Solder may not be best because there are two dis-similar metals involved and galvanic corrosion and weakening of the solder may take place compromising the junction. All you need is a bit of acid in the soil or acid rain to start that corrosion process. Ref: http://www.corrosion-doctors.org/Forms-galvanic/galvanic-corrosion.htm Use a minimum of 4 gauge copper wire from the mast or tower base to the ground rod using the type of clamps pictured in these next links. INSPECT those clamps and ground wire once per year and replace components as required due to ANY corrosion. Many masts or tower bases have a factory ground attachment location. If your mast or tower does not have a factory supplied area for grounding, make sure that you use 100 grit sandpaper to clean the area as well as the ground rod itself where the claps go. 4 gauge or larger ground wire is available at most Home Depot's in Department 27 (electrical) for roughly a dollar per foot. Please do not use spiral radiator style clamps! There is not sufficient contact area or compression torque to secure ground wires. Grounding Clamps: http://i.ebayimg.com/images/i/261571274156-0-1/s-l1000.jpg OR http://i.ebayimg.com/images/i/170877755197-0-1/s-l1000.jpg Good luck with the project.