240-31 and FT240-43 cores wound with coax but as per the work by G3TXQ although they can offer a lot of common mode rejection the chokes tend to be relatively narrow bandwidth. By the time I had enough turns to offer reasonable attenuation on 160m the inter-winding capacitance is killing the 10m performance. My latest common mode chokes (only tested to a few hundred watts) use twisted pairs stripped from CAT5/6 cable, each pair is nominally 100ohm characteristic impedance, so I use 2 pairs in parallel. Common mode attenuation on 40m is 38dB yet remains close to 30dB at 1.5MHz and 30MHz. Insertion SWR and loss is good too. I do have pictures and saved plots...73
P.S the NanoVNA is a great tool, probably the best ham radio bargain I have ever purchased.
The video and the test kit was just to show the relationship between adding the beads to the coax and seeing the attenuation that it provides. I am hoping that it can become a visual teaching aid and give the ability for people to easily test different designs for the best outcome. Thank you for watching.
Nope, I don't want the test rig, this is why I like and subscribe, because you have done it for me.
Thanks, it's very useful information.
That was interesting, thanks!
Glad you enjoyed it!
When creating a multiband choke, it's advisable to use different types of ferrite cores based on their performance characteristics. Typically, ferrite cores designed for higher frequencies are placed at the end of the coaxial cable, directly before the antenna. This placement is chosen because higher-frequency ferrite cores exhibit less attenuation at lower frequencies, resulting in less heating when operating at those lower frequencies while still providing some degree of pre-attentuation. Consequently, ferrite cores designed for lower frequencies endure less strain.
In my setup, I utilize 15 cores of the 8W500 type (from Wuerth Electronics), with each core having a attentuation approximately 80 ohms at 1MHz and 100 ohms at 10MHz, providing about 1500 ohms of attentuation 80 meters. For frequencies at 10MHz and above, I employ 3W800 cores, which have dimensions of 7.3mm inner diameter, 28.5mm length, and 16mm outer diameter, providing a attentuation of 195 ohms at 25MHz and around 100 ohms at 10MHz, totaling approximately 2900 ohms in the 10-meter band.
Regardless, such a choke operates with minimal losses, delivering 3-5 kiloohms of attentuation across the 80-10 meter range (equivalent to roughly 40dB), and spans a length of 90cm, housed within an 17mm diameter brass tube for protection against UV and weather exposure. Coax i use is Aircell 7.
Thanks a bunch for doing this video. I run 4 on my 80-10 home brew EFHW. Always wondered exactly what results I was getting in the real world. Oddly, I thought it might have been a bit overkill. Apparently not. Thanks again!
Final thought: Would love to see a video with a longer jumper and see the reaction of the nano VNA if the ferrites were moved to different locations on the coax. watch the reaction as they are moved, see if being separated by larger distances from each other makes any difference or if they do indeed need to be close together sequentially. Does it need to be near wavelength zero nodes or at the height of the return wave? Thanks again! ... ohh.. and maybe 3 of one kind.. and 3 of another and and and... all on one coax to see if there is a more broad spectrum result. I'll shut the hell up now. :)
My hope with this video is to stimulate conversation and show people that there is a way to easily test their theories. Thanks for watching.
Could you do a straight through test of the affect of multiple toroids on differential current within the shield? And what is the affect of a CMC on a multi-band antenna (EFHW for example) with regard to high-band performance (on say 10 meters?)
Thanks.
Very nice test.
Thank you for watching.
See if it makes a difference on position if you put it at the end of the cable versus the beginning of the cable or if spacing them creates a difference
Would this theory work on a CB radio receiving RF noise from power inverter, refrigerator, maybe even computer or wifi? My concern would be the ferrites may hinder the receive strength of the antenna. Also, would it help to add ferrite to the outbound extensions of the inverter?
Nice video. Could you test turns around large choke ring for comparison?
That is on the list for upcoming videos. Thank you for watching.
thanks
I am waiting ordered mine
Nice, useful experiment, thanks. I always wondered. Of course my pedant is saying that you should not be saying 'negative 20dB of attenuation' - correctly the attenuation is not a negative. You have neg dB of signal, pos dB of attenuation. /pedant off
Thank you for the feedback. I inadvertently throw the double negatives in every once in awhile without thinking about what I am saying. It drives my wife nuts.
