Hello Yvan,
Indeed, putting foam over the quartz is a far better solution. Looking at the foam that is over the crystals in my 2004 unit, I suspect it was done at the factory.
Meanwhile I improved the stability a lot by mounting a TCXO-9 reference oscillator in the FT847.
I wanted to add my TCXO mod to the files on this group but apparently I'm not aloud to do so.
