Something to remember is that your coax switching needs to handle high-power. If it is rated at 500w it will likely fail; go for at least a kilowatt. Manual multi-position switches are common. But using coax relays is an option if you need fast switching for contesting, etc.
Just remember not to switch "hot". That means not when the KPA-500 is transmitting. This will cause arcs, pitting of contacts, possible failure of the output devices in the amp. I recently had an experience running 1250w at 144-MHz where a coax relay overheated and melted the movable contact shorting it out and causing extreme anode and grid current on my 8877. The relay was rated for 1200w at 150-MHz. It was not "hot-switched" as it is controlled by a sequencer. None the less the contact got so hot that is folded 180-degrees back on itself so that it contacted ground in the coaxial cavity of the switch. It is being replaced with a coax switch rated for 3kW. Oh the 8877 is probably OK as it can handle 2500w for short durations. http://www.kl7uw.com/Switch-001_1.jpg So not all manufacturers are equal - check the rating of switches used for QRO. Ratings are all for low SWR and derate when SWR climbs! Also often overlooked is insertion loss in relays (more significant as freq. rises into VHF/UHF). I find the simple open-frame coax bypass switches that are used in most commercial amps are not low loss or flat SWR. My 6m Mirage presents a 1.4 SWR to the K3 when its in bypass and I have a 50-ohm termination on the amp. Power loss is about 1w (of the 8w output of the K3/10). That is about 0.6 dB. Typical loss of VHF coax relays is 0.05 dB No one would confuse a Mirage with "quality", of course. The simple fool-proof switch is to connect cables manually. -------------------------------------- Message: 41 Date: Sun, 10 Jul 2011 07:58:47 -0700 From: "Dick Dievendorff" <die...@comcast.net> Subject: Re: [Elecraft] KPA-500 Question To: "'Fred Maas'" <just.one.h...@gmail.com> Cc: Elecraft@mailman.qth.net ===snipped==== The Antenna1 output of the K3 goes to the KPA500 transceiver in. The KPA500 output goes to the antenna switch common. The antennas connect to the antenna switch. ============= Some amplifiers have a couple of antenna outputs. Ours doesn't. Whatever number of antenna connectors we chose, other than one, would be too few for some and too many for many. 73 de Dick, K6KR 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com EME: 50-1.1kw?, 144-1.4kw, 432-100w, 1296-60w, 3400-? DUBUS Magazine USA Rep dubus...@gmail.com ====================================== ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
