Hi Jim, Thanks for the informative response. I dug up a fairly hefty blue torroid that a colleague gave me some time ago when I was lamenting about a different RFI problem and managed to get about 8 turns on it. That has made quite an improvement, 2 or 3 s-points at least. I also discovered that if I grasp the left side end-plate handle (I have SideKX end-plates fitted now, but the problem predates their installation) the spurii drops down to a mere S1. I'm not sure what this means yet, though.
I'll investigate the ferrite appraoch further. Cheers, Darren On 24/06/14 22:14, Jim Brown wrote: > On 6/24/2014 12:00 PM, Darren Long wrote: >> I already have a ferrite on the I/Q cable, but that doesn't help. > > The root cause of what you are experiencing is a "Pin One Problem" at those > connectors. They SHOULD be screwed down to the shielding enclosure, but they > are > not. That's the definition of a Pin One Problem, and it provides a path in and > out of equipment for RFI, hum, and buzz. And I've been banging on Wayne for > nearly ten years about it. > >> Is there anything I might try to mitigate this? > > Ferrite cores can help, but all ferrite cores are not created equal. Most > widely used ferrites used for suppression, like Fair-Rite #31 and #43, peak > around 150 MHz, and are losing their effectiveness at 300 MHz. We can move the > resonance down by winding turns, but we can't move it up. For that we need a > different ferrite material. > > For low UHF, Fair-Rite mix #61 is probably the best bet. Given the strength of > these spurs, you will likely need several on each cable. A single turn > through a > typical #61 core resonates around 600 MHz. Two turns would move the resonance > down a bit, to perhaps 400 MHz, and would double the choking impedance. Buy > the > longest cores you can find. See the Fair-Rite catalog, which is online. > 0461164281 is 0.25-in id., and should hold at least two turns if the cable is > fairly small. > > And don't overlook the obvious -- can you move the scanner antenna farther > away > from you shack? > > 73, Jim 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 > Message delivered to darren.l...@mac.com ______________________________________________________________ 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 Message delivered to arch...@mail-archive.com
