Wednesday, June 15, 2016

Common-mode current choke for the RX cables

   I am rebuilding all the RX low band antennas switching and filtering at OL7M. As you can find in a lot of literature - LBDX etc - it is really a good idea to do maximum for suppression of common-mode signals induced on the outside of the feed line:
source: ON4UN's LBDX

   Than I tried to use our ferrite cores. You can find it there: FT-25M533-CTY. So I used a good quality coax cable RG316 and wind it to 4 pieces of that core. As you can see on the pictures:

 There are the cores in original plastic cover - see the measurements

 Example of use in Bi-directiona beverage feeder - see

Common-mode attenuation for 4 cores and 5 turns of RG316
 Common-mode attenuation for 4 cores and 8 turns of RG316
 Common-mode attenuation for 4 cores in the plastic cover and 7 turns of RG316

   And the results? These cores are really suitable for the common-mode chokes! And 4 cores and 5 to 8 turns can by use in really wide frequency range: 160 to 6m. The 8 turns is great on 160m to 20m and fine up to 6m. Less turns improve parameters on higher frequencies.

   If you are interested in that, you can order the cores on the web page.


Kit or assembled CMCC are available at

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