What is a "foothill station" and why is REC proposing additional restrictions on them?


REC defines a "foothill station" as a low-power or full-power station that has a service contour, which in any one of 360 directions, extends a service contour that is the equivilient of 10 dB above the reference power and height above average terrain for that service.  

The terrain on the earth is not perfectly flat.  As a result, some areas are higher in elevation than others.  LPFM determines a maximum ERP by determining the HAAT of a particular location.  HAAT is determined by taking drawing lines in 8 equal directions (45 degrees, 90 degrees, etc.) and then taking the area that is between 3 km and 16 km from the transmitters along those lines and determining the elevation at 50 equally spaced points.  The elevations along each radial are averaged together and then the averages of all 8 radials are averaged together to determine HAAT.  

If an LPFM station's HAAT exceeds 30 meters, then the power must be reduced in order to meet the reference service contour of 5.6 km for LP-100 or 7.1 km for LP-250.  

Because terrain is not flat, a service contour may extend past the reference contour distances above and in cases where the HAAT exceeds 30 meters, may be less than those distances. 

An LPFM station located in the foothills has a huge advantage because despite the higher location over the populated area in front of it, there is much higher elevation behind it.  This means that the high elevations of the mountain range and the low elevations of the valley will average out.  Here's an example of a foothill location in the San Fernando Valley of California at an elevation of 342 meters above sea level:

  • 0 degrees: -229.5m
  • 45 degrees: -253.3m
  • 90 degrees: 23.9m
  • 135 degrees: 101.1m
  • 180 degrees: 49.5m
  • 225 degrees: 12.2m
  • 270 degrees: -18.7m
  • 315 degrees: -290.2m

As a result, the HAAT at ground level for this location is -76 meters despite being as much as 101.1 meters (over 300 feet) above the average terrain on the 135 degree radial.  Since the HAAT calculation for this site is below 30m, a full 100 or 250 watts is allowed.  The distance to the service contour is measured by taking the power of the station and the HAAT in that particular direction and calculating the curve.  All HAAT calculations that are less than 30m will be considered as 30m for the calculation of the contour size.  

Based on that method and the HAAT data above, while the service contour for an LP-250 station in most directions is the standard 7.1 km, along the 135 degree radial, the LPFM station is effectively 250 watts at 101.1m HAAT.  This produces a service contour that extends out to 12.9 km, which is well beyond the 7.1 km standard contour. 

Since REC has defnied a "foothill station" as one with a contour that extends to 10 dB above the reference power levels, this means that the distance can be computed of either one of two ways:

  • The 50 dBu F(50, 50) contour of 100 or 250 watts at 30 meters HAAT, or
  • The 60 dBu F(50, 50) contour at 10-times the power at 30 meters HAAT.

Both ways will come out as 10.2 km for LP-100 and 12.7 km for LP-250. 

In the above example, since the LP-250 service contour extends to 12.9 km in one direction, this means that the station's location has a considerable advantage in that direction and therefore is considered a foothill station under REC's proposal. 

Let's now say that on the co-channel of this proposed foothill location, there is a Class-A station at 69 meters HAAT bearing 135 degrees from the LP-250 station.  Let's also assume for this demonstration that the HAAT from the Class-A in the direction of the LPFM is 100 meters.  The minimum distance under §73.807(a) is 67 km.  So under §73.807(a), this distance would be legal.  Along that 135 degree radial, we have determined that the HAAT from the LP-250 station is 101.1 km HAAT.  This means that the 40 dBu F(50, 10) interfering contour of the LPFM station extends out to 44.5km.  The service contour of the Class-A station is the standard 28.3km.  This means that in order for the LPFM's interference contour to not overlap with the Class-A's service contour to not overlap, the two stations must be separated 72.8 km.  In this case, along the 135 degree radial, the LPFM creates interference to the Class-A station up to 3.8 km inside their service contour.  This spacing would not be permitted under translator rules in most cases.

NOTE: The Razorcake proceeding that we are about to bring up is still open and subject to FCC decision.  Please do not bring up this specific case in any comments you file with the FCC.  To do so may be considered a violation of the FCC's ex parte presentation rules.

The foothill station rule stems from an Informal Objection that was make against Razorcake/Gorsky Press, the applicant for an LPFM station on 92.7 in Pasadena, CA.  In their argument, Educational Media Foundation, licensee of KYLA, Fountain Valley, CA states that because of Razorcake's foothill location in Pasadena, the LP-100 signal will create an interference contour that extends into the service contour of KYLA.  

In another case in Northern California, the full-power station was the foothill station.  In a Petition to Deny filed against Women's Civic Improvement Club of Sacramento, Lotus Broadcasting makes a claim that because of the height and power of full power station KMJE, that the LPFM will create interference into their service contour.  In this case, there was a settlement agreement where the LPFM applicant moved to a different channel. 

The latter case is more likely to take place in areas like California where there are grandfathered "super power" FM stations. 

In the past, NAB and others have stated that LPFM stations in these situations could create interference to existing full-power service contours.  Much of the cases of actual contour overlap are suppressed by the 20 km buffer zone that is added on to the minimum spacing requirement of each full-power FM station on co-channel and first-adjacent channel.  Even if LPFM had "translator rules" for spacing,  this spacing would not be allowed. 

The FCC has a rule §73.209(c) which states that full-power stations are not protected from existing or modified LPFM stations that meet §73.807(a) spacing.  While this rule may work well for LP-100, we do not feel that it would work as well for LP-250.  Therefore, in order to address the issue of potential contour overlap due to the use of a distance spacing model, we are proposing that any LP-250 station that will have a proposed 60 dBu service contour of more than 12.7 km in any of 360 different directions as well as any full-power station that has a service contour that extends to the class reference power and HAAT plus 10 dB would be subject to an additional study by the LPFM station to demonstrate that in addition to meeting the minimum distances in §73.807(a) (which are statutorily required by the LCRA), they must also pass a contour overlap study.  

REC proposes no changes to existing LP-100 stations. 

While full-power commercial FM stations also use distance spacing, in their world, the interference protection works both ways.  If we used full-power style distance spacing in LPFM, this means that the San Fernando Valley example above, the Class-A would need to be spaced at least 94 km from the LPFM in order for the LPFM to use that channel thus reducing our channel availability.   Due to its secondary status, LPFM is a "guest" on the dial and REC is willing to make reasonable accomodations in order to permit LP-250 stations on the air in a method that will avoid interference to full-power stations. The foothill station approach for a small subset of low-power and full-power stations is the most reasonable approach to address these extenuating circumstances without holding back the ability for many more LPFM stations across the country to be able to grow. 

 

Last update:
2015-05-18 16:39
Author:
Michelle Bradley
Revision:
1.1
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