What are the differences between MAX2870 and MAX2871?

It would take too long to give an exhaustive list of differences.  Basically, the MAX2871 is a more recent device that improves performance and adds new features.  To quote the MAX2871 datasheet: "The MAX2871 has an improved feature set and better overall phase noise and is fully pin and software-compatible with the
MAX2870."  One can compare the benefits and features section on the front page of the respective datasheets and observe there are new features such as the ability to phase synchronize multiple synthesizers or automatic VCO selection which exist for the MAX2871 but not MAX2870.  There are various specs such as max PFD frequency or output power level which are improved in MAX2871 vs MAX2870.

It would take too long to give an exhaustive list of differences.  Basically, the MAX2871 is a more recent device that improves performance and adds new features.  To quote the MAX2871 datasheet: "The MAX2871 has an improved feature set and better overall phase noise and is fully pin and software-compatible with the
MAX2870."  One can compare the benefits and features section on the front page of the respective datasheets and observe there are new features such as the ability to phase synchronize multiple synthesizers or automatic VCO selection which exist for the MAX2871 but not MAX2870.  There are various specs such as max PFD frequency or output power level which are improved in MAX2871 vs MAX2870.