This is where Fred Cady’s book “The Elecraft KPA500 Amplifier and KAT500 Tuner” really helps out. It has an excellent discussion about using the KPA500 with two radios (but not at the same time…). The RF paths need to be switched with a good RF switch, making sure that very little signal from the transmitter gets through to the *other* transceiver’s receiver. Depending on the radios, it is possible for an Elecraft radio to use the PTT line in the AUX I/O connection, and the other radio to use the RCA jack PTT. You have to be very careful with this, however. Modern radios output a 0 - 5 volt signal on their Key output, grounding the output for transmit. This is exactly what the KPA500 is looking for, although the non-transmit level can simply float (all Open-Collector). It is the ground to transmit that is important. Older radios may have a signal that far exceeds these levels, for example the old tube-type radios using grid-block keying may put a large negative voltage on the PTT output. This will not do well in the KPA500 circuitry. In this case the radio should drive a relay that keys the amplifier.
So, yes it is quite possible to have the KPA500 driven from more than one radio through a selector switch. You just have to do it right. A copy of Fred’s book can show you the way. 73! Jack, W6FB And yes, I still really miss Fred... > On Feb 4, 2021, at 3:34 PM, Frank Scolaro <fscol...@mindspring.com> wrote: > > It's a bit pricey, but I use the 1A2R switch from 4O3A: > > https://4o3a.com/1-amp-2-radios-switch > <https://4o3a.com/1-amp-2-radios-switch> > > Works great, switches my KPA between two rigs... > > Frank, W2YK > > On 2/4/2021 1:10 PM, Morgan Bailey wrote: >> I think that here is your answer: >> https://www.dxengineering.com/search/brand/acom/product-line/acom-2s1-automatic-two-transceiver-commutators?autoview=SKU&sortby=Default&sortorder=Ascending >> Granted it is pricey but will probably work for you. >> 73, Morgan NJ8M >> On Thu, Feb 4, 2021 at 10:48 AM Chuck Chandler <chandler...@gmail.com> >> wrote: >>> I've been using the K3S, P3, KPA500 and KAT500 as my main radio. All three >>> antennas are selected by the KAT500. I also have a second radio, an older >>> Yaesu FT-101ZD. This rig can be switched into the lineup in place of the >>> K3S. I sometimes enjoy using the older rig. In this manner the FT101ZD >>> output goes through the KPA, then the KAT. I find the KAT plays well, a >>> little tap of the key will cause it to auto-tune. >>> >>> I'd like to be able to use the KPA500 as an amplifier, but so far it won't >>> key. I've tried the RCA Phono plug into the PA Key jack, but as long as >>> the K3S is connected the KPA won't go into TX without the proper software >>> signal. I did try with the software keyline interrupter a few months ago, >>> but that prevented the K3S from switching the amp unless I also used a >>> Y-connecter and phono cord from the K3S for amp keying. When I did the >>> keying didn't seem as crisp, though. >>> >>> The K-Line is all connected as in the diagram on page 5 of the KAT500 >>> manual. >>> >>> Ideally, I could turn off the K3S, switch the feedline from the K3S to the >>> 101ZD, and have use of both the tuner and amp. Is there an easy way to do >>> this? Perhaps one of those breakout boxes? Any hints appreciated! >>> >>> 73 de Chuck, WS1L >>> >>> chandler...@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 >>> Message delivered to mbaileyc...@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 >> Message delivered to w...@arrl.net <mailto:w...@arrl.net> > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > <http://mailman.qth.net/mailman/listinfo/elecraft> > Help: http://mailman.qth.net/mmfaq.htm <http://mailman.qth.net/mmfaq.htm> > Post: mailto:Elecraft@mailman.qth.net <mailto:Elecraft@mailman.qth.net> > > This list hosted by: http://www.qsl.net <http://www.qsl.net/> > Please help support this email list: http://www.qsl.net/donate.html > <http://www.qsl.net/donate.html> > Message delivered to jackbrin...@me.com <mailto:jackbrin...@me.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 Message delivered to arch...@mail-archive.com
