A B757-200 PLT RPTS A GPWS WARNING ON SHORT FINAL TO TAPA (ST JOHNS; ANTIGUA) WHERE NO OBSTACLE OR ANTENNA IS SHOWN ON CHARTS PRODUCED BY COMMERCIAL COMPANY. TERRAIN MAP ON COCKPIT DISPLAY MOMENTARILY SHOWS OBSTACLE PRESENT.

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DSNDING ON FINAL APCH FOR VOR RWY 7 TO TAPA; WE RECEIVED GPWS INDICATIONS; WARNING AND 'OBSTACLE; OBSTACLE.' WE BOTH SCANNED THE 2 MILES AHEAD OF US FOR ANY OBSTACLE. THE PLT FLYING HAD LEVELED OFF AND ALSO CONFIRMED HE SAW NO OBSTACLE. I AUTHORIZED HIM TO CONTINUE THE VISUAL APCH AND LNDG. WE BOTH LATER INSPECTED THE APCH PLATES AND CHARTS AND COULD DETECT NO CLOSE IN OBSTACLE. UPON DEPARTING; I TRIED TO FIND SOMETHING VISUALLY BUT COULD ONLY SEE A COUPLE OF RADIO ANTENNAS THAT MIGHT BE 200 FT. IS IT POSSIBLE THAT A NEW ANTENNA MIGHT HAVE BEEN INSTALLED ALONG THE APCH PATH AND COMMERCIAL CHART COMPANY NOT BE AWARE OF IT? HAVE ANY OTHER CREWS TO TAPA EXPERIENCED THIS WARNING? COULD THIS BE A PROB DURING AN IFR APCH? LET'S LOOK INTO THIS BEFORE SOMEONE FINDS THE OBSTACLE THE HARD WAY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THIS WAS AN EGPWS EVENT AND THAT THE OBSTACLE DISPLAYED ON THE CAPT'S PFD SINCE GPWS WAS NOT SELECTED FOR DISPLAY. RPTR ADVISED THAT HE RETURNED TO THIS ARPT AND THE SAME EGPWS ALERT OCCURRED AGAIN. RPTR STATED THAT AFTER LNDG AND LOOKING BACK UP THE APCH COURSE; THE CREW WAS ABLE TO IDENTIFY A TOWER AT APPROX 1.5 NM FROM THE RWY. RPTR ESTIMATED THE TOWER WAS 200 - 250 FT. RPTR ADVISED THAT HIS FO ALSO HAD THE SAME EGPWS ALERT EXPERIENCE AT THIS POINT ON PREVIOUS FLTS. ON A SUBSEQUENT CALLBACK; THE RPTR STATED THAT THE ARPT MANAGER NOTIFIED HIM OF A 592 FT MSL TWR AT 1.5 NM FROM THE APCH END OF RWY 7 VERY SLIGHTLY OFF CENTERLINE. RPTR STATED THAT THE ARPT MANAGER ALSO STATED THAT NUMEROUS FLT CREWS HAVE RPTED THE OBSTACLE AND AT LEAST TWO GO-AROUNDS HAVE FOLLOWED THE WARNINGS. RPTR STATED THAT A FOREIGN CARRIER SERVICING THE ARPT DID HAVE THE OBSTACLE DEPICTED ON THEIR PROPRIETARY SOFTWARE AND CHARTS.