1. Nuts and Bolts of FCC FM Allocations
Doug Vernier – V-Soft Communications
Telecommunication Consultants
Prepared for the SBE Webinar

2. FM Allocations Service Assumptions
Operate within power and antenna height maximum and minimums required for class
Serve the licensed Principal City
Cause no interference
Meet minimum separations
Short space if necessary using rules

3. FM Station Classes Zone I and Zone 1A
East U.S. , Southern California & P.R.
• A (6 kW at 100 m HAAT)
• B1 (25 kW at 100 m HAAT)
• B (50 kW at 100 m HAAT
Zone II – Most of the rest of the U.S.
• A (6 kW at 100 m HAAT)
• C3 (25 kW at 100 m HAAT)
• C2 (50 kW at 150 m HAAT)
• C1 (100 kW at 299 m HAAT)
• C0 (100 kW at 450 m HAAT)
• C (100 kW at 600 m HAAT)

4. Minimum separations
FM band: Channels 200 – – MHz Channel Band Width = 200 kHz

5. Minimum Separations Study

6. Area to Locate Transmitter – 73.207 Plot

7. Service to Principal City
Commercial FM 70 dBu
With 80 percent of the principal city area or population covered.
Non-commercial FM 60 dBu with at least 50% of the principal city covered
The FCC has allowed waivers where the applicant uses TechNote 101 calculations (Longley-Rice)

8. Protected F(50-50) Contour Distances
Class A, 3 kW = 24.2 km, old class A
Class A, 6 kw = km, 60 dBu (1 mV/m)
Class B1 = 44.7km, 57 dBu
Class B = 65.1 km, 54 dBu
Class C3 = 39.1 km, 60 dBu
Class C2 = 52.2 km, 60 dBu
Class C1 = 72.3 km, 60 dBu
Class C0 = 83.4 km, 60 dBu
Class C = 91.8 km, 60 dBu
Class L1 = 5.2 km

9. FCC Coverage CURVES F(50-50)

10. 73.215 and 73.509 Contour Protection Ratios – D to U
Co-channel: dB - *if 60 dBu is protected F(50-10) interference contour = 40 dBu
First-Adjacent: - 6 dB
2nd and 3rd adjacent +40 dB * if the 60 dBu is the protected contour, interference contour = 100 dBu 

11. Interference Curves F(50-10)

12. Where did the D/U ratios come from?
Project # In 1947, the FCC "Laboratory Division" conducted tests on FM Radios and published reports on "Characteristics of Commercial FM Broadcast Receivers".
Data was included in the results concerning the interference rejection ratios on both co-channel and adjacent channels.
These measurements are the basis for the interference ratios still used in the FM rules (first adopted in 1951.)

13. Converting Curves to Machine readable tables

14. F(50-10) FORTRAN TABLE
* F(50,10) FIELD STRENGTH DATA FOR THE LOW VHF PROPAGATION CURVE *
* ( FM AND TV CHANNELS 2 THRU 6 ) *
DATA ( ( F51LV(I,J), J = 1, IH10 ), I = 1, ID10 ) /
& , 58.4, 64.3, 68., 70.5, 72.3, 74.2, 75.9, 77., 78.2,
& , 81.8, 82.2, C
& , 47., 53., 56.5, 59., 60.9, 63., 64.8, 66.2, 67.6,
& , 73.8, 75.5,
& , 40.9, 45.9, 49., 51.7, 53.7, 56., 57.9, 59.6, 60.9,
& , 67., 69.,
& 33., 36., 39.9, 43., 45.4, 47.5, 50., 52., 54., 55.2,
& , 61.4, 63.3,
& 30., 31.9, 35., 37.7, 40., 41.9, 44.4, 46.7, 48.5, 50.,
& , 56.3, 58.4,

15. HAAT FM - radial 3 to 16 km
Minimum of 51 elevation points along a radial

16. Radials for Determining Average HAAT

17. Digital Terrain Elevation Databases

18. Popular Terrain ElEvation Databases
3 arc-second and 30 arc-second U.S.G.S. databases in use today by the FCC have the least accuracy of available databases.
The 30 arc-second database was derived from the original 3 arc-second U.S.G.S. data base which was digitized from 1:250,000 scale maps.
Since each second of latitude approximates 100 feet, the 30 arc-second terrain elevation database will have an elevation point every 3,000 feet. The 3 arc- second database will have a point every 300 feet.
Both databases are said to have a number of errors in them such as mountain
peaks being off as much as 15 seconds.
In 2004 the USGS released the National Elevation Datum (NED) data set.
This dataset was developed by merging the highest-resolution, best quality elevation data available across the United States into a seamless raster format. NED is the result of the maturation of the USGS effort to provide 1:24,000-scale Digital Elevation Model (DEM) data for the conterminous US and 1:63,360-scale DEM data for Alaska.
The newest database to be released is from the Shuttle Radar Topography Mission (SRTM). In this mission NASA obtained elevation data on a near global scale to generate the most complete high-resolution digital topographic database of the Earth.

19. ReturnING to Minimum Separations Study
Where they came from

20. Spacings Table
It’s based on “flat earth” and uniform terrain.

21. FM Short-Spacing Under 73.215
separations cannot be met
Short-space distance must be less than what is shown in (e)
If the protected station is not already a short-space facility, you must change its power and HAAT to the standard class maximum
If protected station is directional assume its an omnidirectional facility
Use contour to contour protection to short-spaced station.

22. The underground antenna

23. KWVE-FM with Antenna at Licensed Height and Power – Using Omni antenna

24. KWVE-FM with OMNI Antenna

25. KUZZ-FM Antenna Goes Underground
Real Antenna at 6 kW HAAT: 416M
Antenna at 50 kW HAAT: 150M

26. Grand Fathered Shortspace Assignments 73.213
These assignments are numerous in Zone 1
Created before 1964 and adoption of separations tables
Pre 1989 short-space caused by allowing all class A stations to increase from 3 kW to 6 kW
2nd and 3rd adjacent spacing requirements are not followed allowing a stations transmitter to be within the protected contour of the shortspaced station.