REC Advisory Letter #6: FM Boosters and GeoTargeting

Updated May 29, 2024

Recent rule changes at the FCC now permit broadcast stations that operate FM booster stations to be able to apply technology that will permit the programming on the booster to be different than what is carried on the primary station for no more than 3 minutes per hour.  This is also known as "geo-targeting" or by the Geo Broadcast Solutions' (GBS) trade name "ZoneCasting".  As of May 16, 2024, interim rules have been put into place by the FCC that permits such operation after obtaining an experimental authorization under Part 5 of the Rules. There is no requirement to use the GBS specific technology.  A Further Notice of Rulemaking is currently under consideration by the FCC that would put a more permanent process in place where geo-targeted operations will be permitted as long as a notification is made to the FCC.  The final rules regarding these notifications are still being worked out in the NPRM.

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.

“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 (but only after the booster construction has been completed).  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.

How will this impact existing LPFM stations?

Full-service stations not subsequently modified after the LPFM facility placement

For LPFM stations that meet the minimum distance separation requirements to a full-service station with FM boosters, the potential impacts may be fairly low, as long as the full-service station has not made any subsequent modifications to move closer to the LPFM station.

Full-service stations that have modified since the LPFM facility placement

The substantial impact to LPFM may occur in situations where, at the time the LPFM application was filed for the current location, that it met all distance separation requirements but then subsequent to that, the full-service FM station filed a modification of their facility to either physically move closer towards the LPFM station, upgrade in power, or both.  Even if those modifications did not result in a significant increase in overall interfererence towards the LPFM station, especially where certain factors such as intervening terrain are taken into consideration. 

The concern is that since the service contour of the full-service station may be closer to the LPFM now, a full-service station may file to place an FM booster in that area.  While the service contour of the booster must remain within the service contour of the primary station, the interfering contour of the booster may encroach upon the protected service contour of the LPFM station, which could result in harmful interference to the LPFM in a portion of its service area. 

Like LPFM, FM boosters are also considered a secondary service.  The Local Community Radio Act also states that LPFM stations, FM translators and FM boosters are "equal" in status.

The current FM booster rules, last revised in the early 1980s only have protection requirements for first-adjacent channels, not for co-channel.  The FCC does currently apply the interference rule §74.1203 to FM booosters the same way that it does to FM translators.  This includes co-channel.  The problem with this rule is that the booster must be constructed and on the air first before an interference complaint can be filed. Unlike FM translators, §74.1204(f), which can address potential interference pre-construction do not apply, nor is there an up-front protection rule that can stop an application from being filed in the first place.

In the Further Notice of Proposed Rulemaking, the FCC has proposed that §74.1204(f) also apply to FM boosters.  REC agrees with that position.  However, REC is also calling upon the FCC to amend §74.1204(i) to include an up-front protection ratio requirement for FM boosters on co-channel as it does on first-adjacent channels in order to protect the large number of LPFM and FM translator stations that have been established since the early 80s.  

What do LPFM stations have to do?

As of May 29, 2024, we are not aware of any experimental requests filed by FM boosters.  There have only been a very small number of construction permit applications filed for new FM boosters in 2024.   We strongly suggest at this time that you check your station's current situation in respect to other full-service FM facilities on the same channel.  REC clients with a minimum $350 historical spend can use the Encroachment Report in myLPFM to get a look at how any full-service station interferes with the LPFM station.  Once the full-service station is noted, please keep a watch for application activitiy by watching or periodically returning to the Encroachment Report in myLPFM.

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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.

First Revision on May 29, 2024.

Michelle Bradley, CBT at REC Networks.

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