Just started to trace out the 15 Mhz signal internal to the ref1. Top of board side near oven and rs422 connector are the power amplifiers and output on off control for the 15 Mhz. The signal comes from the bottom of the board. J8 is 5 Mhz. So will need to take the board out to trace further. Not looking forward to that task. Regards Paul WB8TSL