Blue Mountains Amateur Radio Club

Ferrite is your friend, and more often than not, the simplest solution to RFI problems.

We all know how frustrating it can be, when you want to operate on HF, and you're voice comes through the speakers on the stereo, or in extreme cases, the mouse on your computer ceases to function. (RF entry into any of the USB leads, even at relatively low levels, will cause the USB controller in the motherboard to lock up, requiring a hard reset.)

I recently had issues with RF entering the audio leads to my PC (I was using PSK31) It was causing the sound card to glitch, and even stop functioning altogether at times. (Mainly on the lower HF bands)

By simply looping the audio leads through a suitably sized ferrite toroid, I was able to cure the problem - cheaply and effectively. (See the included picture)

This remedy will also work nicely on phone lines, speaker leads and RCA line level leads to HiFi systems and AV equipment. In some cases, RFI can be caused by entry through the mains, in which case, looping the power cord to the affected device through a large enough ferrite former, will suppress the RFI. (Mains related RFI is not as common, as most compliant equipment sold in our fine country contains common mode RF suppression on the mains input already.)

As a rule of thumb, around 5 - 10 turns through a toroid will provide adequate suppression in all but the most extreme cases. If the suppression is not sufficient, just add more turns, or even more toroids. The toroid should be located as close to the affected appliance(s) as possible.

73 from James, VK2TIM