Tim very nice test,and my question is,for marine electronics fishfinder , they come with one ferrite bead that should be installed on the transducer cable. If more than one bead was connected, help to improve transducer feed back quality?
RFI has a way of finding itself in places you do not want it. The fact that the manufacture has placed a ferrite bead on the transducer cable would be a good indication that RFI can be an issue. It would not hurt to try some additional clamp on beads and see what the results are. You do need to keep in mind, that the ferrites will not boost or amplify the signal from the transducer, but it will potentiality stop RFI from interfering with it. Also, there is a point of diminishing results with the amount of suppressions per added ferrite bead.
I design instrumentation, some of which works to 10GHz. I get through ferrites like you would not believe. This is on top of all sorts of faffery like 10,000 times oversampling to get an average which does average out some noise. Cooling everything down helps too. The guts work at -40C. The customer wants me to design some kit that will detect a -300dB signal at 100GHz. As far as I know that needs liquid helium cooling and electronics that can handle being that cold. The tolerances on the dish are nuts too. I'm trying to work out if a helical antenna would be easier. The wavelength is only 3mm.roughly. That said I really do not have a clue.
When designing instrumentation in general: Which software do you use to simulate? How do you take factors like induction of the circuit board in consideration? How many prototypes do you need to get your result?
I had been leaning toward using a toroidal design for RFI suppression but your video has me now considering snap-on cores. I understand your cores were Mix 31 material. Have you tested the same setup using Mix 43 material?
My next question is, what if you alternated 10 cores on the test coax? For example, would a string of 31-31-31-31-31-43-43-43-43-43 show any difference than alternating 31-43-31-43-31-43-31-43-31-43 ??? Or in general, what does the VNA show when using Mix 43's instead of 31's ???
I am hoping for additional suppression below the 40m band, down to the 160m band, without a huge compromise in the higher frequencies. My target use is a multi-band "wire fan-dipole(s)" center fed with 50 ohm coax.
Those are all very good questions, that I will have to answer with the dreaded response of "it depends". The video was designed to show people how they could test various configurations for themselves as they experiment with different configurations relative to their specific use cases. Most amateur radio operators simply rely on information published on the Internet or from Carl down at the club who insists his way is the way to go. Most people will just take the information as gospel and move on. With some simple and inexpensive test equipment, we now have a way to not only validate Carl's advice, but also tune it to our specific use cases. Keep experimenting and thank you for watching.🌮🌮🌮
I couldn't find an answer to this question: where to put the ferrites? At the antenna, or at the radio? My personal experience shows that inserting a 1:1 current un-un at the radio had no effect. However, putting it at the 4:1 balun on the tower of my OCF dipole reduced the noise floor by 2 S-units on most bands. I don't understand how it works, but I like the reduced noise floor. Thanks for your video!
That is a good question that unfortunately has the answer, it depends... The variable being the use case of the antenna and the feedline. In an EFHW antenna, you are going to use the unbalanced coax as the counterpoise for the antenna, so you would want to put the ferrites on the radio side to choke off the common mode current that is picked up on the coax so it is not introduced to the radio. If you place the ferrites at the feedpoint of the antenna, they would choke off the common mode current at the coax and the coax could not be used for the counterpoise. Some EFHW antennas, have a place to connect a counterpoise, but then effectively you are changing the antenna to a CF or OCF dipole depending on how long your main element and counterpose is. Depending on how long your coax is and some other factors, it is possible to pick up common mode current between the choke mode choke at the feedpoint and the radio. I always place a common mode choke at the radio. It will not impact the desired RF signal on the coax.
Thank you, very Interesting. Who manufactured or supplied the mix 31 beads? Fair Rite, Amidon, RF Parts, Palomar Engineers or an Amazon undefined vendor?
The ones I used in the video were made by Fair Rite that I purchased from Mouser.
will adding ferrites beads ( 5 or more ) along the coax do the same thing as a choke? Bulding a choke takes more time.
