Hi Coax is interesting stuff. The shielding is only good down to some lower frequency limit. For anything practical that's going to be > 100 KHz.
At the frequencies you *should* use coax at, transformer coupling is the easy way to break the ground loop. In this era of cell phones all over the place, a transformer plus some sort of common mode choke is the standard approach. For things like 1 pps, you should be using some sort of balanced transmission. Twisted pair, or better, shielded twisted pair. You can either run into a balanced receiver IC and dc couple or into a transformer and do something a bit fancier. With the IC you have a maximum voltage offset that can be tolerated. With the transformer you have the cost / delay / possible error in picking up the edges. If your environment is noisy enough, you may have to transport your pps on some sort of carrier. RF and optical both have their fans. None of that is going to be easy. The alternative is to do what you would do in a screen room. Single point ground, everything tied tightly together. Put reasonable filtering on everything in and out. Tie the filters to the common ground point. This also is not easy, but possibly not as hard as redesigning the ins and outs of every box in sight. I have seen this approach used on some *very* large systems. A some what extreme approach (that I have seen used). Forget about all the shielding and stuff. Buy a farm, put up a small metal shack in the middle of a large field. Bring a hand cart with batteries. Run everything on a big copper covered table. Lots of ways to go. Bob -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Attila Kinali Sent: Monday, May 20, 2013 8:08 AM To: time-nuts@febo.com Subject: [time-nuts] Ground loops in measurements? Moin, A couple of weeks ago, there was a short discussion on "bad" connectors and cables and the coupled in noise of those. Summarized it said that measurements in the time-nuts scale are very sensitive to even the lowest noise levels and coupled in signals. But, all the measurements we do are done using some sort of coax which have their shield connected to the case of the devices. As the invovled devices in a measurement are also grounded over their power supply this will lead to ground loops and thus a 50/60Hz noise. Also, because loops are good magnetic antennas, a lot of other noise floating around in the ether is coupled in (eg a nearby radio station). How do you handle this kind of problems? Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown _______________________________________________ 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.