REC Advisory Letter #4: Directional antennas for LPFM stations

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.  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.

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, even if a directional antenna is specified on the LMS application form and appears in the FCC and REC database with tabulations specified.

Even though the FCC has agreed that LPFM stations operating DAs in these two categories are eligible for nondirectional protection from FM translators, they will still appear in all of the public and private sector data sources as a directional facility and therefore, an application could be filed by an FM translator that specifies an interfering contour of the translator that would overlap the service contour of an LPFM station if they were nondirectional. REC is concerned that the Staff may not always catch this since there is nothing positive (that we know of) in their database that indicates the reason why an LPFM station is directional and because of the few instances where this type of situation comes up, it will be a rare occurrence, but one that has the potential to harm LPFM stations in this situation.

LPFM stations that submit modification applications with tabulations on them and where the DA is used solely for second-adjacent channel waivers will need to be more vigilant on the application activity in their area by FM translators proposing a different operation on the LPFM’s channel or first-adjacent channels .FM translators on second or third-adjacent channels are not required to protect LPFM stations.  If a contour study by the LPFM station demonstrates that if the LPFM station is treated as a nondirectional station (by considering all directions at a full 1.000 field value), that there would be contour overlap, then an Informal Objection to the FM translator application is warranted.

REC will do our best to watch the translator application activity to assure that there is no encroachment to these protected directional LPFM stations. But if your LPFM station is on a tabulated directional facility and you suspect that a certain FM translator application may encroach the LPFM station’s nondirectional service contour, they should first contact REC so we can verify that there is contour overlap and then they should contact their attorney to file an Informal Objection against the translator application.  Stations can file their own objections without needing an attorney.  For a modest fee, REC can provide a statement to include in your objection to support the technical findings. 

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.