Thanks, guys; I've chased the links. The HR Smith site isn't very useful, however, other than a contact address.
Blade antennas on the top of tri-jets are a special case, as they have to be heated to keep ice accumulations from being shed and into the big Hoover on the tail. Artex is recommending mounting the antenna to the side of the #2 engine, certainly not a good compromise, but there appears to be no heated tri-band antenna available.
GB