FT840 with g5rv at 40'
I've had several occasions when a seemingly strong signal couldn't be tuned so I could understand it. sound was like I was off freq. but tuning above and below to loss of signal didn't clear it up. Receiver was on correct sideband.
has happened on 20 and 10m and maybe others.
The person transmitting might not be using the "correct" sideband.