DGPS Testing for USCG - Biorka, Alaska

LBA provides equipment and services to support shore station requirements for modern maritime communications in the low frequency, medium frequency, and high frequency radio bands

At LBA, we manufacture an unsurpassed line of shore transmitting and receiving antennas for all these services. We can supply all ofthe other equipment required for most shorestation applications.

With over 50 years experience in LF, MF, and HF transmission worldwide, we can design, furnish, install, and maintain virtually any type shore system anywhere in the world.

Critical operations in the MF and HF bands are typically associated with the communications requirements of the GMDSS, as well as traditional radiotelephone communications. The MF and LF bands are also used to support DGPS and LORAN navigation systems. Below is a brief view of the various LF, MF, and HF modalities currently in use, and their technical outlines. We also provide convenient links to LBA products and services, and other resources useful to the maritime systems planner or manager.
 

An Overview of the Global Maritime Distress & Safety System 

Since the invention of radio at the end of the 19th Century, ships at sea have relied on Morse code, invented by Samuel Morse and first used in 1844, for distress and safety telecommunications.

Over fifteen years ago the International Maritime Organization (IMO), a United Nations agency specializing in safety of shipping and preventing ships from polluting the seas, began looking at ways of improving maritime distress and safety communications.

This resulted indevelopment by IMO of a Global Maritime Distress and Safety System (GMDSS) to provide the communication support needed to implement the search and rescue plan. This new system is based upon a combination of satellite and terrestrial radio services, and has changed international distress communications from being primarily ship-to-ship based to ship-to-shore (Rescue Coordination Center) based. It spelled the end of Morse code communications and provides for automatic distress alerting and locating.
 

Communications Requirements for GMDSS Sea Areas

GMDSS sea areas serve two purposes: to describe areas where GMDSS services are available, and to define what GMDSS ships must carry.

Prior to the GMDSS, the number and type of radio safety equipment ships had to carry depended upon its tonnage. With GMDSS, the number and type of radio safety equipment ships have to carry depend upon the areas in which they travel.
 

GMDSS Sea Areas Are of Four Types

Sea Area A1 An area within the radiotelephone coverage of at least one VHF coast station in which continuous DSC (ch70) alerting and radiotelephony services are available. VHF shore stations typically serve ships in an area out to 25 miles at sea.

Sea Area A2 An area, excluding Sea Area Al, within the radiotelephone coverage of at least one MF coast station in which continuous DSC (2187.5 kHz) alerting and radiotelephony services are available. MF coast stations may serve ships out to about 200 miles at sea using groundwave communications.

Sea Area A3 An area, excluding sea areas Al and A2, within the coverage of an INMARSAT geostationary satellite in which continuous alerting is available. Ships in this area may also be served by shortwave (HF) DSC coast stations.

Sea Area A4 The area outside that covered by areas A1, A2 and A3 is called Sea Area A4. No specified service is available, but ships traveling these polar regions must carry a DSC-equipped HF radiotelephone/telex, in addition to equipment required for areas A1 and A2.

 
The GMDSS consists of many separate systems the use of which depends upon the ship's sea area of operation. An array of radio navigation systems is also available to the mariner. Some of the principle systems which utilize the LF, MF, and HF bands are discussed further here.
 

Digital Selective Calling (DSC) Systems

MF/HF radiotelephone service is offered to mariners as part of the GMDSS.

This service, called digital selective calling (DSC),allows mariners to instantly send an automatically formatted distress alert to the local Coast Guard or other rescue authority anywhere in the world. Digital selective calling also allows mariners to initiate or receive distress, urgency, safety and routine radiotelephone calls to or from any similarly equipped vessel or shore station, without requiring either party to be near a radio loudspeaker.

DSC acts like the dial and bell of a telephone, allowing you to "direct dial" and "ring" other radios, or allow others to "ring" you, without having to listen to a speaker. New VHF and HF radiotelephones have DSC capability.
 

NAVTEX Alerting System 

NAVTEX is an international, automated system for instantly distributing maritime navigational warnings, weather forecasts and warnings, search and rescue notices and similar information to ships.
Example of typical NAVTEX transmission:

A small, low-cost and self-contained "smart" printing radio receiver installed in the pilot house of a ship or boat checks each incoming message to see if it has been received during an earlier transmission, or if it is of a category of no interest to the ship's master.
A new ship coming into the area will receive many previously-broadcast messages for the first time; ships already in the area which had already received the message won't receive it again. No person needs to be present during a broadcast to receive vital information. 

  
Differential GPS (DGPS) Service
The DGPS Service broadcasts correction signals on marine radiobeacon frequencies to improve the accuracy and integrityto GPS-derived positions. The US Coast Guard DGPS Service, for example, provides 10-meter accuracy in all established coverage areas. Many nations are implementing standard DGPS services modeled after the U.S. Coast Guard's system to significantly enhance maritime safety in their critical waterways.

