"Ash Wyllie" wrote in
:

Maybe if we put mode C Transponders on every mountain top... And radio
tower for that matter.

Actually, that proposal was not too far off the mark. One suggestion for
ADS-B is to do just that - put a "squirter" (transmit only) on tall
antennas and other non-obvious obstructions. Total cost in parts is about
$30 (plus the money for FAA/FCC certification G). Operating power is
very low, so the long term cost to the operator of a tall transmitting
tower should be much less than the current required strobe light.

jmk