It is used to reduce the common mode current which sometimes flows in
coaxial and balanced-pair lines.

It is not a transformer. The 1-to-1 is meaningless. It is just a pair
of wires wound together, as one wire, on a ferrite core. Or in your
case a number of ferrite slugs or rings are placed over a coax line.

In brief, it is just a choke.
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Reg.