On 12/6/19 9:10 AM, Dana Whitlow wrote:
Even without any funny business with boost converters (or whatever). those
copper wires
make a nice antenna for coupling noise from both ends (PC and USB
accessory) into
the environment inside the chamber. Unless, of course, the cable is
well-shielded, which
you did not mention.
I suppose it's too late to ask, but did you perhance try adding some
clamp-on ferrite chokes
to the cable?
We had a similar problem doing some testing on hardware in a EMI/EMC
chamber where we wanted to measure fields well below the MIL-STD-461
RE102 limits at HF frequencies.
Get some 31 mix toroids in the 2.4" diameter, and you can get a lot of
turns of the cable through it and the hole is big enough to clear most
connectors. There are also clamp-on forms. 31 mix has a nice wide
range, although I don't know if it goes down to 100kHz.. there might be
a better mix.
You definitely don't want the usual VHF suppression mixes like 43 or 61.
But maybe mix 78, which is optimized for <2MHz
In this kind of application you want to look at mu'' (the lossy part of
permeability) as well as mu' (the non lossy part)
Or, as you plan to do, run stuff off batteries.
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