[Myrddin]

FM requires a stronger signal to achieve "full quieting". In the FM world, the strongest station always "wins" by capturing the receiver. AM signals can co-exist at very weak levels. That is why aircraft communications use AM. You can hear strong and weak signals at the same time. The advent of software defined radio allows application of digital filters and demodulators that are superior to what an all RF hardware solution can achieve.

[vortigern]

Agreed. Software-defined radios (SDR) combine traditional analog radio techniques with modern digital signal processing (DSP) capabilities. These specialized techniques are fairly common in professional-grade radio receivers.