Part 73, Subpart G, Section 73.827 is a complex rule that addresses interference by LPFM stations to the "input" channels of FM translators.
Interference to the input of an FM translator
FM translator stations are intended to rebroadcast the signals of a full-service FM station to another area. Some translators are used to rebroadcast the signal of an AM radio station and others are used to rebroadcast the HD subchannels (HD2, HD3 or HD4) of a full-service FM stations allowing these HD subchannels to be heard on an analog FM radio that does not include HD Radio functionality.
Many FM translators are required to receive the full-service FM station directly over the air or through another FM translator over the air. The frequency that the FM translator receives their source signal is referred to as their "input channel".
An LPFM station that is located at a distance from the primary FM station far enough to make the distance separation requirements may still interfere with a FM translator trying to receive the primary station. This rule addresses those situations.
Third-adjacent input channel interference
Section 6 of the Local Community Radio Act of 2010 requires that the FCC establishes standards to address interference to FM translator inputs by LPFM stations operating on the third-adjacent channel of the input channel that the FM translator is monitoring. The rule states that an LPFM station will not be authorized if on a third-adjacent channel, there is an input channel for an FM translator and the LPFM station is located either within 2 kilometers (1.24 miles) of the FM translator in any direction or within 10 kilometers (6.21 miles) of a translator when the LPFM station is located in the "path" between the FM translator and the station it is monitoring. This is done by determining the bearing (direction) of the path from the FM translator to the station it is monitoring and then protecting the radii within 30 degrees in either direction. An LPFM station proposing operation in this "potential interference area" may need to be prepared to make a technical study that shows that no interference takes place. The rule provides three different technical methods to demonstrate a lack of interference.
Other input channel interference
The rule also includes a basic policy that an LPFM station may not interfere with the input frequency of a FM translator as long as the translator was carrying the impacted primary station before the time when the FCC announced a filing window for new LPFM stations (the last being in 2013).
LPFM stations that are notified of interference will need to shut down immediately, but can make short test transmissions to test the efficacy of remedial efforts made by the LPFM station. The complaining FM translator must cooperate with the LPFM station in these remedial tests, otherwise the LPFM station will be absolved of any further responsibility for the complaint.
Regulatory history
This rule was created in the 2000 Order on Reconsideration with the "other input channel interference" policy shown above. In the 2012 Sixth Report and Order, the rule was amended to implement Section 6 of the LCRA to address interference to translator inputs on third-adjacent channels. In 2013, in the Sixth Order on Reconsideration, additional language was added to acknowledge that some translators do not receive their input signal from the ultimate primary station, but instead from another translator (this is also known as "daisy chaning"). The 2013 reconsideration order also clarified that the translator is only protected if had the same primary station relationship at the time when the FCC announced the LPFM filing window.
Federal Register citation
78 FR 2106, Jan. 9, 2013, as amended at 78 FR 67317, Nov. 12, 2013
Text of regulation 47 CFR §73.827
§ 73.827 Interference to the input signals of FM translator or FM booster stations.
(a) Interference to the direct reception of the input signal of an FM translator station. This subsection applies when an LPFM application proposes to operate near an FM translator station, the FM translator station is receiving its input signal off-air (either directly from the primary station or from a translator station) and the LPFM application proposes to operate on a third-adjacent channel to the station delivering an input signal to the translator station. In these circumstances, the LPFM station will not be authorized unless it is located at least 2 km from the FM translator station. In addition, in cases where an LPFM station is located within ±30 degrees of the azimuth between the FM translator station and its input signal, the LPFM station will not be authorized unless it is located at least 10 kilometers from the FM translator station. The provisions of this subsection will not apply if the LPFM applicant:
(1) Demonstrates that no actual interference will occur due to an undesired (LPFM) to desired (station delivering signal to translator station) ratio below 34 dB at such translator station's receive antenna.
(2) Complies with the minimum LPFM/FM translator distance separation calculated in accordance with the following formula: du = 133.5 antilog [(Peu + Gru − Grd − Ed)/20], where du = the minimum allowed separation in km, Peu = LPFM ERP in dBW, Gru = gain (dBd) of the FM translator receive antenna in the direction of the LPFM site, Grd = gain (dBd) of the FM translator receive antenna in the direction of the primary station site, Ed = predicted field strength (dBu) of the primary station at the translator site, or
(3) Reaches an agreement with the licensee of the FM translator regarding an alternative technical solution.
Note to paragraph (a):
LPFM applicants may assume that an FM translator station's receive and transmit antennas are collocated.
(b) An authorized LPFM station will not be permitted to continue to operate if an FM translator or FM booster station demonstrates that the LPFM station is causing actual interference to the FM translator or FM booster station's input signal, provided that the same input signal was in use or proposed in an application filed with the Commission prior to the release of the public notice announcing the dates for an LPFM application filing window and has been continuously in use or proposed since that time.
(c) Complaints of actual interference by an LPFM station subject to paragraph (b) of this section must be served on the LPFM licensee and the Federal Communications Commission, Attention: Audio Division, Media Bureau. The LPFM station must suspend operations upon the receipt of such complaint unless the interference has been resolved to the satisfaction of the complainant on the basis of suitable techniques. Short test transmissions may be made during the period of suspended operations to check the efficacy of remedial measures. An LPFM station may only resume full operation at the direction of the Federal Communications Commission. If the Commission determines that the complainant has refused to permit the LPFM station to apply remedial techniques that demonstrably will eliminate the interference without impairment of the original reception, the licensee of the LPFM station is absolved of further responsibility for the complaint.