Section §73.215 of the FCC rules was first created in 1989. In the original Report and Order, the FCC summarized it as "rules that permit an applicant for a commercial FM broadcast station to request the authorization of a transmitter site that would be nominally short-spaced to other co-channel or adjacent channel stations, provided the service of those other licensees is protected from interference in accordance with well established criteria. The maximum amount of short-spacing is limited by the amount of separation specified for the next smaller size station class."
How full-service FM stations protect each other
In the non-reserved portion of the band, the primary method for protection between two full-service FM stations is through distance separation. Distances are based on maximum facilities for each service class and are based adding the distance to the interfering contour of the incumbent station class with the service (protected) contour of the proposed station class and then vice versa and using the higher of the two values to determine the minimum separation. The use of distance separation is also used in LPFM but the manner of reaching the minimum and recommended values is different.
Full-service stations are required to be spaced from other full-service stations on co-, first-, second- and third-adjacent channels as well as on intermediate frequencies (+/- 53 or 54 channels, 10.6 or 10.8 MHz). A table showing these separations can be found in the rules in section §73.207.
Another rule, §73.213 covers a small number of Class A FM stations that were authorized prior to November 16, 1964 that are otherwise short-spaced to other stations.
Finally, full-service commercial stations have the option of using §73.215 to propose a different site or higher service class where they would otherwise be short-spaced for that service class. This is done in cases where the short-spaced FM station may not be operating at the maximum power and HAAT combination for their station class.
NOTE: §73.215 relates to FM stations operating in the non-reserved (channels 221~300, 92.1~107.9 MHz) portion of the band and that is where the scope of this discussion will take place. In the reserved band (channels 201~220, 88.1~91.9 MHz), full-service FM stations use contour overlap to protect each other and have different technical rules related to directional antennas than commercial stations do. We also note that we may use the term "commercial full-service" throughout this document to generally refer to any full-service FM broadcast station operating in the non-reserved band including non-commercial educational FM stations operating on non-reserved channels as they are also subject to the "commercial" technical rules.
A quick primer on FM station classes
As we covered in the Class C4 Fact Sheet, the FCC has divided the country into "zones". Class A stations are available in all zones, Class B and B1 stations are available only in Zones I and I-A and Classes C3, C2, C1, C0 and C are available only in Zone II. The proposed Class C4 will only be available in Zone II.
This chart is a listing of these service classes and their basic maximum parameters:
| FM Station Class | Reference Power (ERP) | Reference Height (HAAT) | Protected contour field strength | Distance to the protected service contour |
|---|---|---|---|---|
| A | 6 kW | 100m | 60 dBu | 28.3 km |
| Proposed C4 | 12 kW | 100m | 60 dBu | 33.3 km |
| C3 | 25 kW | 100m | 60 dBu | 39.1 km |
| B1 | 25 kW | 100m | 57 dBu | 44.7 km |
| C2 | 50 kW | 150m | 60 dBu | 52.2 km |
| B | 50 kW | 150m | 54 dBu | 65.1 km |
| C1 | 100 kW | 299m | 60 dBu | 72.3 km |
| C0 | 100 kW | 450m | 60 dBu | 83.4 km |
| C | 100 kW | 600m | 60 dBu | 91.8 km |
How §73.215 currently works
When a commercial FM station proposes a short-spacing with another commercial station, the two stations must still meet a minimum distance separation but that required separation (shown in §73.215) is less than the normal separation (shown in §73.207).
Next, for the station that is being short-spaced, a calculation based on the station's power (ERP) and height above average terrain (HAAT) must be done to determine if their actual service contour is the class maximum (see the last column in the table above). If it is not, then the ERP and HAAT may need to be adjusted so it is calculated at that height and power, even if the adjusted height would be physically impossible to achieve otherwise.
Then, a contour overlap study is conducted by first taking the interfering contour of the proposed facility and the protected service contour of the incumbent facility based on that facility's parameters that we adjusted in the previous step. Then, we do the opposite by taking the service contour of the proposed facility and the interfering contour of the incumbent station as adjusted in the previous step.
