On 8/27/2013 1:51 PM, Tom wrote:
The >full shield coax that used a foil were (are) especially prone to ground >loops by not having a good connection at both connectors.
While I agree with your analysis that the problem was a bad shield connection to a crummy cable, there's a bit more to understanding what's going on.
Coax (and other transmission lines) reject noise and crosstalk by providing a low impedance, low reactance path for return current. That is, the current in the center conductor returns in the shield, so the total field outside the coax is zero, and no external field can couple into the transmission line. When that return connection is not there, the current returns by whatever path mother nature finds, a large magnetic field is generated that is proportional to the loop area, and any RF current near that loop is coupled into the circuit.
Yes, one solution is to buy a decent cable. Another is to take a short piece of RG58 (or any coax with a copper braid shield -- the cable is far too short for Zo to matter) and put BNC connectors on each end. If you have a decent crimper for BNCs and some connectors, that's easy. If you don't, it's a bit more work. :)
73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
