Automated Maritime Telecommunications System (AMTS) is a commercial mobile radio service used within the United States. It operates within the

VHF Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF ...

frequency range, just above the North American

Band III Band III is the name of the range of radio frequencies within the very high frequency (VHF) part of the electromagnetic spectrum from 174 to 240 megahertz (MHz). It is primarily used for radio and television broadcasting. It is also called high-b ...

television range, and offers both voice and data communications to maritime customers. The system is operated by a network of private carriers across the country, with coverage primarily including coastal and inland waterways.

History

In 1981, the FCC proposed the Inland Waterways Communication System (IWCS), a commercial maritime radio service with the proposed purpose of expanding private maritime communication and that was to operate from 216 to 220 MHz.R. Eckert: ''Guidance for Evaluating the Potential for Interference to TV From Stations of Inland Waterways Communications Systems'', Federal Communications Commission Office of Science and Technology, 1982 Earlier reports had studied the feasibility of using this frequency band, but warned of the high probability of

adjacent-channel interference Adjacent-channel interference (ACI) is interference caused by extraneous power from a signal in an adjacent channel. ACI may be caused by inadequate filtering (such as incomplete filtering of unwanted modulation products in FM systems), improper t ...

with TV channel 13.L. Middlekamp, H. Davis: ''Interference to TV Channels 11 and 13 from Transmitters Operating at 216-225MHz'', FCC Lab Division Report, Project No. 2229-71, 1975 However, by the early 1980s, it had been estimated that radio tuner technology had advanced to the point that such interference could be minimized. Final approval for auctioning of AMTS spectrum did not come until almost two decades later with the approval of the

Balanced Budget Act of 1997 The Balanced Budget Act of 1997 () was an omnibus legislative package enacted by the United States Congress, using the budget Reconciliation (U.S. Congress), reconciliation process, and designed to balance the federal budget by 2002. This act wa ...

, which required that the FCC auction licenses for such spectrum."Auction of Automated Maritime Telecommunications System Licenses Scheduled For August 3, 2005", FCC DA 05-1047, 2005

Technical specifications

Maximum base station transmit power: 1,000 watts ERPFCC rule §80.215 (h)(1), 2009 Maximum mobile unit transmit power: 18 watts ERPFCC rule §80.215 (h)(5)(i), 2009 The AMTS spectrum may be used in Land Mobile Radio Systems subject to the above-mentioned regulations and TV interference considerations. For example, under the conditions of the service, AMTS spectrum could be used in land-locked (e.g.) Denver to carry mobile radio traffic. Bands bought at auction having Geographic licenses (use inside a defined region, vs. Site Licenses that are only for a point) may be divided into frequency channels per the owner or licensee's discretion. Thus, if the user chooses to use Narrow Band spacings, the number of channels per block is 500 kHz / 12.5 kHz= 40 channels; with Very Narrow Band spacings, the number of channels per block is 500 kHz / 6.25 kHz = 80 channels. Using technology that can support narrower bandwidths in general allows more efficient use of the licensed block. Note that spectra do not have to be purchased in 500 kHz. purchasing (e.g.) 375 kHz is allowed under FCC rules, although the seller may not be amenable to such a proposal.

Restrictions

The AMTS is unique to U.S. waters, having no compatible counterpart in Canada or Mexico. Use is limited to a maximum of 12 nautical miles off the US coast. Interference outside US territorial waters is possible. When used within 105 miles (169 kilometers) of a TV transmitter operating on channel 13 or within 80 miles (129 kilometers) of a TV transmitter operating on channel 10, the FCC requires a plan to limit interference of such TV signals by both base stations and mobile units.FCC rule §80.215 (h)(2), 2009 As such, maximum transmit power may be below 1,000 watts ERP. Lastly, AMTS systems may not interfere with the SPASUR radar system which operates on the adjacent 216.88-217.08 MHz band.

References

{{Reflist Maritime communication