http://hfdesign.otg/tt120199.htm says they are used to prevent "unwanted emissions."
My understanding is that a wire (e.g. Ethernet, USB cable, etc.) connected to a device that works at high frequencies (e.g. 2 GHz computer) can act as a transmitting antenna. So in a desperate attempt to get FCC approval for their failing device a manufacturer may add ferrite cores to keep high frequencies from getting out. The fast/cheap way to do this is to put the ferrite core on the wire itself. If the cable is shielded it may not matter which end gets the ferrite core as the radiation problem is with what is attached to it (e.g. a keyboard). >I see those ferrite cores on lots of cables. I have several analog video >cables (HD-15 connectors) with them. Since there is a connector on each >end of the cable but the core is only on one end, it's not clear the >purpose. There doesn't seem to be any instruction as to which end of the >cable goes where (computer/monitor). I've always guessed that they were >spike protection rather than interference protection -- high voltage that >manages to get on the data lines starting, e.g., from the cable / >telephone line Internet connection. Is there any credible "official" >statement as to their purpose? ************************************************************************* ** List info, subscription management, list rules, archives, privacy ** ** policy, calmness, a member map, and more at http://www.cguys.org/ ** *************************************************************************