2-5KOhms, thats the way to go, depending on your antenna. A symmetrical dipole doesn't need a lot of beads, off center fed stuff, GP's >2Kohm or more.
Great video.
Question: How far from the connection (SO239) to radio should ferrite beads be placed?
Should I add one bead at a time or should I just put all 7 beads?
RG8x coax and 11mm ferrite beads.
That would depend on primarily on the type of antenna that you are using. For example if you are using an EFHW, you want to use the coax as the counter poise so you would put it close to the radio. In other cases you could place the choke closer to the feed point of the antenna. Then depending on how much coax you have between the radio and the antenna there is nothing wrong with placing RF chokes at both ends. Common mode current chokes do not interfere with the signal on the center conductor of the coax, it only chokes or attenuates the current flowing on the outside of the coax in a common direction as the current on the return shielding of the coax.
As for the distance between them, that is where the test rig and the NanoVNA come in to play. There are several designs out there and everyone provides different results. Some are better than others. This is a simple way to visually to see the results in realtime as you make those adjustments. I am working on the next video where you wrap coax through a toroid each time you pass the coax thru the center you will get more attenuation, but what is the best number of turns.
Let me explain setup: I have a 20m EFHW antenna on my roof and a ATAS-120A antenna on my chicken coop roof which works pretty good as a counterpoise both antennas are connected to a 2-position coaxial switch which is than connected to FT-891 HF radio. Both cables are RG8x and about 50ft. each.
Will ferrites beads work with these setup?
Is is best to individually connect each antenna's coax to radio, adding beads where you mentioned.@@GraymanPOTA
@YayaOrchid I would think that the best place would be to place them on the cable between the switch and the radio. That way you would benefit from the same choke on both antennas.
Thank you, I will add all 7 and see what happens.
73@@GraymanPOTA
With that test rig and the nanoVNA can you come up with a way to find what composition a known choke is?
I don't think so, but I did find a decent video from Fair-Rite on how to generally identify an unknown ferrite core with some basic test equipment.
ruclips.net/video/Q95Vwk3kZok/видео.html
SMPS adaptor of the external amplispeaker for my laptop produces RFI bands in my radio on multiple bands. Will be seen as broad 'waterfall' bands much wider than an SSB signal. Took me a long time to find the culprit! Wonder whether Ferrite Beads will help? 73 de Jon, VU2JO
Very nice test. How about a similar test but at 10m, 6m, 2m & 70cm with Type 61 snap on ferrite chokes. Not all hams do HF. Judging from your data, attenuation per choke increases with decreasing wavelength, but how much? Is one Type 61 choke "enough" for a 70cm antenna feed? (Type 31 ferrite is not recommended for higher frequencies.)
You are right, the different compositions of the ferrites will produce different results at different frequencies. The motivation behind the video wasn’t to show people what the different results would be, it was to teach people how they could test the effectiveness of common mode current chokes with some simple and inexpensive test equipment.
I would like to see you assemble the rig on another video
I recorded the build process. I will work on getting it edited down for a future video. Thanks for watching.
Would have really added to the content if you had done a simple tabulation of the data and gotten excel to draw some trend lines through them from 1-7 chokes
I can appreciate that, but the video was about showing people who they could use simple inexpensive test equipment to test, build or confirm the effectiveness of RF chokes.
I think I must get my hands on a nano VNA.
I have made a coax cable with around 30 ferrites of different absorption properties together with some iron powder ring ferrites for a measurement cable. However, I never measured the attenuation. I merely believe it should be good.
You were the person I had in mind when I made the video. We get told by various sources all kinds of different ways to build a choke, some right and some wrong. This is a good way to test and modify the specific choke in front of you. Not to mention the Nano VNA has a lot of uses in ham radio. The NanoVNA that is linked in the video description currently has a 10% off coupon.
@@GraymanPOTA 73 and 55 in 2024 mate, from a German oldie. Love your video!
