When both signals are nearly equal in strength or are fading independently, the receiver may rapidly switch from one to another and exhibit flutter.
The capture effect phenomenon was first documented in 1938 by General Electric engineers conducting test transmissions.
Two experimental FM stations, located 15 miles (24 km) apart in Albany and Schenectady, New York, were configured to transmit on the same frequency, in order to study how this would affect reception.
The capture effect thus allowed co-channel FM broadcasting stations to be located somewhat closer to each other than AM ones, without causing mutual interference.
The capture effect is actively employed in Europe for aeronautical VHF-communication in the band 118 MHz to 137 MHz to provide coverage for aircraft flying under ATC (Air Traffic Control) in large ATC sectors that cannot be covered by a single transmitter site.
Operation of ILS-Localizer and ILS-Glide-Path at airports is often impossible due to strong reflections, e.g. on terrain and buildings.