REC files comments in support of improvements to HD Radio
REC Networks has filed comments in MB Docket 22-405. The FCC requested comments on two Petitions for Rulemaking. One was filed by the National Association of Broadcasters and Xperi, the owner of the HD Radio technology to change the guidelines for digital effective radiated power (ERP) on stations running HD that are nearby other facilities on first-adjacent channels. The second petition was filed by NAB, Xperi and National Public Radio to request that the FCC normalize the use of "asynchronous sideband" operation by stations operating HD Radio.
How Digital ERP is determined
Stations that operate HD Radio have transmitters that operate a separate digital service at an ERP lower that that of the analog service. This is due to the nature of digital service. When HD Radio was first created, stations were able to operate -20 dBc, or 20 dB below carrier. This meant that their digital ERP was 1 percent of their analog power. Over time, the FCC would permit higher levels. The FCC eventually permitted stations to operate up to -14 dBc or 4 percent of the analog ERP. The FCC permits operation of up to -10 dBc or 10 percent of the analog ERP if the HD Radio facility meets specific contour overlap requirements to nearby FM stations on first-adjacent channels. In order to operate at the full -10 dBc, the 49.6 dBu interfering contour of the HD station cannot reach the first adjacent channel station's 60 dBu service contour. If there is overlap, then a tiered system is used to determine allowable digital power. -10 dBc produces a digital signal that best replicates most of the analog service area. The 60 dBu and related interfering contours are used for this, even if at least one of the stations involved is a Class B1 or B station with a larger protected service contour.
HD Radio inserts two "sideband" signals, one on each side of the analog carrier, therefore one sideband towards the lower channel and one towards the upper channel. Using the current policies, if a HD station needs to protect a first-adjacent channel station on one side, they are required to reduce digital power on both the lower and upper sidebands. The FCC has permitted for several years now, the ability for HD stations to operate in an "asynchronous" manner where the reduced digital ERP is only on the sideband closer to the impacted first-adjacent channel station and full (-10 dBc) power on the sideband not affected by a first-adjacent channel station. This type of operation was considered experimental and required special temporary authority (STA) from the FCC.
Super power stations
Also, when the FCC put the policies in place to permit digital ERP at greater than -20 dBc, they also required that FM facilities that were authorized prior to 1962 with analog ERPs greater than those that would be allowed today within their service class to limit their digital ERP to either -20 dBc or up to -10 dBc based on the ERP that would be allowed today based on the station's height above average terrain (HAAT). For example, at 928 meters HAAT, the maximum ERP for a Class B station today is 0.8 kW (800 watts). Let's say the station is grandparented at 65 kW (65,000 watts). One percent of 65,000 watts is 650 watts (at -20 dBc) and 10 percent of 800 watts is 80 dBc. This would mean that a grandparented super power Class B station operating 65 kW at 928 meters HAAT would be limited to a digital ERP of 650 watts, even though 6,500 watts would be allowed if the station was differently situated and in a different service class.
The NAB/Xperi proposal would request that power reductions to the -10 dBc maximum would not take place unless there is an overlap between the 54 dBu interfering contour of the HD station with the 60 dBu contour of the affected first-adjacent channel station. Gradual power reductions would take place based on how much overlap there is between the two stations down to the -14 dBc minimum that is allowed today for most stations. Their proposal also suggests that this new policy would also applied to "grandfathered super power" stations.
The NAB/Xperi/NPR proposal would eliminate the "experimental" status of doing asynchronous sideband operation and allow for such operation without first obtaining an STA and only requiring a notification similar to how HD Radio is deployed today.
NAB, Xperi and NPR included extensive technical documentation to back up most of what they are proposing.
REC has reviewed both petitions and we do support these proposals in part to reduce the interfering contours needed to protect first-adjacent channel operations and to allow for routine asynchronous sideband operation.
REC did take issue to the proposal to extend these power levels to the grandparented super-power stations. When these stations were grandparented in 1962, there was discussion on whether to require these stations to reduce their power to meet their service classes, that reduction never happened. Instead, the FCC instead stated that while a station can operate at a super-power, their actual protections may be limited to their class maximum (such as only being protected as an 800-watt station despite operating 65,000 watts as outlined in our example above). This is intended to assure that super-power stations do not stunt the growth and development of the FM broadcast service.
REC also expressed concerns about the potential of increased interference/"noise" to some stations that may be close to HD stations on first-adjacent channels. While REC had received reports of such noise in the past, they were very few and have been very isolated. It is our position that the improvement of HD Radio, which can provide a broadcaster (LPFM, NCE or commercial) with an opportunity to provide additional channels of diverse programming through multicasting has a substantial public interest benefit and is consistent with our efforts to keep radio relevant, especially in the face of competition from "non-broadcast" services.
Reply comments in MB Docket 22-405 are due by February 13, 2023.