Several weeks ago, in the ARRL RTTY Roundup, I noticed a weird effect when sending in rapid succession: over several seconds, the SWR at my radio ramped up to ~3:1, consequently my transceiver folded back its output power. After maybe 20-30 seconds of rest, everything resumed to normal again.

On first hunch, this looks much like a thermal issue, something is heating up and cools off to revert to normal. On to debugging my antenna system. A quick test with a dummy load hooked directly to the transceiver showed no problem with either PA nor power supply.

Rain, work (and skiing, I admit) kept me from looking closer at the outside antenna components; besides, with lighter load cycles e.g. in CW, no repro. But this weekend, there was yet another RTTY contest, CQ WPX RTTY.

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