When using long wire antennas or any antenna that is not a perfect VSWR of 1:1 you will have RF power returning back up your feeder cable, potentially into your radio equipment.
An RF Choke or 1:1 Line Isolator, as they are sometimes called, can help prevent the outer of the coax from radiating RF and reduce the amount of reflected RF reaching your radio.
They can also be placed near your ATU/Radio to help reduce noise pick-up from your feeder coax cable.
Available in various models:
HTRFC100 – Uses an FT140-43 rated at 100w across 7-28MHz
HTRFC400 – Uses an FT240-43 rated 400w across 7-28MHZ
HTRFC400L – Uses an FT240-31 rated 400w across 3.5 – 28MHz
SO239 connectors provided for Radio and Antenna connections.
I ONLY use high quality branded (Fair-Rite) ferrites in my range of Baluns and UnUn’s which does increase the cost, but when you can spend £100’s or £1,000’s I wouldn’t want to save £10 on a non-rated Chinese fake piece of protection equipment attached to my radio.