Wednesday, November 9, 2011

Toroid choke for VDSL modem

I noticed that my transmissions on 3740 kHz were often accompanied by a loss of sync on the VDSL modem that provides U-verse service to my home. This is not surprising, given the frequency spectrum used by VDSL and the proximity of my dipole antenna to the aerial service drop that brings phone service and U-verse to my home. I obtained a large diameter ferrite toroid -- FT-240-J from Amidon and installed it on the DSL line cord at the modem. The 'J' material is designed to provide excellent attenuation in the 0.5 to 20 MHz range. Below is a photo showing the installation.


This toroid is large enough to thread multiple turns of the DSL line cord with the RJ-11 plug attached. Since the toroid resolved my interference issue, I could install a smaller toroid with the RJ-11plug temporarily removed, and save the large toroid for future troubleshooting or other problem resolution.

Update 6/20/17: This toroid should be effective on higher frequencies also, up to the 20 MHz top of range quoted by Amidon. At my past QTH I needed this toroid for 75 m only. 40 m and 20 m were not affected. At my present QTH the VDSL modem was replaced due to a lightning surge, and the new modem was not susceptible to interference.