Above I mixed the R3361 and R3131 IF frequencies, sorry. The first IF of the R3131 is 4113.58 MHz, not 4066 MHz which is the R3361's.
Hence read:
3 GHz: around 7084 MHz, should be 7113,58 around 29 MHz low
2 GHz: around 6116 MHz, should be 6113,58 around 3 MHz low
1 GHz: around 5146 MHz, should be 5113,58 around 33 MHz high
Renaud