Reduce Common Mode Current (CMC) with a Easy to Build Choke
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- Опубліковано 8 лип 2024
- Common Mode Current can really mess with RFI and cause interference in the shack. In addition, you could also be receiving unwanted interference on the coax outer shield.
In this video I show how I built myself an easy CMC choke using a toroid and RG-58 coax.
Amateur Radio (G3TXQ) - Common-mode chokes
www.karinya.net/g3txq/chokes/
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⏱️Chapters⏱️
0:00 What is a Common Mode Current Balun
0:57 Steve G3TXQ - Common-mode chokes
4:20 Winding the choke
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*Yes I know I said a "common mode current balun"... it's not really a balun, it's just terminology I incorrectly used 👍
*Best Ape voice*
That's TOE ROID, son!
@Lionel L. KJ7OH Never thought I would do a video about roids 😂
@@HamRadioDX hemorrhoids 🤣🤣
UA-cam hams far too misinformed than you would think. They always hide beind " misspoke"
Thanks for your clear, concise explanation on this...especially the reference sheet as I found it overwhelming when I first learned about these. I'm really enjoying your content.
Glad it was helpful thanks for the comment Jim!
Hayden, thanks for the build vid. Certainly will be making one of these. I like the fact that you've put yours in the waterproof box! Cheers and 73
No problem 👍
Great video for newbies and many others Haydn.
Thanks Paul, hope things are well down there. Looking forward to meeting you in person on your return trip
Great video Hayden.
For QRO you can use PTFE (inner insulator) coax such as RG142 instead.
73
Very informative, thank you!
I pretty much have one of these in line on my 30' lmr-240 coax I use on POTA. Props to you for using zip ties, I was too lazy to even do that. Still works great ;)
Haha thanks Mike.
great video, thanks!
Nice work Hayden. For better performance on 160m and 80m the Fair-Rite Mix 31 is the ants pants. 73, Jamie VK2YCJ
I love this video.
You're a legend JoeBrett, thanks man
Hi Hayden,
Nice build. There is a satisfaction in making something with your own hands. For more power handling a direct replacement for RG58 would be RG400, and stacking the toroids in combination with the RG400 would handle 1KW. For about 100W, RG316 would be a nice small diameter coax, but RG58 would also be sufficient at that power level. You and the family stay safe. 73 WJ3U
Thanks for the tips Don. Yes for my application RG58 works just fine as I won't be running more than 100W, but great suggestion about RG400 and 316 for the lower power too. 73
I swear that you've been looking over my shoulder, I made mine the other day and used the same resources as you, just waiting for some more spare time to solder it all together and put together my DX Commander Classic and hopefully I'll be putting out a better signal than my inverted V. Also I sit for my standard exam on Saturday, seven weeks after receiving my foundation licence. You might say I'm keen. 73's Hayden. VK4MUD
Congratulations John! Good luck on the Standard licence, I'm sure you'll pass with flying colours. Be sure to let us know how you get on. Haha! I had some other ferrite used as a CMC but I don't think they were as effective as the FT240-43. Hopefully this week I will get the DXC up myself, I've been very slack!
Nice build.
Thanks!
the air cored are capacitive and used with a ferrite toroid (inductive) of correct mix and turns, one can actually create a tuned circuit of desired freq. Have fun.
G3TXQ's updated web-page chart shows that 9 turns of RG58 on 3 stacked 240-53 cores provides more than 8K of impedance from 40M through 10M.
That's what I'm using at the output of my my SWR Meter to my 40M EFHW Inverted ELL on 45 feet of LMR400 with a 51:1 Transformer.
Got rid of most of my local 0:00 interference into my TS590SG.
Thanks for the shout Hayden 👍
Thanks for watching Ape, king of the toe-roid
@@HamRadioDX lol
RFI is a good point at any time
Would love to see a before and after on the air. Thanks Hayden.
