CMC-RF isolators

These are our Common Mode Chokes (CMC) — also called line isolators, current baluns, or RFI eliminators — for antenna systems from 1.8 to 54 MHz. Every unit is designed and measured for maximum resistive choking impedance across its band using our Multi-Zs™ technology, the key to stopping common-mode current on the coax shield that causes RFI, noise pickup, and “RF in the shack.”

Which choke do you need? For most HF antennas, the broadband CMC-130-3K (1–30 MHz) is the workhorse — install it where the coax enters your home. Need 6m too? The CMC-154-3K and compact CMC-154S-3K cover 1–54 MHz. For high-power stations, the CMC-330-5K handles 5kW. Working the low bands, 160m through 30m, the CMC-0510-R is purpose-tuned for 0.5–10 MHz, and VHF operators have the CMC-VHF-2K. On a budget, our snap-on RFI-Kits address lighter cases of feedline noise.

Not sure whether you need a choke, or where it belongs in your system? A choke goes at the point where the coax enters the home — not at the radio, and not at the antenna. Read the full explanation in About CMC, written by Danny Horvat, E73M/N4EXA, who designs and measures every choke on this page.