You say new coax, but how about the connectors and adapters? As has been discussed here many times, these tend to be problematic, especially right angle UHF adapters. At high power they may arc, which causes a HIGH SWR problem in the KAT, and a HIGH REFL fault in the KPA500. Also, what kind of antennas? Are they rated for the power you are running?
You didn’t mention the power you are running, but let me emphasize - problems in coax, adapters, connectors, baluns and antennas really come out when high power is in use. Antenna components get stressed from high power and may fail. Pretty much all of us have done this - we build our stations for 100 watts where everything works fine, then after some time add an amplifier which then brings out the problems we didn’t see at 100 watts. The solution is to use the best adapters and connectors you can find (like K9YC, I only use the real, original Amphenol units), and make sure things like baluns and chokes are actually rated for the power you wish to run. Many commercial antennas have “tuning units” that are needed to make the antenna match properly, but are not rated for high power. A great example is the MA5B, which has two different ratings - the main text states 1500 watts, but the fine print states that the matching unit is only rated for a few hundred watts. Of course the matching unit is required for the antenna. These devices contain toroid coils - the toroid itself will heat up when power is applied, and will eventually change its values due to the heat, or crack. When it cools down, it may return to its previous value, only to show the same problem when power is again applied. Of course, if it cracks, it will need to be replaced to work properly. This is also true of the toroid coils in the KAT500, although the KAT has the ability to check for this issue and will throw a fault if the issue is detected. Checking the antenna at low power really is not a good test for high-power problems. Once the power reaches the threshold for the component’s arc or other problem, it will show the issue, but not below. By the way, the relays in the KAT500 are definitely not reed relays, but rather are standard devices that are rated for power. But, like any relays they are not meant to be hot-switched, and will only withstand so many cycles. Having said this, there are very few failures in these relays (they are also used in the KPA500 and many other devices made by quite a few companies). If you wish to replace them, they are available at DigiKey, Mouser and many other vendors. It is the weekend, so you should do some more testing, make sure the antenna components are not problematic (this can be very hard to find), and make sure the antenna system is in proper shape for the power you are running. If you still have a problem after this, call or email Elecraft Tech support on Monday. 73, Jack, W6FB > On Jul 18, 2025, at 11:28 PM, dave ingebright via Elecraft > <[email protected]> wrote: > > I own two Elecraft KAT500 autotuners (main and spare) They are finding > erratic solutions on all three antenna outputs and then fault due to high > SWR. It's driving me crazy due to both exhibit the same problem. One will > find a solution one day, but not the next, or an hour later on the same or a > different band. New coax runs. If I connect the cantenna to the end of the > coax next to the antenna, same condx. Then I go back to it and it's OK. > So today I caught it. Started transmitting, and ATU went to full HIGH SWR and > then into fault mode. Checked the antenna and nothing amiss. I think the > small reed relays that tune the match are arcing or opening up. You guys know > there are some high voltages in these tuners as they tune and operate. How > does Elecraft handle this in their design? > I still think these are the best autotuners on the market, but what the heck. > I have two of these exhibiting the same symptoms. Checked the catalog, $1024 > on sale $25 off. Sheesh > Guess I will call the tech line and see what they say... > //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]
