On 12/23/2022 1:34 PM, Hare, Ed, W1RFI wrote:
would probably require 30 to 40 dB lower emissions. This would add very
real costs and, with additional shielding needed, add weight to most
electronic devices.
For many (most?) products, shielding is NOT required. FAR more
significant are circuit design issues, like proper termination of cable
shields and the power system "green wire," wave-shaping of power-control
products (SMPS, variable speed motor controllers, etc.), PCB layout and
construction. I strongly suspect that emissions from
Well-laid out multi-layer boards provide significant self-shielding; the
key is that the "ground" layers MUST be continuous. If unbroken, they
form a transmission line with each trace, confining fields to a narrow
region around the trace. If broken, the trace becomes a single
conductor, combining with whatever return circuit is available to act as
an antenna for whatever current it carries.
Shielding between windings CAN be an issue for components like signal
coupling transformers, like those coupling to pairs in Ethernet cables
and other data networks, including DSL. And I strongly suspect that
improper termination of cable shields (the Pin One Problem) is the
primary mechanism for leakage from CATV systems. And poorly terminated
F-connectors have a major cause of leakage since the earliest days of
those systems.
By waveshaping, I'm talking about what Elecraft has done with their
keying envelope to optimize readability while minimizing harmonic content.
None of which changes my assessment of the likelihood of FCC Regs
changing for the better. :)
73, Jim K9YC
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