REC Advisory Letter #6: Proposed changes to FM Boosters to support "geo-targeting"

This REC Advisory Letter is to advise LPFM licensees of a pending rulemaking proceeding before the FCC.  This is an overview of the proceeding and our initial analysis of the impacts to LPFM and potential positions that will be taken by REC Networks in respect to this proceeding.  As with any proceeding, REC always welcomes the input from LPFM licensees, including those that REC has not worked with in the past to provide input. 

A quick tutorial on FM Boosters

This proposal involves the FM Booster service.  FM Boosters are broadcast transmitters that operate on the same frequency as the primary FM station that they are intended to serve.  An FM Booster is used in order to provide FM service to an area that, based on contours, should be served by the primary FM station but because of terrain or other factors, the primary FM station does not reach that point.  FM Boosters are intended to fill in these gaps.  The 60 dBu service contour of an FM Booster must be fully inside of the 60 dBu service contour of the primary FM station that it serves.  FM Boosters are also limited to an effective radiated power (ERP) of up to 20% of the maximum ERP allowed for the station class of the primary station. 

FM Boosters must carry the same programming as the primary FM station at all times. With the exception of LPFM, a primary station can have as many boosters that are necessary (LPFM is limited to two, counted like translators).  For proper operation, the FM Booster must be built in a manner where the audio from the primary station and the booster(s) is/are synchronized.  This is usually done by inserting a delay at the primary station.   

Unlike other services, FM Booster construction permits can be filed at any time without waiting for a filing window.  Once accepted for filing, there will be a Petition to Deny period just like with any other original construction permit application.

The Notice of Proposed Rulemaking

The original proposal was filed by GeoBroadcast Systems (GBS) and was assigned RM-11854.  There was a comment period on this Petition for Rulemaking in April, 2020. 

Under the proposal, GBS is requesting that FM booster stations be permitted for a short period of time each hour (such as three minutes) to air “geo targeted” content via the booster that would not air on the primary station.  This could include local commercials, local news and weather information.  Under current FCC rules, FM boosters may only broadcast the audio output of the main audio output of the analog FM station for which the booster is affiliated with. 

On December 1, 2020, the FCC had released a Notice of Proposed Rulemaking in MB Docket 20-401.  A comment deadline will be announced once the NPRM is published in the Federal Register. 

“Self-interference” by FM Boosters

Much of the concern in the NPRM is the issue of “self-interference”.  Because the booster operates on the same channel as the primary station and because of the technical nature of frequency modulation emissions, the radio receiver may pick up the signals of both the primary station and the FM Booster.  In cases where one signal is stronger than the other, “capture effect” will cause the strongest signal to be discriminated on the receiver and that is what is heard by the listener.  Questions have been raised in respect to potential increased interference to other stations.  The FCC is also inquiring about concerns raised by REC that adding this new functionality to FM Boosters will increase the number of booster facilities on the air.

How FM Boosters protect other facilities

Since FM Boosters are limited to the area within the 60 dBu service contour of their primary station, there are very few rules regarding interference.  FM Boosters are only required to provide specific protections to first-adjacent channel facilities (both primary and previously authorized secondary stations) and for FM Boosters that operate with more than 99 watts ERP, protection to the intermediate frequencies (+/- 53/54 channels).  This means that there are no required protections to other facilities on co-, second- or third-adjacent channels.  FM Boosters in border areas are subject to the same international agreements that apply to FM Translators.

FM Boosters are subject to the same interference remediation rules that apply to FM Translators.  These rules were recently changed in 2018 require a “package” of listener complaints that meet specific technical requirements and the magnitude of complaints vary based on the population within the 60 dBu contour of the interfered-with station.  Complaints can come from any point within the interfering station’s 45 dBu service contour.

How other stations protect FM Boosters

Since FM Boosters must reside solely within the 60 dBu service contour of their primary station, the booster’s 60 dBu service contour will be protected by FM translators because the interfering contour of the FM Translator can’t overlap the service contour of the primary station. 

LPFM stations protect primary full-service stations through a distance separation method that is based on the “standard” service contour size of the full-service station plus a 20 kilometer buffer zone.  Because of this, LPFM stations are not required to provide any specific contour-based protection to boosters.  In some cases where the LPFM station is in a foothill location and has a larger service contour in a particular direction, there is a possibility of overlap into both the primary station’s and the FM Booster station’s service contour.  Rules specifically state that full-service FM stations may receive interference from LPFM stations that meet the distance separation criteria.

REC Threat Level – LOW TO MEDIUM

REC’s position is that the threat level of this petition is currently “low to medium” as long as the FCC does not modify any technical rules.  The current rules have existed in some form since the early 1970s and in the 20 years of the LPFM service, REC has not been made aware of any interference to LPFM stations by an FM Booster that was activated subsequent to the LPFM operation.  Without any modifications to the technical rules, this change is nothing more than just the ability to change program content through ad-insertion technology.

REC has already expressed concerns to the FCC that this proposal may encourage a “booster boom”, where companies like GBS could market FM Boosters as an advertising tool and stations that did not consider boosters before may now want to consider them.  It is important to remember that FM Boosters only work in certain situations where the primary station can’t be heard too strong.  This will further limit the ability for stations to place boosters.

There is another proposal, RM-11854, that would allow fill-in FM Translators and FM Boosters to extend their service contour to the primary station’s 45 dBu contour.  This proposal has been considered an “extremely high” threat to LPFM.  RM-11858 is currently not being considered by the FCC.

REC positions on this proposal

The audio chain aspect of the service can provide a smaller number of full-service commercial, NCE and even LPFM stations the ability to split programming and for stations in the noncommercial sector, allow for different underwriting acknowledgement announcements to air on the booster (such as to acknowledge support for the booster).  We only support split audio for a short period of time each hour.  We do have concerns on how this concept will interact with forwarded EAS alerts. 

To avoid a “booster boom”, the Commission can look at a requirement for FM Boosters to protect co-channel LPFM, FM Translators and even full-service FM stations.  This will reduce the number of interference packages by affected stations against new boosters.  REC opposes the FCC inquiry of whether second-adjacent channel protections from FM Boosters be added.  There is no need for it and is incompatible with REC policy that second-adjacent channel interference is a rare phenomena and that consideration for de minimis population within the interference overlap zones should be permitted for FM Translators and LPFM stations (the latter may require amendment of the Local Community Radio Act unless the FCC feels that they are empowered to define “interference”). 

What do LPFM stations have to do?

For most LPFM stations, this may never become an issue.  For LPFM stations that are on co-channels with full-service stations inside of their interfering contour and that station has an area of their service contour where the full-service station can’t be heard because of terrain, they should be prepared to be move vigilant of any booster application activity as of right now, since applications for FM Boosters are always being accepted by the FCC. 

Final thoughts

This NPRM has bipartisan support on the FCC (O’Reilly, Carr and Starks) and may likely happen.  We have not heard an opinion yet from Rosenworcel on this proposal but she may side with Starks.  No matter which party has majority on the FCC, we see this NPRM reaching fruition in some form or another.

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For more information

For legal questions, please contact your attorney.  For other questions including information not construed as legal advice, please contact REC Networks. 


This Advisory Letter may contain some interpretations and positions that have either not been reviewed by a qualified attorney nor tested in case law.  This document does not replace the services of a qualified attorney and therefore does not construe legal advice.  Only a qualified attorney can provide legal advice.

Originally written on December 2, 2020.

Michelle Bradley, CBT at REC Networks.

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