On 2/8/2011 7:30 AM, Brian - N5BCN wrote: > FYI, a follow up to my RFI hunting adventure: > > I ordered a bunch of ferrite cores from Mouser, Part #623-0431176451, at > about $7.00 each. They have a 0.72 inch inner diameter. > > The offending HDMI cables are fairly thick; I could only manage two complete > turns and still be able to snap the core shut. Three turns and I had to > zip-tie the core shut.
That's why I recommend the larger 1-in i.d. clamp-on. They cost more, but you could have solved your problem with one core having more turns. > The cores helped immensely. I achieved the best results with one core with > three turns and a second core added to the cable with two turns, both on the > DVR end of the cable. The RFI has been abated about 95%. > > Question: does the tightest of the coils going through the core have any > affect on the impedance? Not enough to matter. What WOULD help in your application would be to bunch the turns tightly together so that there is more capacitance between turns, which would lower the resonant frequency. The reason that you needed two cores is that the resonant frequency of your chokes is far too high. Study http://audiosystemsgroup.com/RFI-Ham.pdf to understand this. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
