120 Ohms at 100 MHz — what that means on the line
The BLM15BB121SH1D is a single-line ferrite bead from Murata's EMIFIL® BLM15 series, in the 0402 (1005 Metric) footprint. Its 120 Ohms impedance at 100 MHz is the peak suppression point for common conducted noise in the 80–200 MHz band — think clock harmonics, switching-regulator edges, or digital bus radiation that couples onto a power or signal trace. Because it is a differential-mode (single-line) filter, it inserts series impedance into one conductor only — no common-mode choke action.
Active production — no lifecycle watch needed
The base product number BLM15BB covers the whole 0402 impedance family; the suffix 121SH1D specifies the 120 Ohm variant and the packaging (Tape & Reel, Cut Tape).