Razvan:
The 3GHz board is a divide by 128, with a max output of 23.4375MHz at 3GHz.
That has to get to the main board through the ribbon cable, not the best way to connect.
At 12GHz the output would be almost 100MHz so I think that the higher frequency option boards likely have an additional divider to keep the output at a reasonable frequency.
There are two pins (CH3CODE0 and CH3CODE1) on the connector that are used to tell the main board that one of the options is installed.
I would think that a combination of those pins would select one of the three options or no option.
I will try to see what effect they have later this weekend.
ed
