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
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