MYTH: Full power station makes a modification and is now short spaced to an LPFM meaning that the LPFM station is automatically required to shut down.

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While it is possible in some cases where a full-power station’s modification will result in an LPFM station having to cease operation, the myth culminates from a misunderstanding of the rules around when a full-service station can ask the FCC for the displacement of an LPFM station.

LPFM stations have to meet specific distance separations to full-service stations.  The distances used are calculated by adding the sum of the standard distance of the interfering contour from the LPFM transmitter site to the appropriate interfering contour, the standard distance from the full-service station to the standard service contour (60, 57 or 54 dBu) based on the maximum for its service class and an additional 20 kilometer “buffer zone” between the LPFM interfering contour distance and the full-service service contour distance. 

If a full-power station increases service class and/or changes transmitter location, it may result in an LPFM station that once met the minimum distance separation requirements to no longer meet those distances resulting in a short-spacing.  A new short-spacing in itself does not mean the LPFM station must cease operation although the LPFM station may experience increased interference as a result.  It also means that if the LPFM station makes a subsequent change in transmitter location, they may remain short-spaced as long as the distance of the proposed site is the same or more kilometers away from the full-service station, even if the new site is still short-spaced to the full-service station.  Distances are rounded to the nearest kilometer. 

Rules about the forced displacement of LPFM stations can be found in §73.809 of the rules.  Specifically, it states that subsequent full-service modifications on the same or first-adjacent channels can only result in potential displacement if either:

  1. The appropriate interfering contour of the LPFM station overlaps the 70 dBu community coverage contour of the full-service station; or
  2. The appropriate interfering contour of the LPFM station overlaps the corporate limits of the designated community of license of the full-service station.

This displacement policy does not apply if the full-service station is operating on the second-adjacent channel of the LPFM station.

LPFM displacement is not automatic, it must be requested by the full-service station in the form of a complaint to the FCC.  There is no time limit on when this displacement can be requested therefore LPFM stations that are in this situation should have a plan in the event a complaint is made in the future, especially after the full-service station changes owners or management.

LPFM stations that are subject to interference because of a full-service modification may file to change channels as long as an alternate channel is available and in the case of a second-adjacent channel waiver, is able to demonstrate that there will be no interference to any nearby occupied structures. 

The displacement policy also has a due-process provision where if an LPFM station can demonstrate through technical showings (preferably one that is jointly conducted by the LPFM and the full-service station) that the LPFM station is not the cause of any interference, then the LPFM will be absolved of all interference and will be allowed to continue operating.

FACT: A subsequent modification by a full-service station resulting in a short-spacing does not automatically mean an LPFM station must shut down.  Other factors must be considered and the request to shut down needs to proactively come from the full-service station. 

LPFM's most common myths
Answer Date: 
Sunday, November 12, 2023