Vacuum relays can be quite good, as can a proper traditional relay, but all are only as good as the designer's ability to understand ground loops.
All isolation shortfalls come from either the wrong style relay, or a bad layout with ground loops or crosstalk between RF conductors. Many of the problems are because people insist on grounded unused ports, and the ground point has RF currents flowing through a common ground lead with a signal path. Worse yet, what applies to RF isolation generally applies to lightning. Most trouble occurs because people forget the shield carries exactly the same current as the center conductor, and even one inch of path can drop enough voltage to cause a coupling problem. If we look at the highest isolation switches on the market, the RCS-8V and the DXE switches, neither depend on RF shield currents flowing through the circuit boards. Neither use a groundplane transmission line on the boards. Both have connectors on a single flat plate with a design for radically flowing shield currents from the center common point. The sheet metal the connectors mount to is the signal groundplane. Most "trouble" occurs when people try to run RF grounds up through a groundplane on a circuit board or through point to point wiring. This is true in radio, audio lines, and antenna switches. It isn't good for lighting, ground loops, or RFI unless grounds go to a good common wall with very low impedance, solid connections, and well-planned current flow. 73 Tom ______________________________________________________________ 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
