(Common Mode Current Chokes)
Unwanted RF in the shack due to Common Mode Current (CMC) on the coax can be nasty. Besides burning your fingers on the key or lips on the mic, it can also cause some devices to fault. Worst case it can cause TVI or BCI, etc.
To help reduce CMC on the coax, and RF choke (or CMC Choke) can be placed at the antenna feedpoint. It may also be desirable to place a second one just before the coax enters the house.
There are several ways to accomplish this. I will not try to explain the theory here. I will just show you how I tackle the problem.