How Many Ferrite Beads on an HF Antenna? What is Coaxial Cable? What are Common Mode Currents?
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- Опубликовано: 16 июл 2022
- Six second delay at the beginning. Title was edited down to fit the number of characters.
Jim W6LG uses a device similar to that manufactured by Mark Smith at www.halibut.electronics.com. Jim has ordered that circuit board and will test it soon in a RUclips video. How many conductors are there in a typical coax cable? Where do common mode currents flow? 
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NEVER DOUBT, The "your Elmer" is so true, will always refer to these videos... as needed... Thanks Jim, these videos so very much appreciated !!!
Wow, 10 seems like a lot. Another option might be looping the coaxial cable around a ferrite ring several times.
Question answered at 10:00 for those looking for the info and know the rest of what he’s saying.
Thank you for your test. I have the equipment and will check myself because be all know the Chinese who are selling junk on amazon are sneaking in junk ferrite. That’s why some were bad. Same with the tea they send, half of it is just ground up grass now.
Another great video...Jim can u not just wind the coax to achieve the choke at the antenna? Hope to hear you on the band soon...73's NX8T JIM
Thanks Jim. Great to see you back and looking good and healthy. AG7UJ
This was well explained. Thank you very much Jim! I’m home brewing a vertical for static mobile use and was wanting to use beads to make the choke. This gave me the nod. 73zzz!
Thankyou Jim a great little video
Important subject, under exceptional conditions, very much appreciated, Halibut Electronics do indeed provide a great piece of test equipment.
👍 73.
( The New Choke Cookbook, is a great resource too).
Jim, another home run… great video!
Great subject Jim. Wish I had this info a year ago when I was starting out but I’m very happy to have it now. Keep up the good work!!
Wow, Jim. This is something I have always wondered about and you have answered it and more as I need to check to see if my beads are a 31 mix and fit tight against the coax. Thanks again! Alan KZ6B
Glad it was helpful! I was using 31 mix and some were defective. Maybe it was something that I did. I simply don't know. 73, Jim
This one makes the top 10 list! Great piece - really helps explain this concept. Thanks Jim ~ 73. KN6ETI
I wish everyone would teach in your manner
Jim I hope you feel better soon. Thanks again for a great video and all the valuable help you have given as I set up my first station ! All I want is the best sound I can get !! I just ordered rg-213 coax and now my questions on chokes have been answered ! Next up is finding a compatible antenna tuner that I can use with an Icom 735. I will do a lot of listening across the bands and then use the 735 some on 10 meters until I take the general test ! Best Wishes
Good video Jim! With regards to the ferrite beads - I believe that a K9YC put out the Choke Cookbook back in 2018 and he also found that the ferrites were not consistent in their testing he conducted. It's worth a read if you have time!
Hey thank you so much for the education on trying to straighten out my sons RFI problem due to high tension lines above house
Last fall, I invited a couple of my buddies up onto a hilltop near our home so I could show them my portable setup & truck mast. Spinning the dial, I come across “Whiskey Six…(slight hesitation)…Lima Golf”. I got giddy. But I couldn’t get through the pile. I would be honored if just once I could log “Whiskey Six….Lima Golf” into my QR-Zed.
Appreciate the Help. Very Good Idea, THANKYOU 👍
Also loop antennas, I use them on all my connections, works for me. 😊
Good stuff Jim! 4:1 Balun works great on my G5RV
Enjoy the visit and I hope nothing untoward comes of it due to the immunosuppression.
Thanks for the information. As with many others, I would like to know about looping through a toroid, looping through a snap-on, and yes, I believe solid works better due to the continuity of the magnetic lines of force. Is it then any different than a toroid?? Seems to me to then be a toroid on its side lol.
I did see odd results measuring with a vna when I added the toroid. It definitely appears to affect the frequency response. It makes sense, it makes a coil.
Great video Jim W6LG. Would you place the beads on the coax feed line at the radio or more closer to the antenna on the antenna feed line?
