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

[Dave Cole (NK7Z)]

Hi Andy,

Great choice to use elevated verticals!  See Rudy Severn's info on why at:
https://rudys.typepad.com/files/elevated-ground-systems-article-final-version.pdf

If you are using the DX Engineering box shown at:
https://static.dxengineering.com/global/images/instructions/dxe-tfs4-80b-p.pdf

Why not add the ferrite material on the feedline to the rig, (as it 
leaves the control box), and not the individual verticals?

Also if it were me, I'd bury the individual element feedlines as well as 
the main feedline, to help reduce the RF pickup.  I am guessing that 
burying the coax won't mess with phasing, as long as you keep things 
symmetrical.  I am pretty sure it won't, as Rudy is using buried 
feedline on his 160, 4 square.

Maybe someone can confirm or deny this on the list please?

73s and thanks,
Dave (NK7Z)
https://www.nk7z.net
Award Manager, 30MDG Grid Contest
ARRL Technical Specialist
ARRL Volunteer Examiner
ARRL OOC for Oregon

On 1/22/19 10:50 PM, Andy KU7T wrote:
> 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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> 
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