What was found
ON TAKEOFF ROLL, GPWS 'PULL UP' SQUAWKED SEVERAL TIMES, CAPT REPORTED SPEED UNDER 60 KNOTS. PULLED OFF TO DEFER (34-29A) AND SILENCE GPWS COMPUTER. MAINTENANCE VERIFIED BAD RADIO ALTIMETER ANTENNA. REPLACED ANTENNA, OPS CHECK GOOD. RETURNED A/C TO SERVICE.