for the receiving LNB
This is just for my personal documentation. But the functional principle may be also usable for other purposes.
The LNB's local oscillator usually works on 25 MHz resulting in an output frequency of 740 MHz for the QO-100 transponder.
To avoid an additional down-mixer I have modified the LO frequency to 25,769231 MHz (using the leobodnar GPS). Now the output is on 439,550 MHz (CW beacon) and can be directly received with my 70cm SSB receiver.
Of course, the 14V (or 12V) supply for the LNB is required. Additionally I want to send a 10 MHz reference signal over the RX coaxial cable to my TRX in order to synchronize the transceiver.
The following circuit does this job: