FCC Initiates Acceptance of Digital FM Sidebands with Asymmetry
FCC Allows Simplified Process for Asymmetric HD Radio Operation
The Federal Communications Commission (FCC) has introduced a streamlined procedure for FM stations to commence asymmetric HD Radio transmission, enabling different digital sideband power levels. This new approach offers broadcasters greater operational flexibility and resource efficiency.
Previously, stations using HD Radio were obliged to run equal IBOC sideband carriers, except if they received experimental or special temporary authority approval.
Advocates argue that this modification will allow stations to optimize HD Radio coverage areas, with the asymmetric nature providing safeguards for adjacent analog stations.
Jeff Detweiler, senior director of business development at Xperi, stated, "This move fosters operational flexibility and promotes swift HD Radio deployments, in addition to providing regulatory clarity." Detweiler also noted that the FCC may adjust the rules in the future based on the influence of digital radio operations on other users.
Stations operating HD Radio between 88.1 and 106.9 MHz can now initiate asymmetric operation by submitting Form 2100, Schedule 335-FM: FM Broadcast Station License Application or Modifications. Upon filing the form, the station may start using asymmetric sidebands and continue unless otherwise notified by the FCC. The notification must include a certification that the digital sideband power levels adhere to authorized power limits.
Xperi spearheaded this push for disparate digital sideband power back in 2011, aiming to authorize voluntary asymmetric digital sideband power. Despite the proposal not leading to immediate action, Xperi, NPR, and NAB renewed their proposal in 2019 regarding the voluntary authorization of asymmetric digital sideband operation.
A recent analysis by Xperi revealed that more than 3,496 FM stations in the U.S. could increase one sideband to -10 dBc, while another 532 could boost one sideband's power to between -14 and -10 dBc. This enhancement is expected to result in increased digital power, even if it falls below the full -10 dBc level.
DBc stands for decibels relative to carrier. Stations transmitting HD Radio digital sidebands at -10 dBc are operating at 10 decibels below the analog FM carrier's ERP (Equivalent Radiated Power), equivalent to 10%. The initial digital power limit was -20 dBc, covering just 1% of the analog ERP. Currently, no station may operate its digital carriers with a total effective radiated power in excess of -10 dBc.
Stations from 107 MHz and above are excluded from the FCC authorization due to concerns raised by the Air Line Pilots Association International about possible interference to navigation systems used by pilots from 108.0 to 117.975 MHz. These stations must seek experimental authorization to transmit IBOC signals with asymmetric power levels.
Stations wishing to file for asymmetric operation should follow the aforementioned step-by-step guidance. Detailed FCC rules and requirements may be found in the FCC’s public notice dated May 23. The FCC welcomes letters to the editor on this or any story at [email protected].
- The new FCC procedure for asymmetric HD Radio transmission allows radio stations to use digital sideband carriers with different power levels, as outlined in Form 2100, Schedule 335-FM: FM Broadcast Station License Application or Modifications.
- Technology advancements in digital radio have enabled broadcasters to optimize HD Radio coverage areas with the asymmetric nature providing protection for adjacent analog stations.
- The FCC's decision to allow asymmetric HD Radio operation is expected to foster operational flexibility and expedite digital radio deployments, according to Jeff Detweiler, senior director of business development at Xperi.
- In the future, the FCC may modify the regulations on digital radio operations based on their impact on other users within the media and finance industries.
