Coil coax around a ferrite and connect the outer shield for a S21 measurement. Loss in S21 = choking :) typical ferrite for line noise choking is #31 (also for top bands 160m - 80m). #43 does a great all-round job on higher bands. #52 is a newer kid on the block. Higher curie temperature, which translates to higher power rating + it's quite capable on all ham bands. All of this from perspective of an HF ham radio operator ;)