Ok so now let me understand something.. when we attenuate with ferrites what do we attenuate specifically? The reception signal, a noise that is causing qrn/qrm to the cable near our radio ? Nice experiment... Will do the same with my NanoVNA in realtime with my radio
In an unbalanced feed line, like coax, we have current traveling in differential mode or opposite directions between the center conductor and the shield. Because the feed line is unbalanced, generally due to different lengths of conductors, the magnetic fields of the signals do not cancel each other out allowing a magnetic to be established and allow RF or referred to as common mode RF to travel down the coax and in to your radio. With the ferrites, you would be attenuating the common mode RF that is riding in the magnetic field by collapsing the magnetic fields before the radio. At best, common mode RF will cause excessive static and elevated noise floor and at worst, it could cause damage to the radio. It is always a good idea to use a common mode RF choke right before the radio.
Interesting, I tried to duplicate your results, same rig, mix 31 tight fitting beads from Fair-rite and only got about half the reduction you got. I have some slip on's on order and will see if those do any better.
I think you stumbled on to a good reason why people, end users, should have the knowledge with test equipment to test the effectiveness of common mode current chokes and other components that we use in ham radio. We have become a turn-key society where we just expect things to work, but we don't understand how it works. That is OK, the hobby has shifted that way over the past 20 years, where people not required to be as technical because so much pre-built and designed gear is available. I am glad to see that you are attempting to duplicate the test. Did you do the OSL calibration of the VNA before you tested the circuit?
Please show us more about that test rig.
I recorded the kit build and I am getting the materials together to use the test rig to build and test an open air choke/ugly balun. Thanks for watching.
I think a larger ferrite and passing the coax thru it 2 or 3 times would be more elegant. Or spare the ferrites and wind a tight 6-7 turn coil and secure with tyraps.
The test rig an NanoVNA makes it testing different configurations so you can get the best performance results from your setup. Thank you for watching.
How does placement at the rig side or antenna side or both make a difference or have an affect?
It depends on the type of antenna and the use case, but I n all cases, closest to the radio is the best.
The test must be carried on with full power not 0.1 mw (-10 dbm).nice video.congratulations.
20 more and you have a ferriet cable ... but very nice to see what ferriet is doing and how much till you get no return thnks
I am going to do a series of these videos to show people how they can validate stuff when Ole Vern down at the club tells them this is how you must do “X”, but can’t tell you why. Thank you for watching.
@@GraymanPOTA i am inn !!
Nice to see some practical experiment which is easy to understand. However, I would have liked to have seen 160 m included in the measurements. I would also like to see other MIX than 31, such as Mix-43, and others, as it is a bit surprising that Mix-31 covers the entire HF band so relatively well, but maybe there would be other MIX that could do it better than this ??
The test covered for 1 MHZ to 30 MHZ, I just highlighted the 40,20 and 10 meter bands as a point of reference. If you look at the left side of the trace, you will see the lower bands.
I have some Mix 43 ferrite beads, but they generally provide the best attenuation above 30 MHZ. Due to the mixture of different compounds use for ferrites and toroids, they provide different characteristics for a wide variation of applications.
I will be doing some different videos with the test rig to demonstrate the different properties of different types of chokes so people can see what works best and tune them for their specific use case.
Thank you for watching.
I did see the start at 1 MHz, bit as the lowest band in this case, normal will be 160m, and the highest vil bee 10 m, then i do think that the ends makes most sense to show up, and special to show the difference of what can be expected for a comparison, so i do look forward to see more test, of other MIX.
Also the test fixture that you are using, will be nice to have more details on.
Nice video! 73, Mike KF8OD
Because of the amount of people who swear by chokes, I feel like I must be wrong - BUT......
You send voltage up the coax which results in a current which drives the antenna.
If the antenna / feeder is right, there will be no common mode current, and if the antenna / feeder is "wrong" there is likely to be common mode current.
Isn't it the case that a choke is totally relying on the fact that it is an awful transformer, with nothing to couple the energy to, which then results in heating in the core? The heating doesn't come for free - that is your radio output power being used to heat a lump of ferrite.
If you have a fixed antenna that is "not quite right" but you are prepared to accept this, and you ALSO have trouble with the resultant common mode current causing interference in the shack, I can see how a choke would stop the interference, but that is ALL it does.
What the choke does not do (and this is what I feel is missing from most demonstrations) is turn a non-ideal antenna with current problems into a well functioning antenna.
