[Elecraft] PX3 noise generated on KX3-2M

[Jim Brown]

On Tue,2/23/2016 10:26 AM, David Anderson wrote:
> I wrote about my experience and how better grounding of the DC socket of the PX3 to the chassis reduced the radiated noise.

David,

Thanks for posting this. I've been bugging Wayne about these issues for 
more than ten years, and he still hasn't gotten the message. This is a 
great example of ignoring what EMC guru Henry Ott calls "the hidden 
schematic lurking behind the ground symbol," and which is a primary 
cause of EMC failures (RFI, hum, buzz). In the pro audio world, we call 
it "the Pin One Problem," whereby cable shields fail to contact the 
shielding enclosure at the point of entry, but instead go to the circuit 
board, finally reaching the chassis via a path established by the whim 
of the PC board layout artist.

One VERY important correction to your post.  This connection is NOT a 
"ground" or "earth," it is a BOND between the cable shield and the 
shielding enclosure. Or in the case of the power connector, between DC- 
and the shielding enclosure. The significance of this is that without 
that bond, RF can be coupled to that cable and radiated by simple 
antenna action. In addition, RF can be coupled from one cable shield to 
another, and from there to an input circuit.

A connection to actual EARTH is NOT part of a solution to these 
problems, proper bonding IS critical to the solution. Neil Muncy, 
ex-W3WJE (SK) put this quite poetically in the tutorial workshops he did 
for audio professionals. Neil said, "Buy a six pack of your favorite 
beer, grab a chair and a set of good binoculars, and sit at the end of 
the runway of O'Hare (substitute your local airport) and CALL ME COLLECT 
when you see an aircraft take off trailing a ground wire."

73, Jim K9YC