Products & Product Reviews

DX Engineering ISO-PLUS Ethernet RF Filters Find Big Fans in the Audiophile Community

History is filled with stories of products that started out as one thing and ended up becoming legends for an unintended purpose. Listerine was first marketed as a floor cleaner before becoming a savior for halitosis sufferers. The Slinky was designed to keep nautical devices stable on rough waters before walking into the hearts of pre-video-game-era children who marveled at its ability to traverse stairwells without the aid of batteries. Before inspiring budding artists, brightly colored Play-Doh was used as a wallpaper cleaner.

The ham radio world is no different. Just as MacGyver could take a paper clip and a roll of twine and turn it into a makeshift zipline, amateur operators have been known to transform an old bedspring and some counterpoise into a functional, if not stellar, antenna.

Which leads us to the DX Engineering ISO-PLUS Ethernet RF Filter

a patent-pending device that hams have been successfully using to suppress common mode radio frequency interference (RFI) and electromagnetic interference (EMI) from well below 1 MHz to 100 MHz and beyond. With no effect on throughput and without change to data signal levels and speed, these filters are easily installed on both ends of Gigabit Ethernet Cat5(e) or Cat6 network cables to filter noise caused by personal computers, printers, multi-port switches, cable modems, routers, radio transceivers, and other devices.

ISO-PLUS filters work in two ways. They can mitigate RFI caused to the Ethernet-connected device, or they can reduce interference to radio receivers and other Ethernet devices that is caused by RFI or EMI generated by an Ethernet-connected device.

Here’s just one of the many ways hams have used the ISO-PLUS in their shacks:

“Five stars: These things work! I was unable to use FT8 on 160 meters at my remote site since internet comes via a Ubiquiti 5 GHz link that kept resetting to factory defaults when I ran more than 400 watts on 160 for more than five seconds. RF was getting rectified and sending reset voltage to the CPU. The ISO-PLUS does not pass POE, but I used a pair of POE injectors to bridge the power through a ferrite loop across the filter. I housed it all in a plastic box and mounted it on the pole below the Ubiquiti unit and it works perfectly! I can run 1,500 watts on FT8 with no problems at all!”

Music to Their Ears

While amateur operators have been realizing the benefits of these handy devices for several years, the audiophile community has more recently embraced the unexpected advantages of adding ISO-PLUS filters for greater enjoyment of streamed music.

From the flood of comments posted on audiophile forums about the ISO-PLUS, it’s clear that music lovers looking for ideal sound quality share the same itch to experiment as do hams. The filter has been the subject of much testing, analysis, discussion, and debate by those more passionate about Brahms than baluns, with a rather vocal contingency of aficionados singing the filter’s praises in terms of performance and cost-effectiveness. For a small investment, the ISO-PLUS has delivered a range of audio enhancements, especially when combined with an EtherREGEN (ER) switch. Here are some of the benefits reported by audiophiles who have installed ISO-PLUS filters:

  • Improvements to soundstage (defined as an imaginary three-dimensional space in a stereo speaker system). Listeners point out the ability to discern the location of instruments and vocals when hearing a piece of music, say, the well-defined sound of an oboe rising above the other instruments in a symphony orchestra. Some describe the ISO-PLUS as adding more “natural depth” to the listening experience.
  • Audio enhancements without degradation of tonality
  • Lowered noise floor, which translates into less masking of finer details
  • Uplift to clarity, transparency, and bass
  • Lack of glare (an unpleasant hard or bright sound resulting from too much low- or mid-treble)
  • Unveiling of nuances in a performance that were not present prior to installation

Audiophiles are experimenting with placement of the ISO-PLUS filters in various locations. Examples include just before the ER, and between wall and Cisco switch, router and Mac Mini dedicated to an HQPlayer, WiFi Extender and Om Deluxe, Network Attached Storage and router, or ER and streamer.

The Verdict?

Should you add the ISO-PLUS to your sound system? We recommend doing your research and heeding the advice of these audiophiles:

  • “They work incredibly well. For little investment just try them out. This is a no-risk story.”
  • “Excellent bang for the buck. If you are running an NAA (Network Audio Adapter) over Ethernet, they are a must-buy.”
  • “World-class tweak. Cost/benefit ratio is incredible IMHO.”

Available in quantities of two or ten, each ISO-PLUS filter comes with a shielded, six-inch double female RJ-45 patch cable. 

To read more about using the ISO-PLUS for improved music listening, do a Google search on DX Engineering ISO-PLUS Music. For many more ham radio-related technical details and reviews, and to place your order, visit

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