Jim I really need to find the video you did on calculating loss from using a tuner to correct SWR and all the corresponding loss in RF. You explained it perfect how the 100 W eventually diminished cycle after cycle. Done so well. I want to educated some folks with this valuable data. Had someone say just add power. No way to convince them of the actual theory. You are are appreciated. Trust your health is improving . Love all your presentations. Is there a list of all your presentation. You are the gold standard.
Richard
KC6ART
Hi Jim, good to see you still making videos. I have played around a lot with common mode chokes and have found measurements interesting. TBH I have not done much with small ferrite rings, I have generally used 2.4" type 31 or 43 toroids. I have wound them with varying numbers of turns of RG400 or similar ptfe coax. I found at best I could get about 35dB of attenuation (Ref 50 ohms) of common mode current. I did find that too many turns on either type of core worsened high frequency performance, presumably due to the capacitance between turns. About eight turns on an FT240-31 is in the right ballpark to cover 160-10m.. You might find it an interesting experiment, for HF bands I don't think small beads slipped over the coax W2DU style are very effective. 73
Ferrites are highly effective on coax, more effective than a coax coil choke. 73
@@GroundControl204 the "ugly" type chokes can do more harm than good.
Great video and thanks!
I assume because of your methodology that the result is independent on the type of antenna, of the variety you mention?
Would be interested in hearing about end-fed case
1'st, the snap ons are great for an RFI fix or for experiments but always use the solid equivalents when you have a choice. the solids are much cheaper as well. Means you have to be able to install a connector of course but every ham should be capable of doing that anyway. 2'nd, the impedance presented by the bead is proportional to the square of the turns going thru the bead, the cable thru the bead equals 1 turn, however the impedance presented by the bead goes up ~X4 when you put 2 turns thru the bead (bigger bead or smaller cable) or a toroidal core. Fair-Rite and others publish impedance Vs frequency Vs number of turns curves for each material, generally they show 1,3 & 5 turns........ 73. Mike, K1FNX near Boston
Thanks Jim
Jim, Palomar Engineers carry sets of snap on beads just for this purpose. I've arrived at the conclusion that putting chokes at the feed point, in the shack and in between (within reason) has paid off in better tuner performance (remote tuner), and improved noise suppression at the receiver. While coiled up coax (ugly "unun") is better than nothing, type 31 material has broader response curves and a cleaner installation. Yes, more money but these can be installed over time to fit any budget. Besides, what's the point of getting on the air if an operator has noise and wasting power?
Thanks for another excellent video!
Thanks for a clear video - good for a beginner like me. I've a question: theoretically-speaking, will ferrite beads fitted to LED lighting wiring reduce the interference in a nearby long wave radio? Thank you in advance.
Hi Jim,
That was a great demonstration. Wonder if the non snap on bead would be more effective. The audio in this video was much lower than usual. Had to crank up my Cambridge Soundworks volume control quite a bit. You and the family stay safe. 73 WJ3U
Great video Jim. Many HexBeam makers place 5 to 7 snap on ferrites just at the feed point coax on the center post. Does this mean that the ferrites used for a choke should "always" be at the feed point of the antenna? Also, Silent Key M. Walter Maxwell (W2DU) did strongly suggest the "W2DU Choke Balun" in his book "". He suggested slip on ferrite beads. Also he explained that unlike toroid cores, the beads do not become "heat soaked". I do believe The WireMan and Palomar Engineers do sell this choke as a kit. Lastly Jim, can you delve further into the EFHW comment you made? Thanks Art W1SWL
I'm new to all this, but what I gleaned from a couple of YT lectures by John Portune W6NBC, is that, in ham bands, the inductance of coax with ferrite bead(s) (or a wrapped ferrite toroid or a balun coil) is inversely proportional to frequency. Your test example was at 20m (15MHz) with 7 or 8 beads and you got 12dB reduction in common mode current (25% or unchoked current). Does this mean that if I am operating at 2m (150MHz) I would get the same reduction in common mode current with just one bead (assuming of course that ferrite performance is independent of frequency, which it isn't)?
