What is the primary function of an external earth connection or ground rod?

The main purpose of an external earth connection or ground rod at an amateur station is to provide lightning protection and to dissipate static electrical charges. When lightning strikes near or directly on an antenna system, a proper ground rod gives that massive electrical charge a direct, low-impedance path into the earth. Ground rods do not effectively reduce RF current flow between pieces of equipment in the shack because the length of the wire connecting the equipment to the ground rod can act as an antenna or inductor at RF frequencies. For RF grounding, bonding the equipment chassis together with short, wide straps is much more effective.