I stumbled across a nice BCB modulator.
I re-drew the layout using my own program, with a mod to put in 2 or more x-tals to switch wavelength. 99% of the parts are availabele in my "junk"box.
I also try to build the coupling to the radio on the same board, using a transformer and a input connector and a output plug to plug directly into my car radio (1967 type Blaupunkt MW-LW only)
When switching the thing on also a sort of auto switch to disconnect the antenna.
(is there still someone listening to AM-BCB in a car today??,...eeuh, yeah, me!)
Here the url: