[Elecraft] KAP1500 High SWR wen unkeying with FT8

[Ac9c]

I had that thought as well. I was also wondering if the cause was unkeying the amp while the IC7300 was still transmitting. To test that I’m going to manually key the amp and then start & stop FT8 transmissions while the amp is keyed. I also have a wide and receiver and directional coupler that I may be able to capture the TX spectrum from the radio at the instant the FT8 transmission ends…

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On Thursday, June 11, 2026, 11:35 AM, Andy Durbin via Elecraft <elecraft at mailman.qth.net> wrote:

I had a problem with high SWR when unkeying a TS-590S used with KAT500 and KPA500.  It was a challenging investigation.

I found that, due to the failure of an electrolytic capacitor,  my TS-590 was emitting a short burst of RF on a completely spurious frequency when it was unkeyed.  The failed capacitor changed the rise time of a TX/RX switching signal and resulted in an unintended oscillatory loop.

The spurious frequency was way off the frequency to which my antenna was tuned so I received a high SWR indication.

I'd suggest you use appropriate tools to examine the frequency of the amplifier RF drive signal for the TX/RX transition.

73,
Andy, k3wyc



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