The left hand pcb accepts the 9.5GHz local oscillator from an external multiplier unit . It is a dual pupose pcb and is labelled 12/24 GHz but here it doubles to 19Ghz. Its output is coupled by wave guide milled into the rear of the box to the 38GHz multiplier. This is again waveguide coupled to the mixer board, lower right of centre. The mixer employs an anti-parallel diode pair (HP) which doubles the 38GHz LO to 76GHz in the mixing process. The receive signal circular waveguide is again on the reverse side. The top PCB contains both the IF amplifier and PSU for the local oscillator. The large preset pot sets the transmit IF (145MHz) mixer drive level. The two blue pots optimise the LO drive in the Rx and Tx states for optimum signal conversion.