Re: KAT500/KPA500 - Sanity Check Please

Posted by Dick Dievendorff-4 on Jan 26, 2019; 6:25pm
URL: http://elecraft.85.s1.nabble.com/KAT500-KPA500-Sanity-Check-Please-tp7648517p7648536.html

Andy:

If the RF power is high enough, and the bypass SWR is high enough, the ATU will fault and interrupt the amp key line. I’m away from the code right now, but we named this fault something like “power too high for bypass SWR”.

This is distinct from another SWR-related fault when the matched SWR, as seen by the amp, exceeds a threshold. This is the “amp key interrupt threshold”, and you can set that.  Some users want this out of the way, they trust the amp to protect itself, so they set this to 99:1. I think it defaults to 3:1.

There are two SWR-related faults, both interrupt the amp key line.  One is based on SWR as seen by the amp.  The other is the SWR of the antenna, measured with the ATU bypassed, the bypass SWR, with RF power too high.

If the SWR seen by the amp is low enough, the amp doesn’t care what the bypass SWR is, as the amp doesn't see that SWR.

ATU components have voltage and current ratings that might be exceeded if higher power is permitted with a difficult load. This is why 10:1 bypass SWR can’t be allowed at 1000 watts, even if the SWR seen by the amp is 1.000 to 1.

It is inconvenient (sometimes impossible) and too slow to measure bypass SWR every time a tuning solution is recalled.  So this bypass SWR is measured during a full search tune and is retained in the stored ATU setting.

I’m on vacation and we are about to head out, so I’ll need to let this go for a while.

73 de Dick, K6KR

> On Jan 26, 2019, at 11:36, Andy Durbin <[hidden email]> wrote:
>
> "The ATU does interrupt the amp key line when the bypass SWR is too high AND there is enough forward power to endanger ATU components. It’s a fault."
>
>
> Dick,
>
> I'd like to understand that a bit better.  Are you saying that, with a tuning solution that gives 1.6:1, and with that tuning solution being active, that the bypass SWR is being used in the logic that controls the interrupt line?
>
> I would not have expected the bypass SWR to be used in this condition. With the tuner in-line isn't  the instantaneous SWR and reflected power what controls the interrupt?
>
> In other words - isn't the bypass SWR only a factor if/when the tuner is bypassed?
>
> Thanks and 73,
> Andy, k3wyc
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