47 CFR 90.315 - Special provisions governing use of frequencies in the 476-494 MHz band (TV Channels 15, 16, 17) in the Southern Louisiana-Texas Offshore Zone.
(a) The frequency bands from 490-491 and 493-494 MHz will be available for assignment to stations governed by this part within Zone A. The boundaries of Zone A are from longitude 87°45′ on the east to longitude 94°00′ on the west, and from the 3-mile limit along the Gulf of Mexico shoreline on the north to the limit of the Outer Continental Shelf on the south. The frequency bands from 484-485 and 476-488 MHz will be available for assignment to stations governed by this part within Zone B. The boundaries of Zone B are from longitude 87°45′ on the east to longitude 95°00′ on the west and from the 3-mile limit along the Gulf of Mexico shoreline on the north to the limit of the Outer Continental Shelf on the south. The frequency bands from 478-479 and 481-481 MHz will be available for assignment to stations governed by this part within Zone C. The boundaries of Zone C are from longitude 94°00′ on the east, the 3-mile limit on the north and west, a 281 km (175 mile) radius from the reference point at Linares, N.L., Mexico on the southwest, latitude 26°00′ on the south, and the limits of the Outer Continental Shelf on the southeast. These frequencies may also be assigned to fixed stations located on shore designed to provide communications service within the zone.
(b) Offshore base/mobile, and offshore and shore fixed stations may be authorized.
(c) F2, F3, F4, F9, and A2, A3, A4, and A9 emissions may be authorized.
(d) Offshore stations shall afford cochannel protection to TV stations on Channels 15, 16 and 17. Station operating parameters shall be in accordance with the values given in table 1 of this section.
Table 1 - Protection of Cochannel Television Stations by Offshore Stations Operating in the Southern Louisiana-Texas Offshore Zone (65 dB Protection); Maximum Effective Radiated Power
|Distance from transmitter to co-channel TV station kilometers (miles)||Antenna Height above sea level meters (feet)|
|30.5 (100)||45 (150)||61 (200)|
To determine the maximum permissible effective radiated power:
(1) As specified in § 73.611 determine the distance between the proposed station and the cochannel television station. If the exact distance does not appear in table 1 of this section, the next lower distance separation is to be used.
(2) Opposite this distance figure ERPs are given that may be used for antenna heights of 30.5, 45 or 61 meters (100, 150 or 200 ft) ASL. If the exact antenna height is not shown, the ERP allowed will be that shown for the next higher antenna height.
(e) Shore stations communicating point-to-point with offshore stations will be permitted at least the same ERP as the offshore station, but only in the direction of the offshore station. A directional antenna shall be used and the rearward radiated power from the antenna in a sector ±22 1/2° from the line joining the shore antenna to the cochannel television station shall not exceed those shown in table 2 of this section.
Table 2 - Maximum Rearward Effective Radiated Power Allowed for Shore Stations; Rearward Effective Radiated Power (in Watts) From Shore Antenna in a Sector <±>22 1/2° From the Line Joining the Shore Antenna to the Cochannel Television Station
|Distance from transmitter to cochannel television station: kilometers (miles)||Antenna height above ground in meters (feet)|
|30.5 (100)||45 (150)||61 (200)||91.5 (300)||152.5 (500)||228 (750)|
As an example of the use of tables 1 and 2, assume an offshore station located 290 km (180 mi) from TV Channel 17 located in Bude, Miss. with an antenna height of 30.5 m (100 ft). Table 1 allows this station to operate with 250 W ERP. Now assume the shore station communicating with the offshore station is 48 km (30 mi) from the offshore station and 241 km (150 mi) from Bude, Miss. The shore station antenna height is 152.5 m (500 ft) above ground. The shore station will be allowed the same ERP as the offshore station (250 W) in the direction of the offshore station. Table 2 indicates that the effective radiated power in a sector <±>22 1/2° from the line joining the shore antenna to Bude, Miss. can only be 15 W. Consequently, a directional antenna must be used whose minimum front-to-back ratio over this 45° sector must be at least 12.2 dB. (250 W forward power to 15 W rearward power is a power ratio of 16.6 or 12.2 dB).
(f) To provide cochannel protection to television stations, no shore station will be allowed closer than 193 km miles) from the cochannel television station.
(g) To provide adjacent channel protection to television stations, no shore or offshore station shall be allowed within 128 kilometers (80 miles) of the adjacent channel television station.
(h) Mobile stations shall not operate closer to shore than 6.4 km (4 miles) beyond the three mile limit and shall not operate with an ERP in excess of 100 watts with 9.1 m (30 ft) maximum antenna height.
(i) Mobile stations installed in aircraft shall operate 11 km (7 miles) beyond the three mile limit and shall not operate with an ERP in excess of 1 watt or at heights in excess of 305 m (1000 feet) AMSL.
(1) The following frequency bands are available for assignment in all services for use in the Zones defined in paragraph (a) of this section.
Paired Frequencies (MHz)
(2) Only the first and last assignable frequencies are shown. Frequencies shall be assigned in pairs with 3 MHz spacing between transmit and receive frequencies. Assignable frequency pairs will occur in increments of 6.25 kHz. The following frequencies will be assigned for a maximum authorized bandwidth of 6 kHz: 478.01875, 478.98125, 484.01875, 484.98125, 490.01875, 490.98125, 481.01875, 481.98125, 487.01875, 487.98125, 493.01875, and 493.98125 MHz.
(k) Fixed stations operating point-to-point shall be assigned frequencies beginning with 490.025/493.025 MHz (Zone A), 484.025/487.025 MHz (Zone B) and 478.025-481.025 MHz (Zone C) and progressing upwards utilizing available frequencies toward the end of the band. Offshore base/ mobile stations shall be assigned frequencies beginning at 490.975/493.975 MHz (Zone A), 484.975/478.975 MHz (Zone B) and 478.975/481.975 MHz (Zone C) and progressing downwards utilizing available frequencies toward the beginning of the band. All frequency assignments are subject to the conditions specified in § 90.173.