Reduce Common Mode Current (CMC) with a Easy to Build Choke

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

FT240-43 Toroids:

Toe-Roid master TheSmokinApe:

⏱️Chapters⏱️
0:00 What is a Common Mode Current Balun
0:57 Steve G3TXQ - Common-mode chokes
4:20 Winding the choke

Buy HRDX Merch:

Items I use in my shack:

HRDX shops at Australia's newest Amateur Radio store Connect VK:

Please consider using the affiliate links to support this channel:

If you enjoyed this video help others enjoy it by adding captions in your language:

#HamRadioDX #CommonModeCurrent #Choke

Fan "Ham" Mail:
PO Box 5071
Sandy Bay, TAS 7109
Australia

Music:

[HamRadioDX]

*Yes I know I said a "common mode current balun"... it's not really a balun, it's just terminology I incorrectly used 👍

[DNLGSA]

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

[Jim.Hummel]

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.

[vkycj]

Nice work Hayden. For better performance on 160m and 80m the Fair-Rite Mix 31 is the ants pants. 73, Jamie VK2YCJ

[jamesacland]

Would love to see a before and after on the air. Thanks Hayden.

[paul_daniels]

Great video for newbies and many others Haydn.

[DonDegidio]

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

[AADX]

Great video Hayden.
For QRO you can use PTFE (inner insulator) coax such as RG142 instead.
73

[VKIM]

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

[VKMUD]

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

[uvxecqy]

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.

[mikenyo]

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 ;)

[truckinghamkdok]

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.

[russ_vee_jr]

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.

[rallypoint]

Easy vid!!! Steve (silent key-RIP) has an updated chart on the site. Right below the main chart. Good stuff though!!

[AdamSWL]

Great idea to use a cable tie.
You avoid roid rage by not having the cable come loose as you wind it!

[pauls]

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.

[battlestarone]

Thought it was best to place a choke before coax enters the shack not at antenna end, , , is rhis up for debate

[mikesradiorepair]

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

[aarongriffin]

Can anyone explain what the waterproof box is for? Is the toroid not able to be in the weather?