After we did the project, I got to working with the  spectrum analyzer and discovered we could reduce the losses even more by going to 4 turns/28 turns total. (improved design) That gets the losses considerably lower.   For higher power operation, consider one or two FT– 240 Dash 43 toroids ,3 turns/21 turns.   These will not have the capacitive adjustment that the commercial units have, but they will work quite well.  I’ve gotten a look inside some commercial units and they are designed very similarly. 

Gordon Kx4z