Definition and Determination of Coupling Length in Multiconductor Shielded Cables

Hi, I am responsible for trying a new test for transfer impedance of a multiconductor shielded cable but I am not familiar with some of the terminology. What is the coupling lenght of a sample of cable wire and how is it deteremined?

Hi Emmanuel,

Cable wires and coupling length, can you expound more of this case? It seems you are into a transmission lines topic related to electromagnetics. Images if you do have, so that some experts here can also help. Thanks

Best,
Neil

Thanks Neil,
This is not a transmission cable but rather a datacom cable that happens to be shielded. It is a multiconductor cable. However when testing for transfer impedance, the coupling length is required (Triaxial Chamber method ). I understand that coupling has to do with the transfer of energy between two adjacent wave paths but am not so sure what "coupling length" refers to. This is in the arena of electromagnetism.

Yes, it is in electromagnetism in which this coupling length depends on the given parameters in order to have it. Multiconductor cables are in different forms/setup including materials that may effect the coupling.

Try to check this resource link -> "Coupling Length('')":http://przyrbwn.icm.edu.pl/APP/PDF/116/a116z462.pdf

Thus, cables related to electromagnetism is quite tough because it is not limited to measurements alone but also the materials that needs to be considered. EMC experts can facilitate or further discuss this issue.

Hope it helps.

Best,
Neil

Firstly, all cables are transmission lines.
You are presumable testing to a standard that exists, IEC, or whatever, the standards normally define the terminology and test parameters, if they don't, that is a bad oversight on the part of the standards authority.
I assume that the test setup for measuring transfer impedance includes some form of cylindrical conductor through which the cable being tested is threaded, and that it probably has a defined length for the test, which may be the coupling length.
As I said, standards normally carefully layout the test parameters, so the information should be there,
cheers,
Richard

Hi again,
have a look at the file enclosed, it has some info that may be of use Note, as I said before, all cables behave like transmission lines, so although this paper discusses HV power lines, it makes no difference as far as the electromagnetics is concerned, all that changes is the characteristic impedance. I believe that in talking about a 1m test length, that this is the coupling length. This is not my area of expertise, if necessary, talk to people that do standards testing, they should be able to clarify what it is you want to know,
cheers,
Richard

Hi Richard,

Thanks for the file. On further inspection, the network analyzer gives a description of what the coupling length is in regards to the sample under test. It turns out the coupling length is the same as the sample length under stress. So yes the coupling length is 1m and when we got close to the desired results when we went with that.