"Bobby" wrote in message
...

So, from where the ground-wave local signal fades out, to where the
skywave signal first shows up, is the gap, with poor reception of the
station's signal. Clearly Atlantic City, NJ, is in the gap for NYC
clear channels.

Not exactly true. The "gap" is actually the cancellation zone where the
skywave and the groundwave come in, but at enough of a time difference to
cause effects commonly thought of as fading, fluttering, etc.