The US maritime DGPS service provides integrity alarms for GPS and DGPS out-of-tolerance conditions within 10 seconds of detection, availability of 99.7% per month, coastal coverage to the continental United States, the Great Lakes, Puerto Rico/US Virgin Islands, and selected portions of Alaska and Hawaii.

Typically, the positional error of a DGPS position is 1 to 3 meters,greatly enhancing harbor entrance and approach navigation.
In addition, the US Coast Guard has extended the DGPS system to redundantly cover most of the continental United States in its Nationwide DGPS (NDGPS) program.

Differential GPS (DGPS) Service Areas
Australian Government DGPS
Canadian DGPS
Canadian DGPS General Information
The Commissioners of Irish Lights (Irish DGPS Service)
European DGPS Beacons
IALA DGNSS International Association of Marine Aids to Navigation and Lighthouse Authorities
Northern Lighthouse Board DGPS Scotland
Trinity House - General Lighthouse Authority for England, Wales, the Channel Islands and Gibraltar
U.S. Coast Guard DGPS (U.S. National DGPS)
German DGPS Stations
 

LORAN-C Navigation Service 

LORAN-C was originally developed to provide radio navigation service for U.S. coastal waters and was later expanded to include complete coverage of the continental U.S. as well as most of Alaska.

Twenty-four U.S. LORAN-C stations work in partnership with Canadian and Russian stations to provide coverage in Canadian waters and in the Bering Sea. LORAN chains also operate in Europe and other parts of the world.

LORAN-C provides better than 0.25 nautical mile absolute accuracy for suitably equipped users within the published areas.
LORAN-C is approved as an en route supplemental air navigation system for both Instrument Flight Rule (IFR) and Visual Flight Rule (VFR) operations. It serves to also provide a host of other navigation, location, and timing services for both civil and military air, land and marine users.
NOTE: The US and Canadian LORAN chains were shut down in 2010. Some operations continue in other parts of the worlds.  


 
GMDSS & DGPS Antenna Systems

SAMWAS-100: Efficient short aperture antenna system based on a 100-foot tower for the DGPS and NAVTEX bands.
SAMWAS-200: NAVTEX MW short aperture antenna system based on a 200-foot tower for the DGPS and NAVTEX bands.
SAMWAS-350: DGPS MW short aperture antenna system based on a 350-foot tower for the 300 kHz DGPS band.
TGR-50: Antenna System for 2MHz GMDSS Transmit or Recieve Service.

  
SAMWAS-100 DGPS/NAVTEX Transmitting Antenna System
The LBA Technology SAMWAS-100 is a heavy duty, compact, very short aperture medium wave transmitter antenna system. The SAMWAS-100 is designed to fit completely on a site as small as 100 feet (30 meters) in radius. Designed to operate on a single frequency from 275 kHz to 530 kHz, it uses a unique electrically short radiator and peripherals to provide reliable and cost effective omnidirectional coverage for DGPS and radio navigation applications. The SAMWAS-100 replaces all previous conventional-type DGPS and NAVTEX antenna systems.

Unsurpassed Range Vs. Height Coverage Performance
The SAMWAS-100 can provide 300 kHz DGPS correction signals for safety and warning information to mariners over approximately 70% of the groundwave and skywave coverage achievable from a full ¼ wave vertical antenna, using a structure under 15% of that height.  Even better coverage performance is realized on the 490 and 518 kHz NAVTEX frequencies.

Advanced Radiator Design
The low-Q design of the SAMWAS-100 DGPS/NAVTEX antenna system minimizes voltages compared to high-Q conventional designs. Because of its low-Q trapezoidal feed design, more transmitter power gets through the antenna radiator, safely, than in conventional systems. System stability is unmatched by conventional whips and narrow towers. The low-Q design, coupled with a proprietary top loading and ground reference system, isolates the antenna system impedance from changing earth conditions, while providing a low loss ground termination path.

Overall system height is 108 feet (33 meters) above ground.  The high efficiency system utilizes an insulated vertical radiator antenna tower with proprietary enhanced top loading and a trapezoidal symmetrical unipole Q-reduction system. The radiator is rated for 1000 watts, MSK modulated, continuous duty, which is conservative for reliable service at the typical lower power levels in the 300 kHz DGPS band. Higher power levels can be accommodated on request.  Proprietary Delta Unit™ auto tensioning terminations ensure radiator system stability.
Although lighting is not normally required at this height, a toroidal ring air gap transformer can provide aviation hazard lighting isolation if required. Standard subsystem components are to EIA/TIA-222-F. Typical tower structure components are hot-dip galvanized.  Safety features include safety climb devices.

