The 389 core is larger, and threaded for 50 turns instead of 10. -----Original Message----- From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Jon Schlegel Sent: Thursday, April 30, 2009 2:09 PM How similar is the 389 PTO to the 390 PTO? Would it be possible to do some sort of mix n match? Jon Schlegel WA3MVM