Interesting stuff. and quite understand the wandering of an carrier from a unstable rig so glad had mine checked out other year by very good local chap. Radio certainly seemed better afterwards. Mind does wander 1kz at times but keep close eye on the read out LED.
But surely if your not controlling your modulation say with an non standard mike to stick with in the lower part of the as in LSB and carrier its expands above the freq to which you are using and if not into USB part of the carrier as QRM.
I have been floating around 40m to day and even The Belgium Sota was heard 2kz above his freq mind you was strong signal from him. But do note not clearly as on freq but still heard.
I will be keeping eye out for an local Inter course would like to go for it and hopefully this summer time may be one of the local clubs do one.
Mind you mine is an early 80’s Trio 120V with stand mike and again will not take risk operating next to the border as so to speak. But look forwards to day get me pennies together and get hold of a nice FT450D I will be seeking one day soon.
These 120v good rigs but bit of a noise box.
Again gent thanks for the input on this one