Tony:
The 53131A had three options for the channel 3 input, 3GHz, 5GHz, and 12GHz.
I have never seen anything on EBAY over 3GHz installed in a unit.
I have seen Chinese Channel 3 boards for 3GHz (a lot of them) and 6GHz (just 1) currently listed.
I do not see the 12GHz board listed at this time, although it was listed in the past.
I did a board a few years back using the HMC432 (divide by 2) and two HMC434 (divide by 8) that could get to 6GHz or higher.
A less expensive version would use the HMC432 driving an MC12079 programmed to divide by 64, have the layout for it but never made it.
Never did any follow up on these because the Chinese clone boards were so inexpensive it was not worth pursuing.
ed
