Wolfgang, i use the same type of octagon, but only the board, i cut off the horn. It is modified for external ref input 25,......Mc to lock on GPS. I cutted one of the 2 F-conn tracks on the board, and with a dc blocking cap the ref sig is going in, workes FB. Also using Bodnar dual gpsdo with 10mhz and between 25-26mhz outputs. Look for G4JNT mods on lnb.