[Elecraft] KX3 - UHF emissions

[Jim Brown]

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