Preparing for HD and Booster Rule Changes

How recent and upcoming rule changes will impact LPFM stations.

As the industry finds new ways to make sure that radio remains relevant, the regulations we all must follow must keep up. Sometimes when there are changes in other parts of the FCC broadcast rules, they can have an impact on the LPFM service. There was one adopted rule change and two more that are coming up that LPFM stations need to be aware of.

HD Radio Asymmetric Operation

The HD Radio technology, also known as “In-Band On Channel” (IBOC) inserts a digital signal that rides along with the analog signal. The digital signal is actually two redundant carriers that ride just outside of the bandwidth needed for analog FM service but still within the confines of the 200 kHz wide channel.

In the early days of HD Radio, the digital signal that is injected would be 20 dB below carrier (normally abbreviated as -20dBc). At -20dBc, the digital effective radiated power (ERP) is 1 percent of the analog ERP. Most stations are now authorized to operate with up to -14dBc, which equates to 4 percent of the analog ERP and upon a technical showing, stations can operate with an injection as high as -10dBc, which is 10 percent of the analog ERP. There are also intermediate steps at -13, -12 and -11 dBc.

To operate at the higher digital ERPs, a technical study needs to show that there would be no interference to first-adjacent channel stations. This is done through a contour study. Of course, since most stations in HD are full-service facilities, they can ignore the presence of LPFM and FM translators as these stations are secondary. This is why sometimes when you hear about an LPFM station getting “HD noise” on their channel, this is normally caused by a first-adjacent channel station running HD.

Under the previous rules, HD stations wanting to run at ERPs stronger than -14 dBc had to look at the contour overlap on both first adjacent channels. If there is contour overlap on one channel but not on the other, then the station was limited to HD operation at the lower digital ERP on both the “lower sideband” (in respect to one channel lower) and “upper sideband” (one channel higher).

Xperi, the company that owns the HD Radio technology had been experimenting with the ability for stations to operate with “asymmetric” ERPs. Thus meaning that the digital power on one sideband is higher on one side band than the other sideband. This way, stations with contour overlap, let’s say on the lower sideband, would have to run at the lower ERP on that sideband while being able to run at a higher power on the upper sideband. There have been several stations that have been testing this on experimental authorizations.

With the rules that were recently adopted, the FCC has “standardized” the asymmetric mode of operation on 88.1~106.9, thus meaning that it would no longer require an experimental authorization.

While the number of full-service FM stations with this kind of first-adjacent channel overlap is fairly small in comparison to all full-service FM stations on the air, there will not be a huge flood of existing or new HD operations that will be running massive digital power on one of their sidebands.

LPFM stations, especially those that are currently §73.807 short-spaced on first-adjacent channel to a full-service station with HD would be the most impacted by this change. At this time, due to concerns raised by the aviation industry, asymmetric operation without an experimental authorization is limited to FM stations operating on 88.1~106.9. Until more testing and evaluation is done, the ability for this type of operation on 107.1~107.9 without experimental authority may take place in the future. REC only sees a minor impact to LPFM stations due to the limited number of stations that would be in a situation where they could resort to asymmetric operation.

LPFM stations that are running HD and are limited due to first-adjacent channel contour overlap will be able to take advantage of the asymmetric operation rules. Unlike full-service, LPFM stations must also consider FM translators and other LPFM stations on first-adjacent channels when determining digital ERP.

FM Booster Rule Changes

As we spoke at great length in a previous article, the FCC is going to be voting on new rules that would remove the experimental status from FM boosters being used for up to three minutes per hour of local insertion as part of a Petition for Rulemaking that was filed by Geo Broadcast Solutions in order to allow for this type of technology.

FM boosters are normally used to fill in “gaps” in the coverage of an FM station within their service contour due to obstructions such as terrain. REC was concerned that this novel utilization of boosters would create a “booster boom” that would motivate stations to obtain boosters in areas that already receive usable service from the existing FM station. Not only would an increase in the number of boosters create potential issues for the listeners of those FM stations, but they could create, in some cases, new interference to secondary services like FM translators and LPFM.

For LPFM, in most cases, the addition of new FM boosters will not create any new interference. However, there is a risk of new interference in cases where after the LPFM (or translator), application activity by either an existing FM station or a new FM station (such as those from the recent Auction 109 and 2021 NCE Filing Window) was to place a facility close enough to the LPFM station on co-channel or first-adjacent channel where the LPFM/translator would experience increased incoming interference.

By rule, LPFM stations already substantially overprotect full-service FM stations on the same or first-adjacent channels because of the additional 20 kilometer “buffer zone” that is added to the minimum distance calculations in §73.807. This buffer zone further reduces the risk in many cases.

FM boosters currently have a rule where they must protect other facilities on first-adjacent channels. A similar “up front” protection requirement does not exist for co-channel. The rule that is used for the remediation of interference by subsequently authorized and constructed FM translators (§74.1203) also applies to FM boosters. However, the other translator interference remediation rule (§74.1204(f)) which can be applied after an application is filed currently does not apply to FM boosters.

In this rulemaking proceeding, REC asked for both an “up front” co-channel protection requirement where the 40 dBu interfering contour of an FM booster cannot overlap the 60 dBu service contour of an existing facility, either primary or secondary, and an extension of the §74.1204(f) regulatory policy to also include FM boosters.

While we were not successful in getting a new “up front” rule added, it appears that we will be getting a rule change that extends §74.1204(f) to also include FM boosters. This means that if a co-channel or first-adjacent channel FM booster is applied for subsequent to the authorization of the existing LPFM or FM translator station, the same interference remediation rules that we use right now to fight a new or modified FM translator facility will also apply to new and modified FM boosters.

While this rule change could add some expense to a small number of LPFM and FM translator stations facing encroachment, at least we no longer have to wait until the booster is constructed and on the air before we can fight it.

Overall, this aspect of the geotargeted FM booster proceeding has a significant benefit to LPFM stations as it allows LPFM stations facing valid interference to be able to speak up sooner in the process instead of having to lose sleep and worry about how the booster is going to impact the LPFM station.

Redefinition of HD Radio Protection Requirements

In the proceeding mentioned above that authorized asymmetric HD operation without an experimental authorization, the FCC held back on the other half of this proceeding that would redefine the interfering contours needed to allow stations running HD Radio to upgrade their power. This has been referred to in the trade press as the “HD Power Boost”.

This proceeding also has the potential for digital power increases for short spaced grandparented “super power” Class B FM stations. Most of these super power stations are in California as well as in other parts of the country where Class B stations are available, including WIPR-FM in Puerto Rico. Currently, these stations are limited to either -20dBc (1%) of their super-powered ERP or -14dBc of what their ERP would be at their height above average terrain if they were not a grandfathered station.

The potential impact to existing LPFM stations from FM stations that are not of the super-power variety is fairly limited, similar to the impacts caused by the asymmetric HD rule changes mentioned above. However, there is more of a cause for concern if the super-powered stations are allowed to take a significant increase in their digital ERP. This would impact LPFM stations that are located inside the interfering contour of the super-powered FM station that is on their co- or first-adjacent channel. On co-channel, it could increase the risk of “HD hijack”, a term coined by REC to describe the effect where the sidebands of the HD signal from a distant station are so high that the HD “takes over” the radio thus replacing the local LPFM station with the distant FM signal. (In all fairness, the potential of HD hijack is also possible from stations that are not grandparented super-power.)

These new rules for super power as well as the redefinition of the contours are not yet in effect as they are still being evaluated by the FCC. There is currently no known timeline on when this rule will be voted on, but I wanted to give everyone a head’s up that it is out there.

As always, if you have questions, feel free to check with REC.