Coax Common Mode Noise Filter - 500 Watts PEP, 100 KHz-30 MHz LF & BCB up to -46db Noise Reduction
Product Details
MPN: CMNF-500-50LF
Country/Region of Manufacture: United States
Filter Power Rating (PEP watts): 500
Choking Impedance (ohms): 1K-14K
Common Mode Attenuation (db): 21-46 db
RFI Suppression Range (MHz): .1-30
Insertion Loss (db): .0092 (1 MHz) - .04 (30 MHz)
# Ferrite Filters: 1
Enclosure Size (inches): 3" x 2 x 1"
Typical Use:: Coax Noise filter at radio end of coax
CMNF-500-50LF — Coax Common-Mode Noise Filter (HF, 500 W)
100 KHz-30 MHz 50 Ω • SO-239 Up to 500 W PEP Typical 4–7 S-unit noise cut
What it fixes (in plain English)
Noise rides the outside of your coax braid like a second antenna. This filter blocks that common-mode current so the radio hears less neighborhood hash and fewer “mystery” RFI paths—without touching your antenna.
- Lower S-meter baseline, cleaner waterfall
- Less RF in the shack (mic bite, router resets, audio buzz)
- Stabilizes multi-antenna stations where braids get paralleled by switches
Where to place it
- At the radio end of each coax run, before any switch/splitter/amp.
- Multi-antenna? Use one filter per feed line. Most switches only switch the center pin; braids remain tied together.
- Portable ops: put it at the radio or at the entry point to the station.
Which model should I choose?
- Up to 100–500 W PEP: CMNF-500-50LF (this page)
- Low-band focus (0.2–30 MHz / 160 m): CMNF-1500LF / 5000LF
- 75 Ω TV/CATV: CMNF-500-75
60-second “Do I need this?” test
- Unplug coax; note baseline noise.
- Touch the center pin only to the radio jack—note noise.
- Touch the shell only. If noise jumps, your braid is carrying noise → a CMNF will help.
Manual highlights
- High choking impedance on braid; negligible effect on desired signals
- Use short jumpers; keep filter near radio/entry
- For best results on multiple antennas: one per line
What’s in the box
- CMNF-500-50LF filter (SO-239)
- Quick-start sheet + placement diagram
| Impedance | 50 Ω |
|---|---|
| Frequency range | .1-30 MHz (LF + HF wide band) |
| Power | 500 W PEP (SSB). Reduce for high-duty digital/CW. |
| Connectors | SO-239 (UHF female) both ends |
| Placement | At radio/entry; one per feed line in multi-antenna stations |
Duty-cycle reminder: Ratings are SSB PEP. For continuous digital (FT8, RTTY) or long key-down, use lower power or a higher-rated model.
Multi-antenna Station Bundle (500 W)
- 2× CMNF-500-50 + two 3-ft RG-8X jumpers
- Add a third unit if you use a separate receive antenna or second HF line
