Put the brown sugar, corn syrup, butter, cream of tartar and salt in a heavy saucepan. Melt over medium heat and bring to a boil. Boil 5 minutes. Remove from heat and add the baking soda. Stir well. Pour over the popped corn and pecans. Stir well. Put in a baking pan and bake at 250~ for 30 minutes, stirring occasionally. Pour onto buttered cookie sheets to cool