REC Advisory Letter #4: Directional antennas for LPFM stations

Updated May 24, 2021 to reflect clarification on application handling for directional antennas for the sole purpose of travelers information stations and second adjcent channel waivers based on a consultation with FCC staff.

On October 30, 2020, Part 73 of the rules was amended to expand the use of directional antennas in the LPFM radio service.  With the new rules, LPFM stations may elect to use a directional antenna (DA) for any purpose, where in the past, it was limited to two specific reasons, public sector traveler’s information services (TIS) and solely for second adjacent channel protection.

LPFM stations desiring to use a directional antenna for purposes other than TIS, second adjacent channel waivers and in order to meet an international agreement will be required to file additional steps at the time of licensing the directional facility. This includes the need for a proof of performance document, which confirms how the directional antenna will perform.  This can usually be obtained by the antenna manufacturer.  In addition, license applications must include a statement from a licensed surveyor or other person in a similar capacity to verify that the antenna was properly installed at the appropriate height and heading. 

LPFM stations desiring directional facilities after October 30, 2020 will now be required to specify their directional antenna details on the LMS application form unless the sole reason for the directional antenna is for a travelers' information station by a qualified public safety entity or solely for a second adjacent channel waiver.  This is done through specifying a directional facility and entering in the field values (also known as tabulations) for 36 different points in the directional pattern.  Those field values are provided by your antenna’s manufacturer.  These field values will appear in the FCC database, REC’s databases and in the software used by consultants and engineers like V-Soft and ComStudy 2 and will create contours that corresponds with those entered field values.

LPFM stations seeking to use a directional antenna for the purpose of providing a travelers' information station (the licensee must be a qualified government public safety agency or a non-government organizaiton with specific "jurisdiction", such as providing police or fire services in an area under contract, compact or covenant) or for the sole purpose of demonstrating compliance with the second-adjacent channel waiver rules, will continue to use the "non-directional" option on the LMS application.  Public safety applicants will be able to construct with the directional antenna.  Second adjacent waiver applicants should point out in their construction permit application how the antenna will assure that no interference is caused to any occupied areas.

Protection to other radio stations.

It is important to realize that the use of directional antennas by LPFM stations does not afford the right of the LPFM station to move the station closer than the minimum distance separation requirements shown in §73.807 of the rules.  This includes full-service, FM translators and other LPFM stations. 

Protection to TV Channel 6 stations.

A directional antenna’s pattern can be taken into consideration when the request is for an LPFM station wishing to use a reserved band (88.1~91.9) channel and the station does not meet the §73.825 minimum distance separation to a full-service or low power television station.  In those cases, an LPFM station will be permitted to use the translator Channel 6 contour protection criteria outlined in §74.1205 and request a waiver to §73.825. If this method is used, you must also send a notification to the affected Channel 6 station(s).  Concurrence from the Channel 6 station is not required however if you are able to get a concurrence letter from the affected Channel 6 station prior to filing, you will be able to include that letter in lieu of meeting any distance separation requirements or needing a contour study.  You may be able to negotiate a nondirectional antenna proposal with the affected Channel 6 station if they are willing to provide a concurrence letter. 

Protection from FM translators

Normally, a directional station is protected from other stations based on their service contour as modified through the use of the directional antenna.  There are some exceptions when the protected station is an LPFM.

On November 9, 2020, after consultation with FCC Staff, REC has confirmed that the FCC will continue to honor the note in §74.1204(a)(4) and a decision made in the Sixth Report and Order where LPFM stations utilizing a DA for the sole purpose of a TIS or for second-adjacent channel waiver will be protected as a nondirectional antenna. Based on a separate consulation with FCC staff in May, 2021, the application is still written as a nondirectional facility, thus not requiring the entry of tabulations on the form.  As mentioned, second adjacent waivers will need to demonstrate how the directional antenna will assure compliance.

Applications for directional antennas for the purpose of Mexico or Candian compliance, Channel 6 protection or for any other purpose must be written with "directional" selected and include tabulations.  Translators will protect based on the directional facilities.

Dispelling the big myth about DAs

Despite what some may tell you, using a DA will not give an LPFM station “more range”. For most, especially from the amateur radio and hobbyist community think of transmitter power, which is used in ham radio and not necessarily effective radiated power (ERP), which is used in broadcasting.  A directional antenna may provide more gain than other antenna types, however, ERP is based on power at the antenna as opposed to power at the transmitter.  Any time a higher gain antenna is installed, this means that in order to meet your authorized ERP at the antenna, the power output of the transmitter would have to be reduced to compensate.  If anything, a DA will result in you losing areas that you may otherwise be entitled to and not gain anything new.

DAs in LPFM are rare

As REC has stated in the past, DA usage in the LPFM service is rare and should only be for specific purposes such as:

  • Stations operated by a city or state government that provides traveler’s information services.
  • LPFM stations needing to use a DA to prevent a second-adjacent channel interfering contour from reaching occupied structures.
  • LPFM stations within 125 km of the Mexican border using a DA to limit the ERP in the direction of Mexico to 50 watts or less while getting up to 100 watts in the other directions.
  • LPFM stations near the Mexican or Canadian border with a terrain advantage needing to use a DA to limit radiation towards the other country in accordance with the international agreements.
  • LPFM stations operating on reserved band channels that are outside the 47 dBu contours of Channel 6 stations but must use a DA in order to prevent their interfering contour from overlapping.

For assistance, please contact REC Networks at 202 621-2355.

References