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Impedance control on LISN power output
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jmw:
A 50u/50 ohm DC LISN should look like this:


It's supposed to present a 50 ohm || 50 uH impedance looking in from the output, i.e. Z_in should be a flat 50 ohm above 160 kHz. How is this meaningful in practice when the LISN is connected to the DUT with straight wire that adds series inductance? The examples of LISN either have banana-style terminals (DC) or mains plugs (AC) so no impedance control. Similarly, the connection from the bulkhead power ports to the LISN board doesn't appear to be impedance controlled either.
bjbb:
CISPR16-1-2 is the basic guidance for ISNs. Note the frequency curves for max and min Z; that is the characteristics of your particular ISN is dependent on the data generated by your calibration contractor or however you get your calibration plots.

Some generic EMC standards have both normative and 'suggested' ISN connections; and some do not. In any case, I have not seen 'banana' connectors for the AWM output on anything made in last 10 or 15 years.

Power wiring out of the ISN and into the UUT, at frequencies intended for conducted emissions measurements of appliances, should be representative of the intended end-use.

Typically, mains impedance of the in-line components are much higher than that added by conductors for appliances and IT equipment. Power into the ISN is generally assumed to be per a narrow range of Z.
jmw:
I found this article (https://incompliancemag.com/article/topology-and-characterization-of-a-dc-line-impedance-stabilization-network/) with pictures and it looks like they measured the output port impedance by running coax from a VNA up to a custom-job adapter that is as small as possible. For a banana plug style output, a similar construction could be an off-the-shelf BNC-to-banana adapter. I'll also read about what the standards say about suggested connections..
T3sl4co1l:
The LISN-to-EUT wires need to be 50 ohms (or 100 ohms differential, in the mains case), yes.

Alternately, everything after the LISN is considered EUT.  It is a good idea to provide a standard cable length with the product (and recommend the same in the manual), and test with that.

Tim
coppercone2:
and a better idea to make sure it works with whatever plugs into it because you know that will happen

if we lived in a perfect 50uH electrical world. A sweepable ISN inductance would be interesting

perhaps since the coils are usually split into segments, relays could be added to short out segments to change it?
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