[RFI] Common mode choke on 4 Square feedlines without skewing phasing?

[Andy KU7T]

Hi,

I am constructing an 80m 4 Square using DXE phasing unit. The instructions clearly say to not add any matching components or decoupling devices like baluns or coils between the phasing unit and the verticals.

I am using 4 elevated radials at about 9 feet height (I would rather not debate that decision further…). It is usually suggested to use a common mode choke on any antenna feed point, especially for elevated radials.  Adding an conventional choke would likely change my phasing.

So, I am looking for more information about making a current choke that does not change the electrical length of the phasing coax cables. Is making a stack of a few ferrite cores right on the feedline (maybe with a few coils if I have the length available) ok to do?

I have read http://www.nu9n.com/images/RFI-Ham.pdf, and current chokes are extensively discussed there. My question is whether winding on the phasing coax or sliding over the coax will change phasing or not. I am thinking it does not, but wanted to check here…

73
Andy
KU7T




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