73.875
Part 73, Subpart G, Section 73.875 is a regulation in the LPFM service that addresses modifications to the transmission system.
In general, transmissions from an LPFM station must follow standards of good engineering practice and quality to prevent the emission of signals outside of the authorized channel or to exceed established equipment performance measurements.
Changes requiring a granted construction permit
Station modifications that require a granted construction permit and followed up with a license to cover application include:
- Construction of a new tower structure for broadcast purposes except for exact replacements at the same height and geographic coordinates.
- Any changes in geographic coordinates (LPFM does not have a "3 second rule" like full-service broadcasting does).
- The move to a different tower site, even at the same geographic coordinates.
- Any change in antenna height on the same tower that exceeds 2 meters (6 feet) above or 4 meters (12 feet) below the authorized radiation center height above ground.
Changes only requiring a modification of license
Technical modifications
These changes can be made without first getting authorization from the FCC. If these changes are made, then within 10 days, the LPFM station needs to file a Modification of License with the FCC:
- Replacement of the antenna with the same or a different model including a change in the number of antenna bays (elements) as long as the radiation center of the replacement antenna is within 2 meters (6 feet) above and 4 meters (12 feet) below the authorized height above ground.
- Changes to the transmission line (coax cable) even if it is a different type or value.
In both of those cases, the LPFM station must broadcast at its authorized effective radiated power (ERP). A calculation will need to be done to determine the new transmitter power output (TPO) based on the insertion loss of the feedline, the gain or loss of the antenna and the target ERP. The modification of license form will ask for the updated TPO as well as the antenna make, model, number of bays (called "sections" on the form) and the spacing between the bays. Spacing is the wavelengths between the bays. The most common spacing used in multi-bay antennas is:
- 1.0 - Full wave spacing
- 0.9 - 0.9 wave spacing
- 0.85 - 0.85 wave spacing
- 0.5 - Half-wave spacing
For single bay antennas, enter the spacing a 0.1 in LMS to pass the edits on the form.
In those cases, additional studies may be required for FM antennas on or near AM broadcast towers.
Changes in time sharing hours
A modification of license is also used when stations in a time share agreement agree to change their hours. All stations in the time share group should file a Modification of License and attach a copy of the signed time share agreement.
Regulatory history
This rule was enacted in the initial 2000 LPFM Report and Order and has not been amended since. In 2013, the rule was amended in a proceeding An Inquiry Into The Commission's Policies and Rules Regarding AM Radio Service Directional Antenna Performance Verification, Third Report and Order which addressed the move of the "AM Tower Rule" to Part 1, Subpart BB of the rules which deals with construction of FM antennas on or near the towers for AM broadcast stations.
Federal Register citation
65 FR 7640, Feb. 15, 2000, as amended at 78 FR 66298, Nov. 5, 2013
Text of regulation §73.875
§ 73.875 Modification of transmission systems.
The following procedures and restrictions apply to licensee modifications of authorized broadcast transmission system facilities.
(a) The following changes are prohibited:
(1) Those that would result in the emission of signals outside of the authorized channel exceeding limits prescribed for the class of service.
(2) Those that would cause the transmission system to exceed the equipment performance measurements prescribed in § 73.508.
(b) The following changes may be made only after the grant of a construction permit application on FCC Form 318.
(1) Any construction of a new tower structure for broadcast purposes, except for replacement of an existing tower with a new tower of identical height and geographic coordinates.
(2) Any change in station geographic coordinates, including coordinate corrections and any move of the antenna to another tower structure located at the same coordinates.
(3) Any change in antenna height more than 2 meters above or 4 meters below the authorized value.
(4) Any change in channel.
(c) The following LPFM modifications may be made without prior authorization from the Commission. A modification of license application (FCC Form 319) must be submitted to the Commission within 10 days of commencing program test operations pursuant to § 73.1620. For applications filed pursuant to paragraph (c)(1) of this section, the modification of license application must contain an exhibit demonstrating compliance with the Commission's radiofrequency radiation guidelines. In addition, for applications filed solely pursuant to paragraphs (c)(1) or (2) of this section, where the installation is on or near an AM tower, as defined in § 1.30002, an exhibit demonstrating compliance with § 1.30003 or § 1.30002, as applicable, is also required.
(1) Replacement of an antenna with one of the same or different number of antenna bays, provided that the height of the antenna radiation center is not more than 2 meters above or 4 meters below the authorized values. Program test operations at the full authorized ERP may commence immediately upon installation pursuant to § 73.1620(a)(1).
(2) Replacement of a transmission line with one of a different type or length which changes the transmitter operating power (TPO) from the authorized value, but not the ERP, must be reported in a license modification application to the Commission.
(3) Changes in the hours of operation of stations authorized pursuant to time-share agreements in accordance with § 73.872.