The current that should have manifested as RF power from the antenna is simply wasted as heating power instead.
Again - it could be that you live with some restrictions. Maybe your garden is only a certain length. Maybe you have limited mobility and a friend helped you erect the antenna 10 years ago. Maybe you hid a wire in a flagpole which is now set in concrete. Whatever the reason, you end up with a non-ideal antenna / feeder arrangement that returns current to the shack. A choke of any kind simply burns off the current as heat to stop it from ending up in the shack.
No?
If you use a non balanced feed line you are creating the conditions to prevent the differential mode current from canceling out the magnetic field that carries common mode current back to the radio.
There is more to this. One, that test jig is going to introduce a good bit of parasitic capacitance and skew the results. Anyway, you're not measuring the impedance along with the resistive and reactive components of the impedance. Each bead will actually add the same amount of all 3 of those, every time. What you have there is almost certainly reactive for 80 meters which can make common mode current worse at those frequencies than no choke at all. It's probably resistive and will work well for 40 meters and above but without measuring you can't know that for certain.
Thank you for watching. I look forward to seeing your video.
What happens if half on each end or spreading them out evenly ? Does it change anything??
Good question, depending on how you use your coax will depend on whether you place an RF choke on at the coax at the feed point or not. For example, on an EFHW antenna, generally there is no counterpoise and the coax would act as the counterpoise for the antenna. In this example if you placed an RF choke at the feed point, you would lose any benefit of using the coax as the counterpoise. As for other examples, it really depends on the environment you are operating in. It will certainly not hurt, but depending on the length of the coax, it might not help.
There are several designs for making RF chokes on the internet, some good and some not so good. I was using this one example to show people how they could use the common mode current test rig and the NanoVNA as a way to test different designs and see which one worked best for their specific use case.
I'd like to see this test repeated, but with a longer length of coax, say some significant fraction of a wavelength at 40m, and move the ferrites around on the coax. There should be nodal points on the coax where the current will be low but the voltage will be high, and vice versa, and the position of these points should be different for each wavelength. You should find the effectiveness of the ferrites will vary depending on where you position them. That would be very informative.
I thank you for your suggestions, but the point the video was to encourage people that they could, with some simple inexpensive test equipment, build and test their own RF chokes.
Also, why doesn't your sweep at first show a flat line on 0dB?
My assumption is that there’s an inherent amount of differential mode current suppression that is happening without adding any external suspension to the circuit.
@@GraymanPOTA Can you explain to me what "differential mode current suppression" is? I thought we were trying to do with common mode and not differential mode.
Looks like 80m needs a lot of ferrites. Or a different solution (toroid?)!
wrap the coax around a grounded iron pool. 20 turns on a 3" tube is ok.
why stop at 7? why not see what happens with more, if it continues to attenuate, or if more just stops working. I don't know anything so excuse my question if it's offbase.
That is a fair question. At some point you reach the point where the amount of attenuation you gain per ferite becomes negligible. In this application, the once you achieve -20 db or more of attenuation, you will effectively choke off the common mode current from feeding back in to the radio.
What kind and where did you get them
I used Mix 31 snap on ferrites from Fair-Rite. These have a 9 mm inner diameter and RG8X coax is around 7 mm outer diameter. They will slide a bit depending on the diameter of the coax you are using. On the manufactured versions, they will slip over some shrink tubing to help keep them together and in place on the cable.
www.mouser.com/ProductDetail/Fair-Rite/0431178281?qs=JTtBSkyWskgca1F4cZ1wag%3D%3D&countryCode=US¤cyCode=USD
Hello!
Please can you tell me where I can obtain such common mode test rig?
73 de PD2JHP
Common Mode Current Choke Test Rig - electronics.halibut.com/product/common-mode-current-choke-test-rig/
Thanks for watching.
Thanks for these tests. N0QFT
Glad you like them! Thank you for watching.
THAT USING DIY FERRITE BEAD COIL ANTENNA BOOSTER
What do you think the results would have been if you'd put them at each end, instead of only at one end?
