The ELINT birds were full spectrum snoopers. They could monitor and record just about every form of electromagnetic emision generated in their assigned area. Everything from broadcast radio and TV, all kinds of communications, microwave, navigation, radar, IFF, remote control signals, missile steering signals, you name it, they got it on tape. They carried linguists, cryptographers, communications specialists, intelligence analysts and spooks of all stripes onboard, and could record just about any event in real time. Needless to say, they could track and record MiGs as they intercepted strike forces, and by listening on aircraft frequencies, could hear them being vectored for attack runs. They knew which bases the MiGs were coming from by their communications long before they could see them on radar.