Anyone who has looked inside a good coaxial relay or switch knows that for that level of isolation the mechanical construction one needs to provide a more or less complete shield around the chosen signal path, that re-forms around the new path when the swich is operated. This is complicated and expensive. I would not expect to find it in a normal HF amateur transceiver, tuner, or amplifier. Maybe in some specialized equipment for multiradio operation, SO2R or otherwise. It is certainly something to be hoped for in future equipment. However, one should not be very confident that a switch with high isolation numbers would always prevent the sort of signal leakage mentioned in this thread. "Transmitting on a dummy load" is a common expression, but I guiess it is seldom representationve of what is actually going on. More likely, some signal is flowing as on the outside of shields, and needs common mode chokes for suppression.
This point is well known to high-end competition stations that depend on separate receive antennas for the low bands. The job of such a receive antenna is generally not to pick up as strong as possible version of the wanted signal, but to pick up an adequate sampling of that signal along with less noise covering up that wanted signal. This involves avoiding noise pickup where the feedline runs through a high-noise environment (read: the shack building), as well as long distance signals coming in from the back of the receive antenna. (A conventional "front-to-back" number is not much help, one must rather use a complicated measure of back side rejection over all applicable "back" direction angles.) Noise pickup on the outside of coax will generally nullify the performance of a well-designed receive antenna that looks good on paper, unless the installation includes liberal common-mode choking and grounding of coax shields. I seem to remember one report that said the grounding was so critical that a ground connectied only to one side of the coax was markedly infererior to one that completely encircled the coax. Installations normally include running the coax through metal conduits, not just for mechanical protection, but for blocking noise pickup. If it is not already obvious to the reader, I am referencing noise pickup on receive antenna feedlines as something that corresponds to transmit capability as well, allowing transmission "on a dummy load" even if the dummy load is perfectly shielded. Bottom line: Leakage and crosstalk is a system characteristic that results from more than the performance of a given component such as a switch. 73, Erik K7TV -----Original Message----- From: [email protected] <[email protected]> On Behalf Of ANDY DURBIN Sent: Saturday, July 07, 2018 3:54 PM To: [email protected] Subject: Re: [Elecraft] KAT500 antenna port isolation "I suppose the only way to get good isolation data will be to do a sweep of the KPA500 and Alpha Delta switch" Sorry - that should have read "I suppose the only way to get good isolation data will be to do a sweep of the KAT500 and Alpha Delta switch". TMGS? 73, Andy k3wuc ______________________________________________________________ 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 Message delivered to [email protected] ______________________________________________________________ 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 Message delivered to [email protected]
