On March 17, 2004, the FCC approved the use of separate analog and digital antennas to initiate HD Radio FM transmissions. Although not required for HD Radio broadcasting, this separate antenna option enables many FM stations to use existing equipment and reduce HD Radio implementation costs. The FCC's decision was based on the recommendation and report filed by the NAB on July 24, 2003. This report included extensive field tests conducted by iBiquity that were specified and witnessed by the NAB. Stations seeking to use a separate antenna implementation must request Special Temporary Authority (“STA”) from the FCC at least 10 days prior to the planned date of commencement of HD Radio™ transmissions. The STA request must demonstrate compliance with the following criteria outlined in the NAB’s recommendation to the FCC:
- The digital transmission must use an auxiliary antenna.
- The auxiliary antenna must be within three seconds of latitude and longitude of the main antenna.
- The height above average terrain of the auxiliary antennas must be between 70 and 100 percent of the height above average terrain of the main antenna.
In addition, the STA request must contain the following information:
- The date that interim operation is planned to commence.
- A certification that the HD Radio™ facilities conform to the iBiquity hybrid specifications.
- The name and telephone number of a technical representative the FCC can contact in the event of interference.
- Transmitter power output for the analog and digital transmitters.
- A certification that analog reflective radiated power remains as authorized.
- A certification that the interim operation would not cause human exposure to levels of radiofrequency radiation in excess of Section 1.1310 of the FCC’s rules and is therefore categorically excluded from environmental processing pursuant to Section 1.1306(b). Any station that cannot certify compliance must submit an environmental assessment (EA) pursuant to Section 1.1311 and may not commence interim operation until such EA is ruled upon by the FCC.
- Geographic coordinates, elevation data, and license file number for the auxiliary antenna to be employed for digital transmissions.
- For systems employing interleaved antenna bays, a certification that adequate filtering and/or isolation equipment has been installed to prevent spurious emissions in excess of the limits specified in 47 C.F.R. Section 73.317.