How do I figure out which lighting protector I need?

It usually depends on the frequency you are using.
If you're using 900MHz, you will use LP-901
If you're using 2.4GHz or 5GHz, you will typically use LP-25001
There is exceptions when using 2.4GHz and 5GHz so make sure you verify with technical support
You can reach them at 661-716-5100 or via e-mail at [email protected]