[RFI] Samsung oven RFI update number II

[Jim Brown]

On 5/22/2020 10:42 AM, Randy Diddel wrote:
> I did look at the board and it is wide open and there is no sign or any shielding

Products shielding is far less important if proper layout and 
construction are employed. If, for example, noisy currents are carried 
on twisted pair, nothing radiates from (or is received by) it because 
return currents and the associated fields are contained within the pair. 
Likewise, when a "ground" layer is employed on circuit boards, return 
current flows on the "ground" layer, forming a transmission line, so the 
field is contained within the small area between the trace and the 
"ground" layer. This falls apart if the "ground" layer is broken under 
the trace.

Short sections of coax or twisted pair are often used inside equipment 
between circuit boards or between sections of a circuit on the same 
board. Well designed equipment can be quite free of RFI issues, even 
when un-shielded, if every path for noisy currents is a transmission 
line. Where this can become impractical is when the current path 
includes some large object like a motor or heating element.

73, Jim K9YC