If a contour study can demonstrate no overlap and the lower minimum separations are met, then it may be possible to short-space the station using §73.215.
Directional antennas in commercial FM
In order to achieve a short-spacing using §73.215, it may be necessary to use a directional antenna. Those who follow LPFM topics may be very aware of the types of antennas used with FM translators and they can sometimes be very directional by directing virtually all power in one direction while "nulling" out other areas. The commercial FM rules do allow for directional antennas but not the highly directional variety you see in the translator world.
In the commercial FM world, directional antennas cannot propose a pattern that would result in more than a 15 dB maximum to minimum radiation. For example, for an upgraded Class C4 station running 12 kW ERP, they must operate a minimum of 380 watts (0.38 kW) in all directions (this also applies to full-service FM stations in the reserved band). In addition, there is an additional rule that requires directional antennas in commercial FM used for §73.215 to also limit their pattern to a manner where the difference in radiation is no more than 2 dB for every 10 degrees of azimuth. For example, the chart and graph below shows a "worst case scenario" of what a directional antenna nulled in one direction could look like. Of course, it is possible to reduce power in multiple directions but this is how the 15 dB and 2dB rule look if they are taken to their maximums in one direction:
It is important to realize in the commercial world, if these kinds of non-standard "composite" patterns are used, it extensively increases the expense for the full-service station to have a custom antenna designed. In addition, the FCC requires full-service directional antennas to provide proof of performance statements when covering construction permits to demonstrate that the antenna was built to standard as well as a statement from a certified surveyor stating that the antenna was built at the correct location and is oriented in the correct direction. While these rules technically also exist for FM translators, they are not enforced. We also note that the FCC does charge higher filing fees to process commercial FM applications involving directional antennas.
Therefore, for a commercial station, especially a smaller mom-and-pop station, a directional antenna can be a very expensive proposition.
An upgrade using §73.215 in action (using today's rules)
Let's say the FCC allows for the new Class C4 service (and denies the proposed changes in §73.215 which will discuss in a bit). Let's take a rural station KPGG in Ashdown, AR, just a bit north of Texarkana. This is currently a Class A station operating at full facilities (5.1 kW at 108m HAAT). This station currently meets §73.207 minimum spacing with all stations. Let's say this station wants to upgrade to Class C4. The upgrade would result in three short-spacings:
CHANNEL: 280 - CLASS: C4
CHAN FREQ CALL LOCATION CLS DIST REQ CLEAR BEAR
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280 103.9 KMHT-FM MARSHALL TX A 117.9 132.0 -14.1 192.4
: HANSZEN BROADCAST GROUP, INC.
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281 104.1 KENA-FM HATFIELD AR C2 106.7 111.0 -4.3 348.6
: OUACHITA BROADCASTING, INC.
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282 104.3 KPOS FOUKE AR A 35.2 37.0 -1.8 142.2
: EDUCATIONAL MEDIA FOUNDATION
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Since no official §73.215 distances have been proposed by the FCC yet, we will assume that the this facility would meet all three short-spacings as §73.215 is based in part on the distance to the lower class.
KMHT-FM is a Class A co-channel station currently authorized at 1.85 kW at 129 meters HAAT which comes out to a 24.3 km service contour which is well below a full Class A facility of 28.3 km.
KENA-FM is a Class C2 first-adjacent station currently authorized at 28.5 kW at 143m HAAT which comes out to a 46.2 km service contour which is also well below a full Class C2 facility of 52.2 km.
KPOS is a class A second-adjacent channel station currently authorized at 5 kW at 110m HAAT which comes out to a 28.3 km service contour which is a full facility.
For the purpose of determining protection under the current §73.215 rule, we will increase KMHT's power from 1.85 kW ot 3.7 kW. For KENA, we will have to increase the height by 7 meters and increase the ERP to 50 kW in order to achieve the full facility. No adjustments to KPOS are required.
