16. Specifying transmit and receive antennas is perhaps the most difficult task of any HF circuit simulation. And yet antenna type, siting and gain variations can influence prediction integrity more than most other parameters. For this reason, ACE-HF includes several aids to antenna selection. You may select from many antenna models (and antenna array models) in the Inputs Screen. Further optional settings may set in the above panel. The most useful control is the Multi-Channel Antenna Schedule, wherein different transmit antenna types may be specified for up to four band ranges. Different Multi-Channel schedules may be specified for both ends of each circuit. Multi-Channel Antenna Schedules may be saved and recalled as desired. When such schedules are selected, the point-to-point and area coverage computations follow the schedule as predictions at different frequencies are computed. This panel also provides settings for Isotropic Antenna gains, and permits the user to specify a minimum elevation (takeoff) angle for the transmit antenna.