Another lesson for me: I should also read the entire thread before responding!Marcy, the carrier you hear on 279 kHz is most likely from NDB CQX, at Chatham Airport on Cape Cod. I hear this regularly. Its Morse IDs are +/1 1.02 kHz from that carrier, but I can usually hear the LSB one better than the upper one. I've actually been out to Chatham Airport and have seen the antenna for CQX NDB - don't have precise measurements but it's two tall poles holding up a multi-wire horizontal top hat capacitance array, fed from below. Too much poison ivy and a threatening chain link fence had me keeping my distance.
A good rule of thumb is if you hear a carrier precisely on an integer kHz between 200 kHz and 520 kHz, it's very likely an NDB somewhere. There are a few exceptions for LW broadcasters, of course, such as 225 Poland, 253 Algeria, etc., but not so many compared to NDBs in that frequency range. Here's a good link to a great NDB list:
www.dxinfocentre.com/ndb.htm
(also look at the parent page for a lot of other useful lists)
73, Bruce WA1HGJ