[Elecraft] RFI

[Jim Brown]

On Tue, 10 Nov 2009 10:29:39 -0400, robby robertson wrote:

>I thought my microKEYER was guilty of RFI but it turned out that the audio
>patch cables for line in and line out had a less than 10% shield. I
>temporarily solved the problem with ferrite but a more permenant solution
>will be RG-58au.

Your assessment of the problem is wrong. The problem is NOT shielding of the 
cable, it is either a pin 1 problem in the equipment one end or the other of 
that cable or RESISTANCE in the cable shield. There are two possible fixes 
for a pin 1 problem, one of which you found. The other fix is to rewire the 
defective equipment to eliminate the pin 1 problem.

Both pin 1 problems and shield resistance couple shield CURRENT into 
equipment. A ferrite reduces RF shield current. If it's resistance, RG58 
with a robust copper braid shield will help because it has less resistance, 
not because it's better shielded. If it's a pin 1 problem, it won't help. 

Another point. That cable is acting as a receive antenna. Changing the 
length (or orientation) of ANY antenna can change its behavior. 

For a tutorial on all of this see 

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

73,

Jim Brown K9YC