Good question. The attenuation effect of the ferrites are cumulative, but at some distance if your ferrites are to far apart, you stand the risk of reintroducing RFI back on to the coax. In some use cases, you might want to place ferrites on both ends of the coax, but in the case of an EFHW antenna, you are going to use part of the coax to act as a counterpoise for the antenna so you would not want to place any ferrites on the feedpoint side.
@@GraymanPOTA Thank you 😊
Hi, I wonder if the ferrite beads would have the same effect with 240 volt AC?
That is a good question. RFI can find it's way in to a lot of things, for example, I have issues with my oven in the kitchen on the other side of the house doing silly things when I am on 40 meters and I am transmitting above 50 watts. When you are asking about 240 VAC, I am going to assume your use case is the input power supply for an RF amplifier, but it could easily be an electric dryer or electric stove. Palomar Engineers, palomar-engineers.com/, has a whole section dedicated to HF RF amplifiers and has kits put together for specific amplifiers. Even if your specific use case is not listed, there is enough documentation and diagrams for you to get a good idea for a solution to meet your needs. In addition, they have solutions for other RFI issues in the home. In full disclosure, I have not personally purchased anything from Palomar Engineers, but I know people who have. I have not heard anything about the company or their solutions that would make me want to shy away from making a purchase from them. I hope this helps. -Tim
@@GraymanPOTA Thank you for the reply, my specific issue is having just fitted 240V LED lights, it cuts my boradband speed down by 30% when the lights are on. The broadband it interupts is supplied by wifi repeaters and to the be of my limited knowledge they do not like any interference on the line.
@@ezetobebad it appears that the LEDs themselves might be generating the RFI and I don’t think that placing RFI suppression on their inputs would help out. It sounds like you can measure a difference in interference with and with the lights turned on. I would speculate that the LEDs are interfering with the WIFI signal on the 2.4 or 5 GHz band between the device and the AP or AP to AP if you’re using a MESH configuration. Another scenario might be the WIFI AP is in close proximity and it is being affected by the RFI. My educated guess is that you are experiencing interference in the signal between your device and the AP causing excessive retries and slowing down the speeds. I would try using a different channel in the same band and/or try a different band and see if that helps out. Most APs have a periodic scan function to find the best channel within the band on both the 2.4 and 5 GHz bands which may or may not help if the lights are not on at the time the scan happens. I hope this helps guide you to a solution.
Thanks for the suggestion, very helpful. godbless@@GraymanPOTA
how many licks does it take to get to the middle of a tootsie roll pop LOL :)
It’s funny that you said that. I am working out my next video about how many turns of coax thru a toroid does it take to become an effective RF choke. I was trying to figure out how to work that in.
Like and comment to help the channel.
Man I sincerely appreciate this, but a test bed is not a true use case, do this to replicate a real world scenario:buy a uniden bearcat scanner, preferrably a bcd536hp, turn it on, turn on your nearby HF SDR receiver and watch the QRM destroy your hopes and dreams. i mean all of them, Grayman. Now slap beads on that power supply one at a time until you reach 17 like I had at once and see that indeed there are no more hopes and dreams, and the only way out is not a visit to the gun store for a relevant amount or ordinance (I mean who needs witnesses anyway?) but a highly directional magloop instead, realizing all the money I ever spent on ferrite beads have gone absolutely to waste. I sincerely hope the ferrite family enjoys their college education :) great work, Grayman.
The first time I tried this experiment with the test rig and the NanoVNA, I bought some ferrite beads off of Amazon that said they were great for RFI, ham radio and all that jazz. What I found was that the beads did not provide hardly and attenuation in the frequency range that I was looking for. They did provide better attenuation at higher frequencies (VHF). The only thing that I conclude was that they were not Mix 31 ferrites. I looked at the listing that I purchased from along with several others and none of them listed a Mix type. I ordered a new set of 10 from an electrical supply house, that I could guarantee were Mix 31, and I got the results that I show in the video. Thank you for watching...
Why don't you also check the center conductor in a separate test?
We are looking at suppressing common mode current that is in the magnetic field of the shield. The center conductor carries differential mode current in relationship to the shield and we would not want to suppress that.
@@GraymanPOTAIndeed, you give an excellent reason to also check the center conductor in a separate test. We need to assure there's no attenuation there while adding the ferrites.
