On 5/12/2013 10:37 AM, Jeff Stevens wrote:
Whenever there is AC (or worse yet, square
waves) there is going to be SOME level of RFI, no?
Yes -- but the difference between good design and bad design is HUGE.
The major drivers of this are 1) rise time -- faster rise time = more
RFI 2) minimizing the radiation of RF noise by confining RF current to
transmission lines, and to small loop areas; 3) proper design that
avoids Pin One Problems, including "Pin One-Like Problems" with the
power system green wire; 4) the use of twisted pair for all conductors
carrying those square waves; 5) proper filtering on power wiring.
The question becomes what level is acceptable for a particular installation.
In my case, if it's VLF/ELF noise or HF noise below the noise floor on antennas
some distance away, I don't really care.
Of course. The good news is that the "proper design" above is EASY, and
not expensive, but both the product manufacturer and the installer must
be smart enough to implement it.
Several years ago at an IEEE EMC conference, I heard/saw an EMC engineer
present one of his product designs for an Ethernet router/switch that
was completely unshielded, but yielded excellent results when tested for
emissions.
73, Jim K9YC
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