Thanks James, I've still got the antenna to go up. It's nice weather today, so hopefully if I get home in time I might be able to do that. 73
Nice job Hayden. I wonder, when used with a 100w txcvr, how would you see any difference? Better match? How does less RF returning down the coax manifest?
Yes plz
Interestingly. I've made the same choke BUT I did not stick it in a box. Just a male PL259 line socket on one end and a female on the other (SO239 line socket). Water proofed with glued heat shrink and self amalgamating tape. I figure the coax is waterproof anyway, so the box is a bit of work I can do without. Been using it (them) on my vertical and Moxon with no ill affect. Cheers Adam
Thanks Adam, I probably could do without the box but eh it looks good
Thank you for posting this video instructions. The flux lines induced by the current flow in each winding all add up in the toroid, and not cancel out :so kindly correct me if I am wrong?
It might be interesting to include 2 tests of your handiwork to see how effective this balun is. Test for SWR and Common Mode Reject.
Great idea to use a cable tie.
You avoid roid rage by not having the cable come loose as you wind it!
Roid rage sounds like something completely different 😂😂
Easy vid!!! Steve (silent key-RIP) has an updated chart on the site. Right below the main chart. Good stuff though!!
Thanks mate, glad you enjoyed it
Can anyone explain what the waterproof box is for? Is the toroid not able to be in the weather?
With the comments about maximum bend radius stuff… can it be wound looser or do they need to be wound tight around the torroid? Cheers and thanks from gary
It posible for 3phasa sir?
Thanks, I generally thread the end of the coax through the hole rather than forcing the bend (bight) through as it seems to reduce stress on the insulation of the coax around the core which is sometimes foam.
Thanks, great tip!
@@HamRadioDX No worries, great channel and don’t forget to turn those 2m SSB beams across Bass Strait from time to time....
Is it better to use coax to wrap it around ferrite core or can I use regular (antenna) wire?
Thanks Hayden. Did you try this on 6m?
i use 43 mix for mine and i use two of them ferrites with 13 turns seems to work good 73 from m7byf
Can you do a video with the rg213
Hi where can i get theses for the rg213 and rg58
Good video and tnx. Mix 31 will give better performance on HF, and the bible for CMCs is the K9YC Common Mode Choke Cook Book available $FOC online. Jim's work is legendary.
Thanks for the info!
Thank you for sharing , will this choke work on 27 MHz ?.
What co-ax did you use?? I have some leftover RG213 feedline. If I have used RG213 as my antenna feedline can I use RG58 for my CMC Balun?? I only run about 60-100w depending which mode I am running.
Yep that will be fine.
Nice one Hayden, that site is a great reference. Where did you get the box from? been looking for one like that! Cheers Tim VK5AV
The box came from Jaycar, let me find a link....
IP65, so dust and hose proof. I don't think it will be submerged anytime soon ;)
www.jaycar.com.au/ip65-sealed-polycarbonate-enclosure-with-mounting-flange-115-w-x-65-d-x-40-h-mm/p/HB6249?pos=8&queryId=268d02a9b2368dde57e21b774560e248&sort=relevance
How much RG58 makes 17T around FT240-43?
would snap on ferrite beads work better with less loss, since you would not be cutting the coax and maybe using less quality coax in the feed line?
mix ix less forgiving with snap-on roids. snap on require smaller dia. to get same number of turns (larger loss). ideally slide on 25 or so with correct I.D. to fit (then use heat shrink to keep together) then terminate the ends. snap-on are typically used on dc power cords to suppress noise from supply.
Hello. Nice build. On the website there is a summary chart, and further down there are 3 different charts for each torroid mix. There is a difference between the same configuration on the summary chart and individual one. For example, if you compare 12T RG58 on FT240-43 on the summary and individual (43mix) charts, the graph bars are very different. What chart is correct?
The summary chart is dated May 2012 and the Type #43 chart is dated December 2017.
