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Eliminate both metallic and longitudinal Radio Frequency Interference (RFI) noise

RFI occurs when radio, television, business or citizens band transmitting equipment is located near telephone facilities. Generally this unwanted audio signal is picked up by telephone cable, which acts as an antenna, and the signal is radiated directly into the telephone set.

There are two forms of noise:
  • Longitudinal noise is transmitted down one or more wires in one direction and returns via earth ground
  • Metallic noise is transmitted down one wire and returns on a different wire

Charles offers suppression electronics in three styles. Two designed for indoor use and one for outdoor use. Unlike other capacitive filters, Charles’ eliminates both longitudinal and metallic noise.

RFI Suppression Electronics


Model 12-10A Suppression ElectronicsModel 12-10A is a specially compact network contained in a shrink sleeve that measures approximately 2" long, .75" wide and .50" deep. This compactness allows this network to be installed quickly and easily with a phone set, including some slim sets.

The five individual conductors are color-coded and terminated with spade lugs for easy connections. Use for indoor mounting only.


Model 12-09ALS Suppression ElectronicsModel 12-09ALS has the network contained in a circular ABS housing, 1.3" diameter and .65" deep. All components are completely encapsulated.

The five individual conductors are color-coded and terminated with large spade lugs for easy connection.

Only nonmagnetic hardware can be used if this network is to be secured through the center hole as shown in the installation. This unit is suited for outdoor mounting, such as in a station protector.


Model CS1542A-RFS Suppression ElectronicsModel CS1542A-RFS is a durable, beige-colored plastic housing that measures 2" wide and 4.4" long and 1.2" thick and is installed in series with the telephone line cord. The telephone line cord can be plugged into the female receptacle and the standard 6" insulated lead with the male plug can be inserted in the female wall jack. In the event a wall jack is not present, the inside/outside wire can be hard-wired to the internal screw lugs.

The input modular is pre-wired through the RFS network and may be stored within the housing if hard-wired installation is utilized. Output is achieved through a 4-conductor modular jack receptacle mounted at one end of the housing. Mounting screws are included. Use for indoor mounting only.


Resistance (tip to tip & ring to ring) 9 Ohms (+/- 2 Ohms)
Inductance (tip to tip & ring to ring) 2.2 MH (+/- 5%)
Max. attentuation at voice frequency 0.5 db
Min. attentuation at 300 KHz 37 db
Continuous current rating 90 MA
Intermittent current rating 500 MA
Coupling capacitance, tip to ring 0.005 MFD (+/- 20%)

Ordering Information

Model Description Quantity Application
12-10A RF RFI Suppression 5 Indoor
CS1542A-RFS RFI Suppressor 4 Indoor
12-09ALS RFI Suppression 3 Outdoor

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