Capture effect
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In telecommunication, the capture effect, or FM capture effect, is a phenomenon, associated with FM reception, in which only the stronger of two signals at or near the same frequency will be demodulated.
The capture effect is defined as the complete suppression of the weaker signal occurs at the receiver limiter, if it has one, where it is not amplified, but attenuated. When both signals are nearly equal in strength, or are fading independently, the receiver may switch from one to the other.
Note: AM radio transmission is not subject to this effect. For this reason, the aviation industry and others have chosen to use AM for communications rather than FM, allowing multiple signals to be broadcasted on the same channel.
However, for digital modulation schemes this is not the whole story. It has been shown that for properly implemented OOK/ASK systems, co-channel rejection can be better than for FSK systems.
Source: from Federal Standard 1037C and from MIL-STD-188