I have a single Mix 31 snap-on with the coax making 6-7 passes in a loop. Is that roughly the same as having 6-7 beads in tandem on a straight piece of coax? Or do the loops add a capacitive element, too? My Rigblaster interface freezes during FT8, but only on 20m and only occasionally. Therefore, I still think I may have a tiny bit of common mode on 20m... it's only noticeable with the Rigblaster (voice is fine). I find myself considering a second bead snapped on the same loop to "double" the choke's effect. Will it work that way? Thanks! -Scott, KE4WMF
I'd be interested in a comparison to 31 Mix toroid rings whereby the coax is looped through N times.
Dear Jim, I really enjoy your videos. I'm preparing to mount an antenna in my attic and I have a question. Does the "type" of ferrite bead I use matter? For example, do I want to use "#31" beads? What prompted my question is when I made the balun for my antenna, the plans called for a specific type of toroid (mix #43).
Just out of curiosity, would a large number of RF chokes eventually lower the RX incoming signal? I am using a mix 31 and mix 43 - FT240 toroids in series at the antenna feeding point and a mix 31 - FT240 toroid by the rig + 6 beads on an Ultraflex 10 feeder
I see most examples of common mode chokes being used in the field. They are using a short piece of coax and from five to seven cores with heat shrink tubing, installed right at the transmitter. Is the most effective location either portable or base? Is the last thing before it leaves the shack to the antenna? Thank you in advance for your valuable advice. 73 de W3LU
Thank you, very interesting. I've often wondered about this. My question is do you place them on touching end to end or can you have spaces between them?
No. Stack them up and form a large lump impedance. 73, Jim
Hello Jim. Great to see and hear you. Excellent video as always. I never have used the beads because I didn't know if they worked. I always built the 1:1 on the FT 240-43 with 2 cores and PTFE wire like Peter demonstrates on the TRX Lab channel for 30 dB attenuation. This looks soooo simple, costs less and much quicker. 73 sir. Stay cool and healthy.
Jim - Another great video and I have ordered the CMCC test kit from Mark at Halibut. When you have a moment, could you recommend a Nano VNA model to use it it? I see there are several variations. TU! Mike
use "with" it?
When adding this many beads is there any attenuation on your tx and rx signals? Would also be nice to see the experiment done with different mixes of ferrite.
I placed one at the aerial at first but had r.f. lower down so I put it near the radio. R.f. higher up now so I'm buying more and put one at both places.
Is there a right position near the aerial? At the aerial? One foot away? Two feet away? I wonder because r.f. might be stopped at the aerial but picked up on the coax halfway down. No radio books I have tell it, they just say use a balun or ferrite rings.
Interestingly one aerial manufacturer says at the aerial and another says at the radio.
How's this for an idea, coax braid made impregnated with ferrite!
G4GHB.
I'm curious about the efhw...will adding ferrites beads ( 5 or more ) along the coax close to tx/rx do the same thing as a choke in order to prevent cmc with an efhw as well?
I don't think the EFHW has any problems carrying currents on the shield because the feedpoint is a DC short where everything is bonded to ground. Grounding kills those "common mode currents" I'm guessing. Antennae are complicated so I never speak of them in absolutes. But I do love the grounded aspect of the EFHW since having some near lightning strikes with no run-in on my rig at all. Was fully connected at the time. Blew my fence-charger and my mind, but the radios were fine. One on a J-pole the other on efhw, all bonded at the feed point and entrance.
how many chokes can you have? can I have one at the antenna, another in the shack and maybe a third somewhere along the length of the coax?
Thanks for the informative video and for suffering the heat to make it "legible" (I didn't hear the previous vid but can imagine :) ) KF5THB
Question: there seems to be a broad range in quality; any recommendations as to what companies make the best ferrite beads?
