[SI-LIST] Re: Coaxial Cable crosstalk
- From: C Deibele <deibele@xxxxxxx>
- To: "Daniel, Erik S., Ph.D." <Daniel.Erik@xxxxxxxx>
- Date: Tue, 05 Feb 2002 11:48:04 -0500
"Daniel, Erik S., Ph.D." wrote:
>
> Craig-
>
> I think you're right -- this is a hard problem. In our experience with good
> quality coax cables in the lab, the crosstalk is so low (easily better than
> -100 dB) that I think you'd find it extremely hard to predict -- much easier
> to measure with a good spectral quality signal source and a spectrum
> analyzer with fairly low noise / narrow resolution bandwidth. Because the
> crosstalk between very good cables is so low, you may find that the
> effective crosstalk between signals on the two cables is totally dictated by
> what is happening at the cable ends (e.g., connection to a PCB where the
> signal is not totally enclosed by ground).
>
> If the cables you are interested in are not as high a quality (e.g., thinner
> ground shield with a looser braid, etc.), it may be even easier to measure
> the crosstalk, but it seems it would still be difficult to predict. Can you
> give some more information on the type of cables you are interested in, the
> approximate level of crosstalk you care about, and the frequencies of
> interest? Our limited experience here in the lab was with good quality
> flexible cables with SMA or 3.5mm connectors, looking at frequencies of a
> few hundred MHz to a few GHz, lookinf for crosstalk at the ~-100 dB level.
>
> Some cable manufacturers specify crosstalk per foot or some such thing
> (assuming some cable separation I suppose). I think I've seen this for RG-6
> cable before.
>
Well, I am not interested in any actual cable. I am more interested in
some general theory/theoretical concepts.
We have an application where we have twinax (twinax is like coax, except
it has two conductors surrounded by an outer shield instead of one
conductor surrounded by an outer shield like coax). The frequency is
DC-1MHz or so.
These cables are long....separate sources, and they will all be
collected at a common point where they will share a small space, and
then separate again.
There is some cables with high currents on them...on the order of a few
thousand amps....which may/may not have switching supplies driving them.
So, if I have a small signal cable nearby...how can I reliably predict
what the crosstalk/might be?
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