[Elecraft] KX3 - UHF emissions

[Darren Long]

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
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