[sdiy] Poor man's EMC testing?

[Barry Klein]

Am I wrong or am I sensing a bit of email hostility in this topic?
I don't really understand it, and maybe fingers are pointing at what I
suggested and I just don't get it..

My suggestions were pointed at someone with the inability to borrow/use a
spectrum analyzer or perhaps not knowing that one can be had for under a
grand.

While my management hum hawwed about getting our group a spectrum analyzer
I got the sniffer probe set and preamp and used it with my LeCroy.  True, my
LeCroy was probably a 30 grand scope in its day, but now is likely an under
1 grand scope.  It worked fine for finding fundamental freq. issues - those
under the 330Mhz that someone mentioned.  Knock down the fundamental the
harmonics usually follow.  Thing is if you have never done this sort of work
you are on your own doing DIY experiments, reading a ton about it on the
net, and just continually trying things to reduce the emissions.  Components
used, layout, pc grounding, enclosure grounding, bypassing, clock series and
termination resistors... all comes into play.  EMI tape helps but
management usually hates it.

Now if you don't have a scope even capable of the FFT mode and you still
want to do something... but not pay someone, and not buy a spectrum analyzer
but maybe find critical areas try making a sniffer probe off what you'll
find on a google search and build a preamp like I did using a mini-circuits
amplifier, feed it in to your scope and just probe around looking for signal
sources.  Some will make sense and others may surprise you.  Try fixes
mentioned above and maybe you'll have less test time at the "real" lab.


Barry