Ok this is what my buddy says.
The cable that goes from phone to router, loop it, dont just bundle it up, do proper loops as any distortion in the cable can undo the work of the filters, you then take 1 filter and then put the loops threw it, the loop should contain a few wires, as everyloop you do will add another length of wire that the filter has to go over.
basically like say you do 3 loops, it would look like O O O close together, so the filter will have 3 wires going threw the centre of it. IT HAS TO BE LOOPS he says, if you ZIGZAG Bundle the cable then the info isnt going in one direction and can nullify the filters work.
He doesnt have snr values of before and after, but he says, his connection was always 19.100-200 without the filter, with the filter he gets 19.500 and at times 20mbit.
As I say he isnt the retarded kind to make this stuff up, he used to work as a Network engineer but is now onto making machines that make cpu's, so I guess he knows wtf he is talking about.
Whether it works for anyone else is unknown to me, as I havent tried it and thus I cannot say that it does or doesnt work, but there ya go.
I hope this helps.
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[slight edit by mod]