Updated April 7, 2020.
When the FCC originally approved LPFM, it made a very controversial move to allow LPFM stations to not be required to protect a domestic full power or translator station's third adjacent channel (+/- 600 kHz). This decision was made based on studies done by a pro-LPFM group, the National Association of Broadcasters (NAB) (which supports third adjacent protection requirements) and a study conducted by the Commission's own Office of Engineering and Technology. The FCC opened up some filing windows and allowed applications without the third adjacent channel protection.
In 2012, the FCC has implemented the rules related to the Local Community Radio Act of 2010 which sets the operating rules for LPFM stations on third adjacent channels.
The Radio Broadcast Protection Act
The NAB which has opposed the LPFM service in general used it's lobbying power to get Congress to include a "rider" on a DC appropriations bill that would impose a third adjacent channel protection to full power and FM translator stations, require distance separation and impose a ban on any person with a "pirate past" from being a party to an LPFM license. As a result of this rider, all applications that did not meet third adjacent channel spacing were automatically void.
The bill also required the FCC to conduct a technical field trial on the impact of LPFM stations operating on third adjacent channels as well as a study on the economic impact that these stations could create.
The Radio Broadcast Protection Act was passed and eventually codified in the FCC rules. The FCC then had a short remedial filing window where those impacted by the RBPA could file a major change application to move their station to a different location and/or channel. Some stations filed applications while others were deadlocked. Those who were deadlocked were dismissed on March 17, 2003, a day we call the "St. Patty's Day Massacre".
The Local Community Radio Act of 2009
As a part of the RBPA, the FCC was required to conduct an independent study on the impact of Low Power FM radio stations operating on third adjacent channels. The report from the FCC's subcontractor, MITRE Corporation showed that there will be minimal impact on full power FM broadcast stations. In 2009, a version of the LCRA was passed by voice vote in the House but died in the Senate.
The Local Community Radio Act of 2010
After negotiation with what some would call a "whole new" National Association of Broadcasters, a 2010 version of the LCRA was introduced and easily passed the House and Senate on voice votes.
Where third-adjacent channel protection rules still apply
- Foreign stations. FM stations in Canada, Mexico and the British Virgin Islands must continue to be protected to the third adjacent channel per existing international agreements.
- Radio Reading Services. Approximately 200 FM radio stations were identified by the FCC in 2001 as those that operate radio reading services for the blind and visually impaired using subcarriers. Since those subcarriers operate are more vulnerable to interference, the third adjacent channel restriction remains in tact for these 200 stations.
- "Input" Channels for Translators. While some FM translators receive their source programming through satellite or microwave, most of them receive their source directly from the primary station or though another translator. The FCC plans to require LPFM stations to protect these FM translators, but not based on the channel that the translator transmits on but based on the channel they receive. The FCC has declared a "translator protection zone". The Translator Protection Zone is a radius of 2 km around the translator. In addition, the Translator Protection Zone extends to 10 km in an area that is located +/- 30 degrees azimuth from the heading between the translator and the source station.
In the example below, we have a translator operating on 92.7 and it is receiving over the air, a source signal from its primary station operating on 95.9 and that primary station is located at a heading of 215º from the translator. The translator protection zone would be:
- All areas within 2 km of the translator.
- In areas within 10 km of the translator that are oriented between 195º and 255º azimuth from the translator.
In this specific case, no LPFM operations would be permitted on 95.9 or 96.5. LPFM applications will have to make a showing that their stations will not cause interference to translator inputs.
On Air Advisory Messages
The FCC has determined that LPFM stations that "satisfy the minimum third-adjacent spacing requirements" for the first year of operation, must carry on-air advisory messages to advise of potential interference.
The FCC clarified the rule regarding LPFM stations operating on third-adjacent channels of full power stations. Under the FCC's clarification, they consider the closest fully spaced third adjacent channel station 3 channels (600 kHz) below and the closest fully spaced third adjacent channel station 3 channels above the proposed LPFM channel would be the subjects to the announcement. You will not be required to announce a third adjacent channel station if it is located more than 100 km from the LPFM station.
If the LPFM station is "short spaced" to the third adjacent channel station, no announcement is required for that station. Short spaced stations are already subject to more stringent interference guidelines.
This functionality is now in myLPFM. The search result will indicate in the channel whether announcements may be required. This can be found by clicking on the channel number in the results after the facility information is built.
During the first 30 days of operation, the LPFM station must broadcast the announcement at least once between the hours of 7AM and 9AM or between the hours of 4PM and 6PM with the second announcement per day being made outside of this period. LPFM stations that do not operate during those periods must make the announcement during the first two hours of the broadcast day. LPFM stations must vary the times the announcements are heard to assure that as many listeners as possible hear it.
During days 31 through 365 of operation, announcements must be broadcast twice a week between 7AM and midnight.
Interference
For information on how third-adjacent channel interference is handled, see Section 73.810 of the FCC Rules.
