[Elecraft] Question about antenna matching

[Bob McGraw]

Do note that the "Typical Matching Range and Power Limits" as stated on 
page 2 of the KAT500 manual.   Pay particular attention to the power 
handling and SWR range between 1.8 - 2.0 MHz.   The SWR limits are to 
5:1 Low impedance,  and 10:1 High impedance.

In the 3 - 30 MHz range the power can be 1000 max but with only a 3:1 
SWR or better.

Also note the Duty Cycle statement regarding power rating being ICAS, 
thus being equal time on and off with a 5 min. limit max at full power.

If you aren't sure, then err on the conservative side so one won't let 
the smoke out of the box.

73

Bob, K4TAX


Message: 2
Date: Sun, 11 Jul 2021 16:17:43 -0500
From: Jack Brindle<jackbrindle at me.com>
To: Elecraft Reflector<elecraft at mailman.qth.net>
Subject: Re: [Elecraft] Question about antenna matching
Message-ID:<7CC60665-E824-4132-BC62-014D695D7C79 at me.com>
Content-Type: text/plain;	charset=utf-8

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 7/12/2021 10:24 AM, elecraft-request at mailman.qth.net wrote:
> Message: 2
> Date: Sun, 11 Jul 2021 16:17:43 -0500
> From: Jack Brindle<jackbrindle at me.com>
> To: Elecraft Reflector<elecraft at mailman.qth.net>
> Subject: Re: [Elecraft] Question about antenna matching
> Message-ID:<7CC60665-E824-4132-BC62-014D695D7C79 at me.com>
> Content-Type: text/plain;	charset=utf-8
>
> 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