In article . com,
wrote:

Telamon wrote:

A small loop like the one you built is a classic H field sniffer I have
used to look for RFI problems in switching power supplies. You could
also build a short E field sniffer antenna by extending the center
conductor of the coax a few inches (about 3 inches would be good). Use
shrink sleeve over a heavy gauge wire would make a good E probe.

--
Telamon
Ventura, California

A friend sent me a link to a very interesting pdf,
www.conformity.com/0211field.pdf .
The part about using the tracking signal generator and a directional
coupler to find unexpected resonances was very useful.

I never did that. I did use the tracking generator and spectrum analyzer
to sweep the EMI filter sections that were a part of the supply to see
how well they worked attenuating EMI. I made improvements in the filters
based on that information.

That PDF is a very good primer on EMI / RFI problems and at the time I
was doing that work I had to figure out the strategies outlined in that
document myself with the exception of using using the probes /
directional coupler as a type of grid dip meter. This would be an
excellent proactive technique that I could have used when I was doing
that kind of work years ago.

What he recommends for a sniffer loop an inch in diameter in figure 2 is
over kill in my opinion but would be very well worth the effort if you
were to make a loop larger than a few inches in diameter for hunting a
more distant source than poking around the insides of a box of
electronics. I don't think a BALUN would make much of a difference in
what a 1 inch diameter loop with a split shield would pick up inside a
box.

You can tell that this document was written years ago because it states
Scott Roleson works for HP, which is now Agilent.

Very interesting pdf document, thanks for pointing it out.

--
Telamon
Ventura, California