The antenna tuning system provides an interface between the DGPS/NAVTEX transmitting Tower Radiator Subsystem and a 50-ohm coaxial transmission line. The ATU-1 is rated for 1000 watts, MSK or PSK modulated, continuous duty in the 300 kHz band (the ATU-2.5 is available to 2500 watts transmitting power in the 500 kHz band).  Antenna tuning systems for higher or lower transmitting power can be provided with similar performance to the ATU-1.  The inherent stability of the low-Q antenna makes constant retuning unnecessary. The system is highly reliable, as there are no active components or control circuits in the ATU-1.  

While a ¼ wave buried copper wire ground plane is recommended, above ground and shorter buried ground systems may be accommodated.  To enhance stability of the short radiator under varying weather and earth conditions, and to improve displacement current collection at the base of the tower, a proprietary cantilevered six element radial capacitance reference is provided for above ground installation on the Radiator Subsystem base structure.

Minimum Life Cycle Support Costs
The SAMWAS system components are designed for the high reliability and minimum life cycle support costs demanded by critical DGPS, NAVTEX and radio navigation missions. Using standard parts and maximum commonality in subsystems ensures lowest cost life cycle maintenance. 

High Reliability
Reliability is further enhanced by the use of galvanically compatible structural materials, computer confirmed mechanical and electrical safety factors, and special attention to insulator endurance under salt spray and high solar conditions.  The system is designed and installed to endure local ice and wind conditions.  The SAMWAS antenna system radiating structure uses high-flashover, corona protected guy insulators as needed to protect against lightning and other voltage-induced outages.

Since installation and performance can be influenced by geotechnical siting conditions, coupled RF energy from nearby antennas, and other local effects, an LBA site survey before design completion is recommended.
 
  
SAMWAS-200 DGPS/NAVTEX Transmitting Antenna System 
Download Current SAMWAS-200 Specsheet (PDF)

The LBA Technology SAMWAS-200 is a heavy duty, compact, very short aperture medium wave transmitter antenna system. The SAMWAS-200 is designed to fit completely on a site as small as 200 feet (60 meters) in radius. Designed to operate on a single frequency from 275 kHz to 530 kHz, it uses a unique electrically short radiator and peripherals to provide reliable and cost effective omnidirectional coverage for DGPS and radio navigation applications. The SAMWAS-200 replaces all previous conventional-type DGPS and NAVTEX antenna systems.
The SAMWAS-200 is capable of transmitting any two frequencies separated by 15% or more in the 285 - 530 kHz medium wave band, when equipped with an LBA diplexing system.

Unsurpassed Range Vs. Height Coverage Performance
The SAMWAS-200 can provide 300 kHz DGPS correction signals for safety and warning information to mariners over approximately 80% of the groundwave and skywave coverage achievable from a full ¼ wave vertical antenna, using a structure under 25% of that height.  Even better coverage performance is realized on the 490 and 518 kHz NAVTEX GMDSS frequencies.

Advanced Radiator Design
The low-Q design of the SAMWAS-200 DGPS/NAVTEX antenna system minimizes voltages compared to high-Q conventional designs. Because of its low-Q trapezoidal feed design, more transmitter power gets through the antenna radiator, safely, than in conventional systems. System stability is unmatched by conventional whips and narrow towers. The low-Q design, coupled with a proprietary top loading and ground reference system, isolates the antenna system impedance from changing earth conditions, while providing a low loss ground termination path.

Overall system height is 199 feet (60.6 meters) above ground.  The high efficiency system utilizes an insulated vertical radiator antenna tower with proprietary enhanced top loading and a trapezoidal symmetrical unipole Q-reduction system. The radiator is rated for 2500 watts (5000 watts at 500 kHz), MSK modulated, continuous duty, which is conservative for reliable service in DGPS and NAVTEX applications. Higher power levels may be accommodated on request.  

Although lighting is not normally required at this height, medium intensity strobe lights and a toroidal ring air gap transformer can provide aviation hazard lighting if required.

Standard subsystem components are to EIA/TIA-222-F. Typical tower structure components are hot-dip galvanized.

Safety features include safety climb devices.  The antenna tuning system provides an interface between the DGPS/NAVTEX transmitting Tower Radiator Subsystem and a 50-ohm coaxial transmission line. Selection of ATU is a function of the operating power. The ATU-2.5 is rated for 2500 watts, MSK or PSK modulated, continuous duty in the 300 kHz band (the ATU-5SF is available to 5000 watts transmitting power in the 500 kHz band).  Antenna tuning systems for higher or lower transmitting power can be provided with similar performance to the ATU-2.5.  The inherent stability of the low-Q antenna makes constant retuning unnecessary.  The system is highly reliable, as there are no active components or control circuits in the LBA ATU systems.  

