1 cup sugar
1 cup water
3 cups grapefruit juice or orange juice (add a squeeze of lemon if using orange)
1/2 cup Campari
Mix the water and sugar together in a small pan over low heat, and bring up to a boil until the sugar dissolves. Allow the simple syrup to boil for 4 minutes, remove from heat. and cool (makes a little over 1 cup of simple syrup).
Combine the citrus juice and Campari and add 1 cup of the cooled syrup. Adjust to taste (for the grapefruit pops, you may want to add a tablespoon or two extra syrup if you prefer them less tart). Remember, the mixture will taste slightly sweeter in liquid form than it does when frozen.
Pour into popsicle molds and freeze at least 8 hours or overnight. To remove, run the molds quickly under hot water, and gently pull out the pops.