Coax Common Mode Noise Filter - 500 Watts PEP, 1-60 MHz, -38dB Common Mode Noise Suppression!
Product Details
MPN: CMNF-500-50
Country/Region of Manufacture: United States
Filter Power Rating (PEP watts): 500 SSB (25% duty cycle), 250 Watts CW/FT8 (50% duty cycle)
Choking Impedance (ohms): 1K-14K
Common Mode Attenuation (db): 21-38 db
RFI Suppression Range (MHz): .1-60
Insertion Loss (db): .0092 (1 MHz) - .0396 (50 MHz)
Enclosure Size (inches): 3" x 2 x 1"
Typical Use:: Coax Noise filter at radio end of coax
CMNF-500-50 — Coax Common-Mode Noise Filter (HF, 500 W)
1.8–65 MHz 50 Ω • SO-239 Up to 500 W PEP Typical 4–6 S-units noise cut
What it fixes (in plain English)
Common-mode current rides the outside of your coax braid like a second antenna. The CMNF-500-50 adds high choking impedance on the braid, so neighborhood hash and “mystery” RFI don’t get dragged straight into the receiver.
- Lower S-meter baseline • cleaner waterfall
- Less RF-in-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 station? Use one filter per feed line. Most antenna switches only switch the center pin—the braids stay tied together and share noise.
- Portable: at the radio or station entry point works great.
Which model should I choose?
- Up to 100–500 W PEP: CMNF-500-50 (this page)
- Amplifiers (1.5/5 kW): CMNF-1500HF / CMNF-5000HF
- Low-band focus (0.2–7 MHz / 160 m): CMNF-1500LF / CMNF-5000LF
- 75 Ω TV/CATV: CMNF-500-75 (CMNF-TV)
60-second “Do I need this?” test
- Unplug the 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 (one per feed line).
Manual highlights
- High choking impedance on braid; passes desired signals normally
- Use short jumpers; keep filter near radio/entry
- Best results with one filter per feed line in multi-antenna stations
What’s in the box
- CMNF-500-50 filter (SO-239 both ends)
- Quick-start sheet + placement diagram
| Impedance | 50 Ω |
|---|---|
| Frequency range | 1.8–65 MHz (HF wideband) |
| Power | Up to 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
On Sale
RG-8X Coax Jumper Cable with PL-259's on each end - 3 feet
RG-8X Coax Jumper Cable with PL-259's on each end - 3 feet
SKU RG-8X-3
List price $19.95
Save 25%
$14.95
