More on LP-250

Sat, 03/31/2012 - 20:07

With REC's recent release of a list of LP-100 stations that we predicted may be eligible for an upgrade to 250 watts, we received a mixed response and I thank you for the feedback. Let's talk about why it seems like we have so many stations that are predicted to be able to upgrade to 250 watts. You may be familiar with the infamous "buffer zone". When the FCC created the LPFM service over a decade ago, they decided to place a "buffer zone" outside a full power station's maximum service contour (based on class), thus giving it a 20 km extension. A LP-100 or LP-10's interference contour could not cross into that buffer zone. The idea of the buffer zone was to allow the full power station to make facility moves and other changes within that 20km buffer with minimal impacts to the LP-100. Section 3(b)(1) of the Local Community Radio Act (LCRA) states:

IN GENERAL- The Federal Communications Commission shall not amend its rules to reduce the minimum co-channel and first- and second-adjacent channel distance separation requirements in effect on the date of enactment of this Act between--

  • (A) low-power FM stations; and (B) full-service FM stations.

The FCC has interpreted that to mean the current power levels in effect at the time the LCRA was passed (LP-10 and LP-100). While the buffer zone is specifically not in the LCRA, language specifying that the distance can't be reduced is. Now let's say that the FCC created an LP-250 service without a buffer zone. If they could, an LP-250 could be as close as 52 km to a full power Class-A station. LP-100 with the buffer zone is 67km. Since that would put the LP-250 at closer spacing than even LP-10, it would be in violation of the LCRA. So what the FCC did was keep the 20km buffer zone but allowed the interference contours of LP-250 stations to cross into the zone. The result was a LP-250 distance spacing chart where on co-channel and first-adjacent channels, the required minimum distance separations between LPFM and full power stations are exactly the same. The only differences are in second adjacent, IF (which is still going to be required for LP-250), translators and foreign stations. As the FCC states, the LP-250 co-channel 34dBu interference contour in respect to a Class B FM station crosses 8.8 km into the buffer zone but still does not cause the LPFM interference contour to overlap the full power station's service contour. This is why many LPFM stations are able to stay at their current locations and still upgrade on their own channel. Stations required to change channels likely became short spaced by subsequent application activity by full power FM stations. LP-250 "psuedo-Buffer Zone" sizes ~ (distance from the edge of the Full Power FM service contour to the edge of the LPFM interference contour):

  • Primary Station is Class B: Co-Channel 11.2km, First-adjacent Channel 17.3km.
  • Primary Station is Class B1: Co-Channel 13.9km, First-adjacent Channel 17.6km.
  • Primary Station is not Class B or B1: Co-Channel 14.8km, First-adjacent channel 17.9km.

There were concerns raised about the LP-250 list REC published on March 30. This list was developed to show the potential for LPFM stations in general to consider upgrading to LP-250. Because the FCC has interpreted the use of contours, especially on co- and first adjacent channels to be a violation of the LCRA, minimum distance spacing for LPFM is here to stay for now. We advise stations that no matter where they are on that list (which was intended only as a prediction) to work with a qualified consulting engineer to verify their current status and work on solutions for maximizing their station. As we mention very frequently, the use of the REC tools are intended for prequalification and do not replace the services of a qualified consulting engineer.