There is another big consideration in modern ATUs which use toroid cores for the inductors. The cores will heat up during transmission, especially for bad mismatches. Remember, the ATU still has to deal with the high reflected power as it provides a good match for the radio. If the heating reaches a critical level, the toroid will break, and the ATU will no longer be able to do its job. ATUs are thus rated for the amount of reflected power (thus SWR) they can handle with some margin for failure. An ATU like the KAT will handle higher mismatches at low power, but when you start trying to push lots of power through it, the heating margins drop, meaning that you should really watch the match when trying to run a kilowatt through an ATU in order to avoid damaging it. At 50 watts the KAT should handle a pretty bad mismatch, while at 500 a lower maximum mismatch should be observed.
Also note that at higher power the connectors, adapters and coax cable will also see lots of heating with big mismatches. These can fail also; in fact we see that a lot. That’s why you see lots of admonitions to only use high quality connectors and adapters. Right angle adapters are especially bad as the conductor tends to migrate and short out at high power. Be sure that you use coax that is rated for the power levels as well. 73, Jack, W6FB > On Jul 11, 2021, at 3:51 PM, Alan Bloom <n...@sonic.net> wrote: > > I can't speak directly about Elecraft tuners, but I did design an antenna > tuner when I was at Drake many years ago. > > We specified the Drake MN-2700 at 5:1 SWR. I made sure it would match that > SWR at all phase angles on all specified bands. > > Typically the low-impedance end tends to be the hardest to match, at least on > the low bands. So 50/5 = 10 ohms resistive is harder to match than 50*5 = > 250 ohms resistive even though the SWR is 5:1 in both cases. That's because > the low impedances need larger tuning capacitors. The Drake tuner would > typically match well above 5:1 into a high impedance but only barely meet > spec into a low impedance. I suspect the Elecraft tuners are similar. > > Alan N1AL > > > On 7/11/2021 12:58 PM, Al Lorona wrote: >> This question is about how manufacturers spec the matching range of their >> antenna tuners. >> >> If an antenna system presents an impedance of 5 + j0 ohms to the antenna >> tuner, that's an SWR = 10 to 1. >> >> But, an antenna impedance of 50 - j143 ohms is also SWR = 10. So is 110 - >> j200 ohms. >> >> When a manufacturer like Elecraft says, "Our antenna tuner can match a 10:1 >> mismatch," does that mean the tuner can match the first case above, the >> second case, the third case, or all three? >> >> I guess what I'm asking is, are all of the impedances above equally >> difficult for the same tuner to match? Or is one 'harder' than the others? >> It would depend on the values of the L and C in the tuner, wouldn't it? >> Which implies that certain 10:1 mismatches are not tunable? >> >> Thanks, >> >> Al W6LX/4 >> >> ______________________________________________________________ >> 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 a...@elecraft.com <mailto:a...@elecraft.com> >> > > ______________________________________________________________ > 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
