Hey:

My crystal balls are saying:

Multipath where a reflected signal from the source
is being cancelled out in the zone sort of like
standing waves. It's like waves in a bath tub
they bounce of the sides and produce more inter-
ference waves, and so on. Or FM broadcast stations
signal in the big city with tall buildings, all of a sudden
the signal just goes puff while you're driving along down-
town.

I'd say gits your antenna near a window or put up an
outdoor antenna.

73 OM

n8zu