Hi If you have an electrostatic field to worry about, a simple shield does a fine job. If it’s a magnetic field - maybe not so much. A propagating electromagnetic field is going to be a bit tough to stop.
Again it comes back to Bert’s question - what is the objective? Bob On Jul 21, 2014, at 12:24 AM, Chuck Harris <cfhar...@erols.com> wrote: > Hi Bob, > > I agree, but most of the time, you can use good design > practices to keep the currents flowing through the outside > of the shield to a minimum... avoiding ground loops, stuff > like that. > > Simple coax is used for shielding very high gain circuits > from 60Hz noise all the time in PA systems. > > -Chuck Harris > > Bob Camp wrote: >> Hi >> >> Yup >> >> It is impractical to make coax that has a shield thickness of 1/3”. Even if >> you >> do, it’s not going to be very flexible. For a real world system that needs >> good >> isolation, coax is not the way to go below 100 KHz. There are a few other >> issues >> that come up, but skin depth is a big part of the problem. >> >> Another part of the equation is (as Bert points out in another thread) “how >> good >> do you need?”. Skin depth simply the point that you have knocked out 2/3 of >> the >> current. That probably isn’t what you are after when you ask for “good >> isolation”. >> The “inside” of the coax should be below 170 dbm/ Hz to be “quiet” when >> terminated. If you have -70 dbm / Hz noise signals running around here and >> there, >> you need quite a bit of isolation. You might have a spur spec rather than a >> noise >> floor spec to meet and that would give you different numbers to go after. >> In most >> cases you will need multiple skin depths (like 10 or more) to get the job >> done in >> a noisy environment. >> >> Bob > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
