What is the transmission line loss for coax?

This depends on the amount, as well as the type of coax used. On the average, 50 feet of RG-58 coax will have about 3dB loss, 50 feet of RG-8X coax will have about 2dB loss, and 50 feet of RG-213 (RG-8U) will have about 1dB loss.