The FM antenna pictured is a shared aperture ERI ROTOTILLER. The array is two antennas, one for the analog signal and one for KNOW-FM’s HD Radio digital signal. The analog antenna is an ERI Model SHP-8AC, eight bay circularly polarized FM antenna and the digital array is an LP-7C. Both antennas are equipped with optional radomes for protection for heavy snow and ice. To enhance isolation between the antennas they are cross polarized, the analog antenna is right hand circular polarization and the HD antenna is left hand CP. Each antenna is fed by it own transmission line. The benefit of using antenna space combining for simulcasting analog and digital IBOC signals is that this approach eliminates combining losses that are present in systems that use high level combining. This approach also uses separate analog and digital FM transmitters which are more efficient than common amplification transmitter systems.
Bill Harland 