I'd like to know the effect of spacing the beads.
That sounds like a great follow up video idea. That is a good use of the test rig and nanoVNA to visually see the effectiveness of experimentation. What is your hypothesis on the effect of spacing the ferrites apart?
@@GraymanPOTA If there's any significant flux linkage bead to bead, then effective inductance, and, thus, suppression might be reduced. But spacing will make the assembly more flexible, and thus more durable, and the trade off is worth understanding.
But, also, we don't use these in isolation and, particularly for feed point chokes, the coax is in the near field of the antenna. Breaking the coax into non-resonant lengths might improve things in ways that don't show up in the simple attenuation tests. So, if one doesn't loose a lot of attenuation by spacing, it could reduce the effect of the presence of the feed, acting as a parasitic element, upon the antenna pattern.
@@KeepEvery1GuessingI made one from solid beads that were a tight fit on RG58. Threaded 12 on (10mm long each) with gaps to keep it flexible, covered it with adhesive heatshrink. I use it as a patch cable between my radio and antenna switch. It really does work.
I predict no effect
@@stargazer7644 I actually tried it! There was no difference.
I am interested not sure if I understand it all
Larry, the good news is you are interested. The long and short is that we get what is called common mode current that is developed on the outside of the coax feed line from the radio to the antenna. Coax is an unbalanced feedline due to the fact that the braid/shield of the cable is longer then the center conductor. Because the conductors are not balanced in length, it creates a situation where current is allowed to flow, in the magnetic field, the same or common direction as the return currents on the braid/shield of the coax. This extra current creates noise and could damage the receiver. The ferrite chokes I was testing will help disrupt the magnetic field and choke or attenuate the current that is allowed to pass in the magnetic field. So I was showing visually with test rig and NanoVNA the relationship of the number of ferrite chokes to the level of attenuation of the common mode current that is gained.
My goal for this channel is to help explain the "why" behind the principles of radio and electronics so lay people can understand. All to often we get told by someone that, fill in the blank here, is what you have to do, but they can never explain the why behind it.
I've found ferrites about 30% effective but nano crystalline core around 99%.3Phi
That is the beauty of the test rig. It provides a way to objectively test different setups to see which is best.
Can you use cheaper Harbor Freight ferrites rather than Snap-on?😂
You could, but Harbor Freight will try to sell you the extended warranty.
Interested 🤔🤔😔😔
Why would someone feed the shield of his coax?
That is a fair question. With this test rig we are inserting a signal on the shield of the coax to simulate common mode current that would occur on the shield of the coax in order to test the effectiveness of the common mode current choke. In normal operations, we would want a non disrupted electrical pathway between the chassis of the radio and the non-radiating element of your antenna. I hope that clears up some confusion.
You wouldn't feed the shield, but your antenna would. When you go from unbalanced coax to a balanced antenna (like a dipole), it forces the antenna to send some of the signal back down the OUTSIDE of the coax shield turning it into a radiator and part of the antenna system. This is generally undesirable - though for some types of antenna it is a design feature. Putting a choke at the antenna will stop that signal on the shield and will stop the antenna from picking up interference on receive and skewing your pattern on transmit and getting RFI in your shack.
First video I've seen of yours, but that music won't make me come back
Please let me know when you publish your Master Class on making RUclips videos. Thanks for watching...
@@GraymanPOTA lol wow, hit a spot did it.... It's all good snowflake, I've already stopped RUclips recommending you
I didn't notice the music. It must not have been too bad.
@@stargazer7644 it might depend on the device. Some phones sound better than others... But videos like this just don't need music anyway, the content was good enough.. but seems the old dude is a snowflake. He could have said almost anything else.
Did you say taco or did you say taco?
All I needed to do is mention 🌮🌮🌮 to get you to watch my video. 😁
So . . . .9?
You said "purchased" very suspiciously at 2:14. Sounds like you were implying that you stole them. In my head I pictured you doing air quotes just out of frame.
Sometimes I insert pregnant pauses when I am thinking about something else. I am putting air quotes around this, "some people" will actually complain if they think that you have been given something to make a video with and don’t disclose it. Thank you for watching.