CPB is planning a station survey to determine the extent of a problem that has crept up practically unnoticed during planning for the DTV transition: what pubcasters can or should do with old analog equipment. Some stations are simply letting the equipment sit while they ponder its fate. But that can take a huge amount of space: Many analog TV transmitters are the size of three refrigerators in a row, accompanied by a high-voltage power supply nearly as big. The obsolete analog antennas, still perched in the sky, add weight to aging towers that threaten to topple on equipment below. Selling all this outdated stuff poses its own complications, including federal liens, university property-disposal rules and the glut of retired hardware that has few buyers.