This article describes a common mode choke intended to reduce RF interference with a VDSL service.
The MDF is located where the underground cable enters the building. From here it rises vertically and travels some 25m across the ceiling to the VDSL modem.
The choke can be seen in the pic, it is 7 turns of CAT5 data pair wound around a LF1260 ferrite sleeve.
Above is the measured common mode impedance R,X of the choke. It is designed to peak between 3.5 and 7MHz to afford some moderately high impedance at both frequencies.
Measurements were made with a nanoVNA-H and the graphic made in Python scikit-rf from a saved .s1p file.
On test, the choke is effective on 40m.