[Elecraft] K3 CAT noise

[Jim Brown]

On Fri, 22 Aug 2008 09:20:21 -0700 (PDT), Paul Fletcher wrote:

>I had similar problems and traced this to the shielding of the cable. I
>found that the shield needed to be connected to the shell of the d-type
>connector at both ends of the cable (soldered directly to the shell) to get
>rid of the interference.

Not surprising. The ONLY good connection for a cable shield is the shielding 
enclosure of the devices being connected. Without that connection there is no 
shielding. A connection of the cable shield to wirng inside the box often 
excites what is commonly known as "the pin 1 problem," which is a form of 
common impedance coupling. In the case of the noise SOURCE, noise is coupled 
onto the cable shield and radiated by the cable shield. In the case of a 
VICTIM, the noise is received on the cable shield and coupled into the victim 
equipment. 

Another point. If the noise is being leaked from the differential signal on 
that CAT wiring, it can be DRASTICALLY reduced by using good twisted pair 
cable (for example, CAT5/6/7). 

The Pin 1 problem is discussed in detail in 

http://audiosystemsgroup.com/RFI-Ham.pdf 

73,

Jim Brown K9YC