"Since making measurements for the original chart (above) I have made further measurements on combinations of 5 turns, 9 turns, 12 turns and 17 turns on single, 2-stacked and 4-stacked, #31, #43, #52 and #61 "240-size" toroids. The results can be seen here".
I guess he got different results due to testing methods that he refined over the few years between. I've always references the latter charts.
@HamRadioDX Thank you for confirmation! It seems 12T on FT240-43 gives really good results on his setup.
Hi. I built a copy of your current mode choke which appears to work well. One immediate effect was when I put my hand on the metal case of my Xiegu G90 the noise level jumped up very noticeably. With the choke, this effect has completely gone 😀
Silly question. Why do most chokes (and baluns) like this one cross the coax over to the other side and wind in the opposite direction? Is this something to do with phase cancellation or just a convenient way to enable the coax ends to come out at opposite sides for connection.?
73s ROB VK5KRM
Hey Rob,
Just a convenient way for the coax, or windings to come out the opposite sides for connections. The crossover also counts as a turn through the core too. Cheers Rob!
Thanks Hayden. As I suspected. I have seen chokes without the crossover as well as the air core ones. 😀
73s @@HamRadioDX
Might help when they drop the EMP. 🤔
I'm guessing this would be connected directly to the tranceiver end?
edit: I just rewatched the video and you said antenna end.
Antenna end 👍
will adding ferrites ( 5 or more ) along the coax do the same thing as an choke?
It won't be as effective as winding multiple turns through. But you will get some choking depending on the ferrite material and core type.
Hayden- does this create any “issue” if my primary feedline is LMR400? Bigger pipe going into smaller pipe, as it were…?
LMR400 is pretty rigid feedline, you won't be able to pass multiple turns through a core this size. Best to use clamp type toroids (although you'd need a lot to be as effective as multiple turns) or wind this with some RG-58 and stick it inline with your LMR400 at the antenna feedpoint.
@@HamRadioDX I may not have been real clear on my description. Obviously can’t wrap LMR… the LMR would go in 1 side of the Chile but the end that connects to the antenna would be only the rg58.
@@HowToHam_Tom Yeah that will work fine. Just put the RG-58 toroid close to the antenna feedpoint
Where did you purchase the plastic weather-proof box (and part number)? TIA.
Jaycar Electronics in Australia:
CAT.NO: HB6224 or something like that (I'm not sure if that is the correct size)
@@HamRadioDX Thanks.
Could you use more than one that covers different bands ?
Yes you can by having two on the coax line
It looks like you have 13 turns through the toroid core, not 12. A turn is not a full wrap around it, it's a pass through the center. I am counting 13 passes through the center. Could be mistaken but that's what it looks like to me. KC3OSD Mike
Good eye! I picked this up after I recounted and stopped the video. At 6:34 I mention this, the cable tie looks like a turn too I've noticed!
Hi good morning from the UK, and thank you for your great video's , I have started making the Choke, but the question I have is that I am using an " End Fed Half wave antenna" with a 49:1 balun fitted, my question is where should the choke be fitted, having been to several sites on the net, some say "do not fit near the feed point" other say "fit it 1 to 3 feet away" and others say fit it where it enters the shack" your thoughts would be much appreciated ? best regards Alan
Hi Alan,
The CMC balun can be placed on a EFHW antenna at a length of 0.05 wavelength of the lowest frequency required. So for 80m it can be placed 4 metres down the coax. This is due to if you place it any closer it may mess with the counterpoise length - of course this may vary if you use another counterpoise.
www.aa5tb.com/efha.html
@@HamRadioDX Hi Hayden, thanks for the reply, would there be any benefit fitting it at the entry point into the shack, I guess the answer to that is try it and see ? 👍 thanks again
You could possibly try two? If you put it near the entry point to the shack, just remember that the rest of the coax to the antenna could potentially have CMC on it, or pickup common mode noise too. Cheers
@@HamRadioDX Ok thank you..
