.....Although it really benefits the coverage of an FM signal to be in mono with the durabilty of being able to listen much further without noise, most of my radios give me the option to listen in Mono anyway if I need to. Also some radios like car radios and the radio in my Sony Ericsson mobile narrow down their stereo seperation progressively as the signal gets worse so that in a distant spot even though the stereo light might still be on, you will effectively only be hearing mono.
Apparently good reception of
FM Stereo requires a signal that is up to ten times the strength needed for a good FM Mono signal.
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Any FM stations still broadcasting in Mono? - Radio - Digital Spy Forums