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Ethernet EMI Filters

10/100 and Gigabit Ethernet EMI Filters
The DJM Electronics FOIL™ brand Ethernet filters utilize patented technology and are the only EMI/RFI filters for Ethernet on the market that offer 100dB performance from 10kHz to 10GHz and higher. Housed in a single, convenient filter package, FOIL™ Ethernet Filters are the easiest and most reliable solution for bringing 10/100 and Gigabit Ethernet access to all varieties of shielded rooms and enclosures.

Standard signal line filters rely on capacitors and inductors to eliminate unwanted RF signals. However, these types of filters often eliminate the high frequencies that make up the sharp edges of high speed digital square wave signals thereby degrading the integrity of the signal. In order to avoid this side effect, it is necessary for standard signal line filters to have extended passbands that allow the higher frequencies to pass unimpeded. Even the best standard signal line filters offer only 70dB from 50MHz to 10GHz and will only work with 10Base-T. There are no Fast Ethernet (100Base-TX) or Gigabit Ethernet (1000Base-T) standard signal line filters available on the market. Also, it is important to note that standard signal line filters do not differentiate between Ethernet signals and undesirable signals. They act like a "hole" in the shielded enclosure to all signals - good and bad - within the passband.

Unlike standard signal line filters, FOIL™ Ethernet Filters utilize a fiber optic isolation link (FOIL) to maintain 100dB shielding integrity. The filter converts ONLY Ethernet packets, so there is no passband and no transmission of unwanted signals.

We guarantee that FOIL™ Ethernet Filters will not interfere with your network, increase hop counts or degrade network performance - a common problem with standard signal line filters.


FOIL™ Ethernet Filters come in five models:
  • FOIL 10/100v3
    Is a Special Order Only model that is designed for use with 10/100 Ethernet networks.

  • GigaFOILv3
    Designed for use with Gigabit and 10/100 Ethernet networks. The filter will automatically select the fastest communication speed and can translate between 10/100 and Gigabit networks.

  • GigaFOILv3 - POE
    A variation of the GigaFOILv3 that provides Power Over Ethernet (POE) in compliance with IEEE 802.3at-2009. The filter acts as an injector (aka Power Sourcing Equipment or PSE) and does not require POE at the filter input.
    Click Here for More Information.

  • GigaFOILv3 - PLENUM
    A variation of the GigaFOILv3 that is designed to meet stricter safety standards for use in air handling/plenum areas. The GigaFOILv3 - PLENUM must be hardwired to building AC power.
    Click Here for More Information.

  • GigaFOILv3 - EMP
    The only 100dB Ethernet filter that is protected against High Altitude Electromagnetic Pulses (HEMP) and lightning threats.
    Click Here for More Information.


Military Ethernet Filter
FOIL 10/100v3 with modified penetration
and bayonet power connector
FOIL™ brand Ethernet filters can be modified to meet specific customer requirements. If you need an Ethernet filter for a military or harsh environment or require customized housings or functions, please contact us to discuss your application.

Typical Performance
(all models)

Ethernet EMI Filter Under Test

Shielding Effectiveness

100dB from 10kHz to 10GHz

Insertion Loss*

100dB from 10kHz to 10GHz

Radiated Emissions*

FOIL™ Ethernet filters are active filters and produce a limited amount of radiated emissions inside the shielded enclosure. Please contact DJM Electronics for information regarding your particular application.

Insertion Loss performance is extrapolated from tests performed using a method as close to MIL-STD-220B as possible. The nature of twisted pair cabling and RJ-45 connectors makes testing to this standard extremely difficult.

Radiated emissions tests were performed using a method as close to CISPR22 and FCC Part 15 as possible. The nature of the filter required it be mounted in a shielded room and tested from 3 meters away instead of on a standard OATS. Actual emissions performance may differ from filter to filter.

(models as specified)


Certified to UL 60950-1 and CSA C22.2 No. 60950-1
(GigaFOILv3 and GigaFOILv3 - PLENUM only)

Environmental (FOIL 10/100v3)

  • Operating Temperature: 0C - 55C (32F - 131F)
  • Humidity: 5% - 90% (non condensing)

Environmental (GigaFOILv3 and GigaFOILv3 - PLENUM)

  • Operating Temperature:
       -40C - 70C (-40F - 158F) Continuous
       -40C - 85C (-40F - 185F) ‹72 Hours
  • Humidity: 5% - 90% (non condensing)

Communication and Network Performance
(models as specified)

Auto MDI/MDI-X Configuration

Automatically detects and configures the twisted pair port on the converter to the correct MDI or MDI-X configuration.

Auto Negotiation

Automatically configure 10Mbps or 100Mbps (FOIL 10/100v3)
or 10Mbps, 100Mbps or 1000Mbps (GigaFOILv3, POE, PLENUM and EMP)

Flow Control

Supports 802.3x Flow Control for Full-Duplex mode and Back Pressure for Half-Duplex mode.

Hot Pluggable

Can be plugged in/out without affecting the filter or other links.

Auto Link Restoration

Automatically re-establishes the network link after a link loss.

Communication Standards

  FOIL 10/100v3

  • IEEE802.3 10Base-T (Ethernet)
  • IEEE802.3u 100Base-TX (Fast Ethernet)


  • IEEE802.3 10Base-T (Ethernet)
  • IEEE802.3u 100Base-TX (Fast Ethernet)
  • IEEE802.3ab 1000Base-T/TX (Gigabit Ethernet)

Power Over Ethernet

GigaFOILv3 - POE acts as a Power Sourcing Equipment (PSE) compliant with the IEEE 802.3at-2009 specification and does not require incoming POE.


Filter Housing

  • 20 ga zinc plated cold rolled steel
  • 1" NPS threaded penetration w/brass mounting flange nut and mesh gasket

Power Requirements

  • Input: 100-240VAC; 50/60Hz
  • Output: +5V / 2000 mA maximum
  • DC plug type: center positive


FOIL 10/100v3, GigaFOILv3 and GigaFOILv3 - PLENUM

FOIL Ethernet Filter Drawing

GigaFOILv3 - POE and GigaFOILv3 - EMP

FOIL POE Ethernet Filter Drawing


GigaFOILv3 Brochure