I've never seen an Anti-Helicopter mine before, how do they work?
Vietnamese did some fine work in this area during the war, improvised methods when the down draft of the chopper blades. The charges would be in a daisy chain. Not much find when making an air assault into an LZ you thought was secure.
The first generation of improvised types used all sorts of wind vanes and and maybe horizontal pressure panels - as webereod said using the down draft of the rotor blades.
Speaking of Vietnam it is an interesting side story that the USSR developed back then a multi barrel rocket launcher in 30mm caliber named "Kolos" which was basically a shot gun firing a salvo of rockets. Good they decided not to produce these for Vietnam.
Interesting the info about "Kolos", was it a sort of Russian variant of "Fliegerfaust" ?
Regards
stecol