Braid-breaker

The radio frequency (RF) current flowing through the tuner of the TV tends to generate harmonics which then spoil the viewing.

Ferrite ring chokes work by presenting a high impedance to signals traveling along the braid only, but passes through differential-mode ("balanced") currents unchanged.

The wanted signal is in differential mode with an equal and opposite current flowing in the braid to that in the cable core.

The currents from the wanted signal, however, produce equal and opposite magnetic flux in the ferrite which cancel out.

The resistor acts as a “slow leak” on the ground wire that prevents buildup of static electricity on the TV aerial, but is too high a resistance to pass a signal carried along the cable, which operates near 72 Ω.

Homemade 1:1 balun using a ring of ferrite around which the coaxial cable is wrapped. This simple RF choke impedes signals passing on the outside of the braid, which helps to cure television interference .
On the left is a normal TV installation which is being troubled by TVI while on the right is a TV installation which has features to eliminate/mitigate the TVI