Palomar was good. Look at mix 31 as a place to start. 73, Jim W6LG
I have always took a 6" outside dia pvc and did 4 to 6 turns of cable. The PVC allowed me to keep the winding close together and it kept the loops constant. By doing this would there still be a need for Ferrite Beads?
My simple tests showed that the coil of coax worked fine. When I clamped on beads, it got very narrow banded. It looked like something with a high Q. 73, Jim
@@ham-radio I had the same question. Thanks for the answer. ... When your new box comes in and you run more tests. Maybe you can compare: beads vs. toroid w/ multiple turns vs. just loops of coax. I'd be very interested in these results. 73
I'd be interested to see a comparison between beads and toroids. For example 2 beads Vs 2 turns through a toroid. 5 beads Vs 5 turns through a toroid etc
how about "ugly balun" coax chokes wrapped around a pic pipe, how do those work and is the effect similar? thx
Yes, my tests showed that they worked great. I hope to demonstrate that in Part 2 and maybe a Part 3. We have kids here from VA and I want to spend some time with them as best I can. I still have to keep away due to my depressed immune system caused by MDS and Neutropenia. 73, Jim
Wow 10? I assume that nearly doubles on 40-80m? Any repercussions to adding too many beads for tx losses? Thanks agn Jim. Been wondering these questions as well. You may need a larger box.
Ya Jay! A bigger box is on the way. More did change the curve and it got a bit weird. So, I hope that the new device will give me better results. Also, a core with coax run in and out several times was the best for bandwidth and results. I will talk about that too when the new device arrives. I am not sure what I bought until it gets here. The manufacturer has not answered my emails. 73, Jim
@@ham-radio I’m not sure what’s going on with manufacturer’s these days. I decided to purchase a “hart” brand string trimmer in October. Well In March the motor went up in smoke. “Electric”. I’ve emailed and called 2 times a week with no response. So much for their taking pride in American made products right.
Good morning Jim, this is Fred. Does it matter If I cut out the plastic and put the ferrites directly on the copper braid shield without the plastic cover?
Why? It won't improve anything.
G54GHB.
HI Jim, do the beads affect TX or RX or both?
Yes, the beads choke stuff on the outside of the coax. That can include somethings that sound like noise. Good question! 73, Jim
Doesn’t the number of beads depend on the frequency ?
Did you try 6 to 9 loops of coax?
That's a different kind of choke and can work if you need such.
There's free noise canceling software floating around there's a couple RUclips videos about it basically you can have air conditioner running in the background or a Shop-Vac and the software stops you from hearing all that they only hear your voice so make me look into that that way you can enjoy your air conditioner while you're making your videos just a friendly heads up
Or get a split unit with a quiet indoor exchanger. Can't wait to get mine running and be RID of that NOISE!
What difference does the ferrite mix make?
It changes their impedance on different frequencies. A good mix for low HF won't be as effective for VHF, ect. So, you may want to be choosy about the mix you use for your application. If you are a single band operator, like a GMRS or CB or a Technician who uses local VHF/UHF LOS, your choice will be simple.
If you run a very large station with many bands, keep in mind that you will be better off having common mode chokes for all the bands you want to quiet down, because RFI will travel down your VHF coax that will get into the shack to interfere with HF, for example.
It would be helpful if you got to the point sooner...no offense Jim.
Let me briefly think about which of these is more important. You running out of time or Jim running out of time? You should be grateful that people put this info up on YT in the first place, because it saves time. Personally, it took me months of research, on and off, to learn this and make effective ferrite chokes for a certain application, including sourcing the right items. Before and after that, years of study on theory and practical to back it up. I was going to share my thoughts on a way to do it better and save money, but you'll have to find that out for yourself now. Happy trails.
You are looking good. I wish ARRL would stop saying Amateur radio is just a hobby. Through the years we have developed so many ways in which we all communicate. I feel that when the powers that be hear that we are only a hobby that more of our frequencies will be taken away. I just can't figure out why they have started to say and print that it is only a hobby. experimentation is what we do. de WB7ORB
Thank you. N0QFT
each bead add .5uH