[Elecraft] K3 high SWR at end of transmission

[Michael Carter]

Hi Tom,

This has been an interesting thread to read even though I don't use external software that issues the SW; command. The person who posted a link to a YouTube video of the KX3 doing similar anomalous reporting of SWR indicated that this issue appears to be a longstanding one.

The K3 (and presumably KX3, maybe other Elecraft radios) polls the FWD and REFL arms of the SWR bridge on a schedule I've not tried to monitor.  If the rig receives an SW; command, presumably it reports the last polled value stored in a register somewhere.  A high reported SWR at the end of any transmission, no matter how brief, could result from the FWD value having dropped to zero (or close to it) because the transmission has ceased, but the REFL value was not updated from its last polled value when it should be zero (or whatever value corresponded to the SWR during the bulk of the transmission).  If, as one commentator on the YouTube video page suggested, the time delay between the storing of the FWD value and the REFL value is great enough, then a falsely high SWR could be reported out in response to the SW; command.  The K3 internal polling of the SWR bridge arms may cease when PTT or VOX  is no longer asserted, so it is not reporting the fictitious SWR seen in response to the SW; command.

I don't believe you have a hardware fault of any kind - this is an artifact of the K3 firmware and possibly a time delay between polling the two arms of the SWR bridge.

73,
Mike, K8CN