Updated March 9, 2017
The FCC only authorizes 50 watts maximum for LP-100 stations located within 125 km of the Mexican border.
This is in accordance with the United States/Mexico Agreement on FM Broadcasting that was drafted prior to the creation of the LPFM service. Even though the agreement does address "LPFM" stations, this also addresses translators. Basically it states that all "LPFM" stations operating within 125 km of the common border with Mexico will be permitted to radiate no more than 50 watts in the direction of Mexico. Since all LPFM stations are non-directional, there is no question that all LPFMs near the border would be affected. One thing to keep in mind about this restriction, it is 50 watts in the direction of Mexico, not 50 watts at 30 meters height above average terrain (HAAT). What this means is for stations that are proposed in this "strip zone" should consider operating at locations above 30m HAAT. If you set up a station at ground level in an area that is 30m HAAT, you will be limited to 50 watts. However, an LPFM station operating at 42m HAAT with 50 watts will be able to achieve a full LPFM service contour. Taking the station to a higher HAAT will lower power but still maintain the full LPFM service contour. Even though a LPFM station in the strip zone is only running at half power, they are currently required to protect other stations (and other LPFMs are required to protect them) as if they are a full LPFM station. REC's myLPFM.com advises users that a proposed location is within the border strip zone.
In addition to the 50 watt cap, LPFM stations within 125 km of Mexico also have the following limitations:
- The 60 dBu protected service contour may not extend more than 8.7 kilometers in the direction of Mexico.
- The 34 dBu interfering contour may not extend more than 32 kilometers in the direction of Mexico. (Note: we have received mixed messages from the FCC regarding the size of this contour. The Mexico Agreement does not specify a field strength for the interfering contour like it does for the protected contour. The translator rules does state that boosters must limit their 34 dBu contours but makes no mention of translators. While we should focus on preventing the 34 dBu contour to extend more than 32 km but if they don't, we may be able to assist if the 40 dBu does not reach 32 km.)
When evaluating these limitations, we look at only the bearings where there is any Mexican territory within 125 km along that azimuth. LPFM stations in the strip zone should get professional services such as from REC to assure that the proposed facility meets the treaty requirements. For bearings that are more than 125 km from the border (as well as stations more than 125km from the border), the 60 dBu contour can not exceed 8.7 km from the point that radial reaches 125 km from the border.
LPFM applicants near Mexico will have a delay as the FCC goes through the Mexican notification process. At a certain point in the process, the FCC will grant the construction permit with a condition that Mexican concurrence is still pending. Construction permits can be tolled (extended) for the length of the overall concurrence process.
So far, no LPFM station from either the 2000/2001 or the 2013 windows has ever been denied as a result of an objection from Mexico.
Reminder about LPFM secondary status
In addition to being secondary to FM broadcast stations in the United States, LPFM is also secondary to foreign FM full power stations. Just like there is a notification process when the US places a station within the border area (within 320km of the border area), Mexico has to do the same. Although we are not aware of it happening yet, a change in Mexican facilities may cause displacement or additional interference.