But the best thing to do is experiment! Good luck Alan!
Thought it was best to place a choke before coax enters the shack not at antenna end,,,is rhis up for debate
I tried a coax choke... it got quite but. My swr went up
Just wondering why you use an enclosure? The core is non-conductive and the coax is weatherproof.
Because I'm pedantic I guess? It will look good sitting out on the lawn
What toriod would i need for rg213 and how many turns for the 213 and for rg58 ? And can you get back to me please
RG213 might be a bit thick to wrap around a toroid. In the description there is a link to Steve's website detailing the turns for RG-58. For 213 you may have success with slipping on multiple ferrite beads onto the coax line, but you may need to do some research on what mix is the best. TheSmokinApe may of done a video on it
@@HamRadioDX ok cool thanks
Would like to have seen performance.
Future video my friend
You actually had 13 turns, but who is counting (besides me). I do the same thing when passing coax through the toriod. I end up with either 11 or 13 turns as much as I try to get 12. But +/- 1 turn does not make a major difference. Well done on the video.
He pointed out and corrected that right before he cut off the second cable tie.
He did fix it back to 12 turns but what would be the effect if he left 13 turns? It has diminishing return after so many turns but not to a negative affect, right? Why correct it if 13 turns fit? @@RC21114
no wonder that this will function as a choke if you consider the minimum bend radius of rg58u (Min. Buigradius( in), 2")
thank god someone else has the common sense to comment on this. I just did the same. It's obviously unacceptable.
Need one for 27mhz
I made one for 11m out of 3’ of RF-58a/u using a mix 61 toroid. 12 turns works amazing for that band. Actually mix 61 worked better than 31 and 43.
Not disagreeing at all since it works but I am having trouble reconciling the usual construction methods of a torroid based filter with the minimum allowable bend radius of the coax, especially at power. I was taught never to exceed the minimum bend radius which this construction method certainly does. Can anyone help set me straight?
An interesting question, one that I probably cannot answer correctly.
There a lot of coax choke "flowerpot" antennas here that use similar or smaller bend radius, especially the VHF ones.
vk2zoi.com/articles/half-wave-flower-pot/
That's a toe-roid ya know ;)
I did refer to it as that at one stage 😃
Easy As
Easy Az bro. ua-cam.com/video/4Sw6YJOcVWk/v-deo.html
@@HamRadioDX That's a nice deck!
You watch it just for that
why 43 ??? you are doing it for hexbeam so 14-50 MHz material should be 61
No this is for my HF antenna covering 80m-10m
Does steve have facebook
13 turns there not 12
Why is it common practice to totally disregard the minimum bend radius of the coax? You've far exceeded it here. Put it this way, would you otherwise accept a coil in your RG58 feedline almost as tight as the curly cord on a microphone? Hams are so dumb.
How else ya gonna wrap it bud? You got a toroidal core that's big enough you won't exceed the bend radius In yer pocket? It's clearly fine, one and done. Wouldn't recommend you go wrapping and unwrapping and rewrapping the same coax over and over. However as a one time wrapped permanent installed coax it's been proven to be fine. But hey let us know this better CMC you've got up yer sleeve with readily available parts many already have laying around, we're all ears friend.
@@MarkoManiac bud, it far exceeds the minimum bend radius, by a mile. You have proof it doesn't matter? Then why would the manufacturer specify it?
My ferrite chokes are very substantial and properly designed for the frequency of use. I loop them so as not to exceed the minimum bend radius and space the loops out evenly to avoid any unwanted stray capacitance. In fact, I use 5 stacked FT240-43s for each choke. Sound good enough to you, bud? Do you need anymore solid, technical advice?
@arconeagain Naw. Don't need solid "technical advise" that isn't anything of the sort from a sad ham.
😊 Is this the winding you use for the 1/2 Vertical? 😮 FOO somewhere in ROK 🇰🇷🇦🇺 an Alien in Asia 👾
@@vk4foo ?