Ladder-line? THAT is an important piece of information. Open wire line is great. It is very hard to get these days. Almost as great is ladder line. I use a lot of it. It has one pretty big problem - when it gets wet, its impedance characteristics change. When that happens you will need to retune. I say this with a lot of experience. In this case it is not the ATU, but definitely the ladder line.
I will say for the second time, there are NO reed relays in the KAT500 or KPA500. I am very familiar with those relays. They can carry lots of power, but do not take kindly to being hot-switched. My KPA500 code makes sure they are not hot-switched, and I know the code in the KAT500 performs the same way. When we need to break the PTT line to the amplifier, we use a smaller relay that handles the very low current signaling of the PTT line. And yes, we do negate the PTT/Key line if SWR gets out of range. Third, you should be using about 20 watts to tune the KAT500. It performs best at that level. In any case, be sure to read the KAt500 manual - it tells you the correct specs and how you should handle things. Also, while it is a good idea, there is no need to tune the KAT with the KPA500 in STBY. The KAT500 always opens the PTT line when a tune is requested, which directly puts the KPA into low-power mode where it is not amplifying. This assumes, of course, that you are using the proper control cables to connect the transceiver to the KAT500, then to the KPA500. Again, read and follow the manuals. You _could_ have a problem with the KAT500s, but if both behave the same, it is probably not them. As much as we hate going through our antenna systems, that is a must in this case. You really don’t want to send the KATs back to Watsonville only to have them returned with no trouble found along with a repair and shipping bill. Take the time to make sure your antennas really are in good shape. We get lots of reports on this one, and pretty much every time the ham ends up finding something deficient in the antenna system. Just because something works well at 100 watts, does not mean it will at 500. And yes, pretty much everyone who upgrades to an amplifier (including me) found this out the hard way. I learned the lesson and fixed my antennas properly, and still use the very first KPA500 many years after we first powered it up. It is a great amplifier! 73, Jack, W6FB KPA500 firmware developer and engineer of other devices… > On Jul 19, 2025, at 11:35 AM, dave ingebright via Elecraft > <[email protected]> wrote: > > Jim, Thanks for your query. I'm tuning at less than 10W, KPA amp always in > STBY. Sometimes the tuner finds a better match at a little more power (25-75 > Watts); someone else mentioned that, too. > But again, yesterday, it found the solution (Multiband ladder-fed G5RV at > 40') 14Mhz, and everything was fine during the first part of the FT8 QSO, and > then the tuner went to a high SWR fault for no apparent reason. > I reset it, and it was fine for the rest of the operating session. It doesn't > matter what band or what power. Remember, I have two of these doing the same > thing. > I still bet there are a couple of little reed relays with pitted contacts in > the auto tuner. I am sure a lot of us have wondered how they get away with > using those in a ~500W high-voltage environment. I will call the tech line, > but wondered if any of you on this reflector have had this problem > //dave > WB7ELY > ______________________________________________________________ > 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]
