Thanks Bill. That sounds like a productive route to follow. I will have to do some digging to find out about this 'gdb' thing. Never heard of it, so this will provide a new interest to get me through the dark time of the winter... :))) I am a linux beginner so I am constantly coming up against issues, one way or another. 

I will also re-start wsjtx in a terminal window. I've seen error messages when I was having trouble with GQRX. I've had a variety of problems before this, but managed to solve them easily enough. I almost always have to use the 'killall wsjtx' command to unlock the program after it has stopped, because when it falls over, it doesn't do so tidily and leaves some resource or other tied up with the dead instance of the program.

73s - and thanks for your input. I'll come back if that's OK and tell you what happened...

de G0BZB - OP Tony