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RF-Protection filter for DSL-Modems


This LP-filter protects DSL-modems from RF-Interference caused by RF from your transmitter. Specially when transmitting on 160m and 80m it’s very common that the RF cause interference or even make the DSL-modem to reset.

The attenuation is >40dB on 160m and >60dB on 80m. 

You just connected it between the DSL-splitter and the modem. Move the RJ12 connector from the modem to the filter “Line” jack and connect the short cable with RJ12 connectors (included) between the “Modem” jack and the modem.

Be aware of that the filter can cause a degradation on the DSL-download speed if you have a DSL connection with 10 Mbit/s or higher. But you do not use the high speed anyway for the remote control so the possibility to work on 80 and 160 is well worth the eventual loss of download speed.

Drawing. Installation/cables


 image Background: 

This is not a new invention the design is based on a schematic which has been available on Internet for some years. I had problems running even 50w on a  80m dipole quite near the phone line. The ADSL modem restarted as soon as I transmitted. I assumed the problem was more of common mode type and I tried with ferrit rings etc. without much result. Later I heard other who have get rid of the problem with this DSL-filter so I decide to try. After building and installing this filter I could run 1kW without any problem. I was so impressed over the function so I decide to make the filter available to our customers via the webshop immediately. But at that time I didn’t find a cheap and “ready to use” housing so I put the project on hold. By a coincidence I run over this box and it was the solution to make the filter reproducable to a resonable cost.


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