How much power does the HD antenna radiate?
1/100 of the station’s licensed analog radiated power. So if you have an ERP of 100 kW you will need an HD transmitter/antenna system with an ERP of 1 kW. If your antenna has a power gain of 5 then your HD transmitter’s output power needs to have only about 200 watts. (200 watts multiplied by 5 equals 1000 watts which is 1 kilowatt.) However, in a high-level combining system, 90% of the digital power is lost to heat, so that means you would need 2 kW at the HD transmitter. (Not considering the loss in power that occurs in the transmission line.) You should also be aware that the high-level combining process steals approximately 10% of the power from your analog transmitter, so if you use high-level combining you need to have the additional analog transmitter power to make up for the loss. Split-level combining solves much of this problem.