With KPGG as a full non-directional C4 facility, we would have contour overlap from KPIG's 40 dBu interfering contour into KMHT's protected contour as well as KENA's interfering contour coming slightly into KPGG's service contour. The protected contour of KPOS is well outside of the 100 dBu contour of KPGG and therefore is not a factor at Class C4.
This would mean that under the current §73.215 rule, KPGG would need a composite directional antenna that will protect both KMHT to the south and KENA to the north.
KPGG can also propose operation at 7.4 kW non-directional and only need to protect KMHT with a directional antenna.
What changes with the current proposal?
The Notice of Inquiry issued by the FCC proposes a major change to how §73.215 is handled. As mentioned, protections to incumbent stations that are currently not at full facilities for their station class will be protected based on hypothetical maximum facilities based on their station class even if an actual physical facility with that configuration is physically impossible (think of it as building hypothetical towers at unheard-of heights).
Under the proposal, if the incumbent facility has been using their currently licensed site for at least 10 years, then contour protection would be based on the actual facility as opposed to the maximum hypothetical facility as in today's rules.
The thought is that by using actual facilities, class upgrades can be achieved easier with less need for complex directional antennas and can be seen as a more efficient use of spectrum.
Let's go back to the KPGG example
As we pointed out in the KPGG example, both KMHT and KENA are running at less than full facilities and both of those stations have been running those facilities for at least 10 years. Under the proposed plan, instead of using hypothetical full facilities for protection, the actual facilities will be used. Remember, the mentality here is that the incumbent station has had over a decade to upgrade these facilities to something closer to the class maximum and they have not, so they should not have to be protected to the class maximum if that spectrum could be used for another station to upgrade.
In the case of KPGG, they can either specify operation at 10.5 kW with a directional antenna slightly protecting KMHT to the south (which could possibly be achieved through their existing side mounted antenna or they can operate non-directional at 8.3 kW ERP (that would be an increase from 5.1 kW).
How will this proposal impact LPFM?
Before we discuss this, let's try to prevent some confusion before it happens. While the Class C4 aspect of the Notice of Inquiry is intended for Class A stations in Zone II, the §73.215 proposal is for all commercial FM service classes in all zones.
Since this method of handling §73.215 is available in any situation where it would otherwise meet the 10 year minimum facility, existing §73.215 distance separation rules and can achieve contour protection based on less than class maximum power and/or a directional antenna based on the current rules, it has the ability to increase the class of many commercial FM stations.
A class increase could put an LPFM station into a situation where they will become §73.807 short spaced and unable to move in certain directions. The class and eventual power increase will also raise the noise floor around the station thus meaning the LPFM is likely to experience increased interference in some of or in all the areas served by the LPFM station.
This will also increase the possibility of an LPFM station causing interfernce under §73.809 of the rules which could result in displacement. This is most likely to happen where an LPFM is currently short spaced to a subsequently authorized full service FM station and that station increases class thus resulting in the interfering contour of the LPFM station overlapping with the 70 dBu city grade contour of the upgrading full-service FM station. If the full-service station complains of interference in this case, it is considered actionable and will result in a request by the FCC to shut down within 3 hours.
NAB and iHeart Media opposes the §73.215 aspect of this inquiry because they know that it will hurt the FM translators even worse than it will impact LPFM.
REC also fully opposes the change to the §73.215 rules on the grounds of increased interference to LPFM and FM translator stations (including the new cross-service translators) and we would question whether increasing class on higher powered FM stations meets the 47 USC §307(b) mandate of a fair, efficent and equitable distribution of radio services.
How does the LCRA play into the §73.215 proposal?
We do note that it is very likely that the comments that will come from some with cross-service (AM) translators will advocate that their specific translators be protected from upgraded stations using the new §73.215 criteria thus suggesting a "primary" or "protected" status for specific types of translators. Any atttempt to change the status of specific types of FM translators (or all FM translators) would be direct contravention of Section 5(3) of the LCRA (the "equal in status" clause). The FCC has already suggested in the Notice of Inquiry that they may be reluctant to adopt any proposal that would have a significantly negative impact on FM translators and LPFM stations.
We must fight the §73.215 aspect of this Notice of Inquiry.
