Palomar CMNF-500-50 User manual

COAX COMMON MODE
NOISE FILTERS,
MINI-CHOKER, MINI BALUN
PRODUCT MANUAL
© Palomar Engineers, Inc., 1965-2020
Palomar-Engineers.com
Coax Common Mode Noise Filter/Mini-Balun Models
Model #
Range
(MHz)
PEP
(ICAS)
CMRR
Size/notes
CMNF-500-50
MC-1-500
1.8-65
500
20-38
dB
3” x 2” x 1”, SO-239 I/O
MB-1-500-50
1.8-65
MHz
500
20-38
dB
3” x 2” x 1”, SO-239 In,
Balanced output
CMNF-500-75 or
CMNF-TV
1.8-65
500
20-38
dB
3” x 2” x 1” ”, “F” connector
I/O
CMNF-500-VHF
15-180
250
20-30
dB
3” x 2” x 1” ”, SO-239 I/O
CMNF-1500HF
1.8-65
1500
20-38
dB
4” x 4” x 2” ”, SO-239 I/O
CMNF-5000HF
1.8-65
5000
20-38
dB
4” x 4” x 2” ”, SO-239 I/O

© Palomar Engineers, Inc., 1965-2020
Palomar-Engineers.com
The Problem:
Common mode current induced by radiated sources (plasma TV, routers, computers, transmitters, etc.) can be
picked up by the outside of the coax braid from the antenna feed point back to the receiver. This portion of the
coax braid acts like a second receiving antenna, picking up common mode noise signals that combine with weak
signals (traveling down the center conductor and inside of the coax braid) making it difficult or impossible to
hear weak signals! See diagram below.
The Solution:
A coax common mode noise filter with high choking impedance at the receiver/transceiver end of the coax
effectively reduces common mode noise present on the coax braid while passing desired signals present on the
coax center conductor. For best results, and to reduce co-interference between choked and un-choked feed lines
with multiple antennas, EACH antenna feed line entering the radio room needs to have a coax noise filter even
if it feeds a common coax switch since most antenna switches ONLY switch the center conductor of the coax
line, yet all the coax braids are ALWAYS connected together in parallel. So when an antenna is NOT
SELECTED, its coax sheath still contributes to the noise level of the connected antenna through the common
connector ground!
Example installation of CMNF-500-50 on an Icom 756 Pro III with two antenna
inputs and using the internal antenna switch. Each coax shield is isolated from
the other by the common mode filter. Coax braid common mode current are
effectively stopped before
they can combine at the
coax connector.
A similar installation can be
used with a multi-antenna
switch but using short coax
jumper from the CMNF-500-50’s to the antenna switch.

© Palomar Engineers, Inc., 1965-2020
Palomar-Engineers.com
Mini Balun/Ladder Line Interface
- MB-1-500-50 uses proprietary Multi-Mix, Multi-Core, Multi-Turn ferrite
technology for maximum choking (up to -38 dB common mode noise
rejection) and maximum bandwidth
- 500 Watts PEP, 50 ohm SO-239 connectors Input and Balanced Output, 1-61
MHz (usable to 100 MHz), 1:1 balun included
- Works for all ladder line antennas from 1.8-61 MHz (160-6 meters) -
excellent for G5RV/ZS6BKW, OCF flagpole antennas, ladder line to remote
antenna interface..
- 2-5 times more common mode noise rejection, wider bandwidth and higher power then competing
isolators
Noise Filter Installation and Use
The CMNF-500-50 is designed to be placed in a 50 ohm coax line entering the transceiver (or between the
transceiver and amplifier). The CMNF-1500 (1500 watts PEP) or CMNF-5000 (5KW PEP) should be placed at
the end of the coax into the station before any antenna switches. All CMNF’s have high choking impedance
over a very broadband frequency range and are very useful for high bandwidth SDR receivers and general
coverage/ham transceivers from 160 to 6 meters. Typical common mode noise rejection is 30-40 dB (4-7 “S”
units). Either connector can be input or output.
Installation Note: Just as the CMNF’s reduce RECEIVE noise picked up on the coax braid by electrically
isolating the receive signals on the external coax braid between the receiver and antenna feed point, a proper
feed line choke at the antenna feed point will isolate the coax braid from the antenna on TRANSMIT. In other
words, it will prevent your dipole from becoming a tripole using the coax braid as part of the antenna. An
excellent feed line choke is the Palomar Engineers Maxi-Choker™, model MC-1-3000 (3KW PEP rated from
1-61 MHz) or the Mini-Choker™ (500 watts) shown below:.

© Palomar Engineers, Inc., 1965-2020
Palomar-Engineers.com
MC-1-3000 (3KW) Maxi-Choker™ - shown with
optional ground, static bleeder installed
MC-1-500 (500 watts) Mini-Choker™ - Same specs
as CMNF-500-50
Measured common mode noise rejection for CMNF’s and MB-1-500 Mini-Balun –typical up to -
38dB!
CMNF-500-50

© Palomar Engineers, Inc., 1965-2020
Palomar-Engineers.com
CMNF-1500HF
CMNF-5000HF
Revision 2/9/2020

© Palomar Engineers, Inc., 1965-2020
Palomar-Engineers.com
Do you have common mode noise on your coax?
Make this simple test to find out.
1. Remove the coax connector and measure the noise level.
2. Now insert the coax connector CENTER CONDUCTOR ONLY into the SO-239 antenna input
and measure the noise level (it should be higher and include possible signals)
3. Now connect the OUTER SHELL of the coax connector to the antenna input and measure the
noise level. If it is higher you have common mode noise and the common mode noise filter will
help suppress this noise which is carried on the outside of the coax braid (acting as a second
receive antenna).
Common mode noise suppression with the CMNF series of filters is typically 25-36 dB which is
equivalent to 4-6 “S” units on radios with 6 dB/”S” unit or may be more on radios with 3dB/”S” unit.
Check www.Palomar-Engineers.com for latest product updates.