Coax Common Mode Noise Filter - 500 Watts, .1-150 MHz
For coax feed lines with receive and transmit signals, you will love the small size, wide frequency range and excellent attenuation of common mode noise interference
- Reduces broadband common mode receiver noise* picked up on the outside of the antenna coax feed line.
- Wide frequency range works on all brands of radios and coax fed antennas from 1-150 MHz
- Common mode noise rejection up to 21-36 DB (3-6 "S" units) depending on frequency
- Simple plug & play installation: plug a short jumper from the CMNF-500HF to your
radio and plug the feed line into the other SO-239 CMNF-500HF input. Either
connector can be input or output. Rated at 500 watts PEP.
- will work with Bias-T antenna switches and will pass DC voltage from input to output with no attenuation
* not effective for noise from AC power lines or noise received directly by antenna
Choose SO-239 or BNC input/output connectors
Installation Note: For best results, and to reduce co-interference between choked and unchoked coax feed lines with multiple antennas, ALL antenna feed lines entering the radio room need to have a separate feed line choke particularly if they are at a different frequency then HF, like VHF or UHF.
If you use a antenna switch for multiple antennas in the 1-61 MHz range, place the CMNF-500HF in the "common" line of the antenna coax
switch and the receiver.
If you use a higher powered transceiver over 500 watts PEP or use an amplifier, consider the CMNF-1500HF (1.5KW PEP) or CMNF-5000HF (5KW PEP) placed at the output of the amplifier.
This product was formally named CMNF-1/1M prior to October 31, 2017
Application Note: For coax lines with receive and transmit signals, we suggest the CMNF-1 or CMNF-2 with SO-239 connectors in and out which are connected in series with the coax feed line to the receiver/transceiver effectively reducing common mode noise existing on the coax. For best results, and to reduce co-interference between choked and unchoked feed lines with multiple antennas, ALL antenna feed lines entering the radio room need to have a feed line choke particularly if they all feed a common coax switch. Choking only 1 line if you have 5 antenna coax feeds will do little good – you need to choke all five – use the feed line chokes for the individual feed lines and the CMNF between the antenna coax switch and the receiver. All CMNF models are SO-239 input and output. Adapters are available for converting to “F”, or “N” connectors.
The CMNF-1 is meant to be placed in the coax line entering the transceiver or receiver (between the transceiver and amplifier or antenna tuner/coax switch if used). The CMNF-1 has a high choking impedance from 1-60 MHz with higher choking on the lower frequencies where noise is usually a larger problem then on higher frequencies. Convenient SO-239 input and output connectors all easy insert in series in your coax feed line. Use a short jumper from the CMNF-1 to your radio and plug the feed line into the other SO-239 CMNF-1 input. Either connector can be input or output. Rated at 500 watts PEP – if you have a higher powered transceiver, consider the CMNF-2 or CMNF-3. Note that the CMNF’s work best closest to the receiver.
Installation Note: Putting a CMNF at the output of your antenna tuner lessens the choking effectiveness since the impedance may be much higher or lower than the 50 ohm design impedance of the noise filter. The best place to install the CMNF is between the antenna tuner/linear (high power CMNF-2 or CMNF-3) or closest to the receiver/transceiver (CMNF-1). See diagram below. Use sleeve or CUBE™ feed line chokes at the antenna feed point and radio end of the coax to reduce RFI and common mode noise.
Typical user comment:
The filter was quite effective. Was surprised that it actually reduced the noise level more than the signal so S+N/N improved by 1.9 S units. Bill