Are translators required to protect LPFM stations?

Yes, translators are required to protect LPFM (Low Power FM) stations. The protection requirements for translators vary depending on the location of the translator and the LPFM station. Here are the key points:

1. Co-Channel Protection: Translators must protect co-channel LPFM stations from interference. This means they should not cause harmful interference to LPFM stations broadcasting on the same frequency (channel).
2. First-Adjacent and Second-Adjacent Channel Protection: Translators must also protect LPFM stations on first-adjacent and second-adjacent channels. This involves ensuring that the translator’s signal does not cause interference to LPFM stations operating on these nearby frequencies.
3. Distance Separation: The protection of LPFM stations by translators is primarily based on distance separation requirements outlined in §73.807 of the FCC rules. These requirements specify minimum distances that must be maintained between the translator and LPFM stations to prevent interference.
4. Non-Common Ownership: Translators that are not commonly owned by the same organization as the LPFM station they rebroadcast must also adhere to these interference protection rules.

In summary, translators are subject to FCC regulations that require them to protect LPFM stations from interference, just as they must protect full-power FM stations and other broadcast services. These protection measures help ensure that all stations can operate without significant interference in their respective coverage areas.

FM translator stations are mandated to safeguard LPFM stations in line with §74.1204(a)(4) of the regulations. Specific protection requirements are also outlined for FM boosters concerning LPFM (as well as other stations) situated on the immediately adjacent channels.

To comprehend these protective measures, a brief tutorial on contours is in order:

Every broadcasting station (be it full power, LPFM, or translator) possesses a safeguarded contour (sometimes referred to as the “service contour”). For LPFM and translators, this contour is established using the 60 dBu contour based on the F(50, 50) curves chart. If an LPFM station operates at 100 watts and is optimally positioned 30 meters above the average terrain on a flat surface, this contour will encompass a radius of 5.6 kilometers, utilizing a non-directional antenna. The service contour is designed to estimate the station’s service area where consistent reception can be anticipated.

Each broadcasting station also features interfering contours. The dimensions of these contours fluctuate based on the proximity of the channel concerning the other station under evaluation. The interference contour for co-channel scenarios is significantly larger than that of the first and second/third adjacent channels. Interfering contours are determined using the F(50, 10) curves chart. The primary purpose of the interference contour is to establish the geographical area in which the “undesired” signal from another facility might impede the anticipated service area of the desired station (the service contour mentioned earlier).

Calculating the distance to each curve involves assessing the height above average terrain (HAAT) across up to 360 different directions (radials). The determined HAAT for a specific direction and the effective radiated power in that same direction (accounting for potential reductions due to directional antennas) are used to ascertain the station’s distance from the calculated chart-based distance. All these data points are interconnected, forming a contour plot.

For instance, in this particular scenario, data points are positioned at 10-degree intervals (36 points), subsequently connected by lines to form the service contour. Consultants typically utilize either 72 points or, if the software permits, a comprehensive 360 points.

For the purpose of ensuring interference-free operation, it is imperative that the interfering contour of the unwanted station does not intersect with the protected (service) contour of the desired station.

Applying this principle to the safeguarding of LPFM stations by translators:

1. FM translators on the same channel (co-channel) that apply for authorization subsequent to the LPFM station cannot be located in a manner where their 40 dBu interfering contour overlaps with the LPFM’s protected contour.
2. FM translators on first-adjacent channels that apply for authorization subsequent to the LPFM station cannot be situated in a way that results in their 54 dBu interference contour overlapping with the LPFM’s protected contour.
3. FM translators on the second and third adjacent channels are not obligated to safeguard LPFM stations.

In the case of LPFM stations that have not yet obtained their operational license (license to cover is pending), they are considered to operate at the maximum allowable facilities (100 watts at 30 meters HAAT). Once the LPFM station’s license is fully approved, the actual operational specifications must be considered. Therefore, if the LPFM station operates at a height below 30 meters HAAT and utilizes less than 100 watts (for instance, due to compliance with a second adjacent channel waiver as per the US-Mexico agreement or station preference), the same level of protection it received during the construction permit phase is not guaranteed.

LPFM stations employing a directional antenna solely for second-adjacent channel waiver reasons or for the service of public safety entities (state, county, and city traveler’s information service) will be protected as if they were using a nondirectional antenna, notwithstanding the presence of a directional antenna on record. In situations where translator applicants fail to recognize this and file for coverage overlapping the hypothetical nondirectional contour of the LPFM station, it becomes necessary to submit an Informal Objection against the translator application.

For LPFM stations using a directional antenna due to international agreements, Channel 6 protection, or any other rationale, protection will only extend to the translator’s directional service contour rather than a hypothetical nondirectional service contour. This allows translators to be situated closer to LPFM stations.

Moreover, it’s important to note that during the computation of the contours, all HAAT measurements below 30 meters are rounded up to 30 meters.

LPFM stations ensure the protection of FM translators on co-channel, first-adjacent, and second-adjacent channels through the utilization of the minimum distance separation criteria outlined in §73.807(a) of the regulations. Additionally, LPFM stations have the option to employ second-adjacent channel waivers, similar to the provisions applicable to full-power stations.