I have an odd issue - SWR swings wildly, like a loose connection (there are no loose connections), on 17 and 15 M, only mid-afternoon local. I have made contacts as far as Japan (from central NC) at other times of the day. Also, the SWR issue is intermittent; many days I can work 17 and 15 mid-afternoon with no issues.
It happens more often on hot days - maybe related? But, shack temperature doesn't fluctuate. I have tried turning off AC, in case that was interfering.
The radio shuts down transmit when this happens.
Radio: Icom IC_718
Antenna: dipole trimmed to 80 meter band
Feedline: 400 ohm window line
EDIT: Additional info - The problem goes away if I bypass the tuner, but, if I use the dummy load in the tuner, I still have the erratic SWR.