Optional ATU-(*)SFA frequency agile tuning unit for 518/490 kHz: The SAMWAS-200 system can be supplied for dual frequency operation using the ATU-(*)SFA.  This unit is designed to take two inputs and sequentially switch them in accord with non-conflicting time slots to provide a two frequency NAVTEX broadcast capability.

While a ¼ wave buried copper wire ground plane is recommended, above ground and shorter buried ground systems may be accommodated.  To enhance stability of the short radiator under varying weather and earth conditions, and to improve displacement current collection at the base of the tower, a proprietary cantilevered six element radial capacitance reference is provided for above ground installation on the Radiator Subsystem base structure.

Minimum Life Cycle Support Costs
The SAMWAS system components are designed for the high reliability and minimum life cycle support costs demanded by critical DGPS, NAVTEX and radio navigation missions. Using standard parts and maximum commonality in subsystems ensures lowest cost life cycle maintenance.

High Reliability
Reliability is further enhanced by the use of galvanically compatible structural materials, computer confirmed mechanical and electrical safety factors, and special attention to insulator endurance under salt spray and high solar conditions.  The system is designed and installed to endure local ice and wind conditions. The SAMWAS antenna system radiating structure uses high-flashover, corona protected guy wire insulators as needed to protect against lightning and other voltage-induced outages.

Since installation and performance can be influenced by geotechnical siting conditions, coupled RF energy from nearby antennas, and other local effects, an LBA site survey before design completion is recommended.
 
  
SAMWAS-350 DGPS/NAVTEX Transmitting Antenna System 
 
The LBA Technology SAMWAS-350 is a heavy duty, compact, very short aperture medium wave transmitter antenna system. The SAMWAS-350 is designed to fit completely on a site as small as 200 feet (60 meters) in radius.  Designed to operate on a single frequency from 275 kHz to 530 kHz, it uses a unique electrically short radiator and peripherals to provide reliable and cost effective omnidirectional coverage for DGPS and radio navigation applications. The SAMWAS-350 replaces all previous conventional-type DGPS and NAVTEX antenna systems.

The SAMWAS-350 is capable of transmitting any two frequencies separated by 15% or more in the 285 – 530 kHz medium wave band, when equipped with an LBA diplexing system.

The SAMWAS NAVTEX antenna radiating structure uses no base insulator and is directly grounded.  The grounded tower provides inherent system lightning protection, and permits easy mounting of other antennas for communications, such as for the USCG Rescue 21 program, or for microwave links, without impact on medium wave transmission.
 
Unsurpassed Range Vs. Height Coverage Performance
The SAMWAS-350 can provide 300 kHz DGPS correction signals for safety and warning information to mariners over approximately 87% of the groundwave and skywave coverage achievable from a full ¼ wave vertical antenna, using a structure under 40% of that height.  Even better coverage performance is realized on the 490 and 518 kHz NAVTEX GMDSS frequencies.

Advanced Radiator Design
The low-Q design of the SAMWAS-350 DGPS/NAVTEX antenna system minimizes voltages compared to high-Q conventional designs. Because of its low-Q trapezoidal feed design, more transmitter power gets through the antenna radiator, safely, than in conventional systems. System stability is unmatched by conventional whips and narrow towers. The low-Q design, coupled with a proprietary top loading and ground reference system, isolates the antenna system impedance from changing earth conditions, while providing a low loss ground termination path.

Overall system height is 350 feet (60.6 meters) above ground.  The high efficiency system utilizes an insulated vertical radiator antenna tower with proprietary enhanced top loading and a trapezoidal symmetrical unipole Q-reduction system. The radiator is rated for 5000 watts, MSK modulated, continuous duty, which is conservative for reliable service in DGPS and NAVTEX applications. Higher power levels may be accommodated on request.

Medium intensity strobe lights and a toroidal ring air gap transformer typically provide aviation hazard lighting.

Standard subsystem components are to EIA/TIA-222-F. Typical tower structure components are hot-dip galvanized.  Safety features include safety climb devices.

The antenna tuning system provides an interface between the DGPS/NAVTEX transmitting Tower Radiator Subsystem and a 50-ohm coaxial transmission line. Selection of ATU is a function of the operating power. The ATU-5 is rated for 5000 watts, MSK or PSK modulated, continuous duty within in the 300 and 500 kHz bands. Antenna tuning systems for higher or lower transmitting power can be provided with similar performance to the ATU-5.  The inherent stability of the low-Q antenna makes constant retuning unnecessary.  The system is highly reliable, as there are no active components or control circuits in the LBA ATU systems.  

Optional ATU-(*)SFA frequency agile tuning unit for 518/490 kHz: The SAMWAS-350 system can be supplied for dual frequency operation using the ATU-(*)SFA.This unit is designed to take two inputs and sequentially switch them in accord with non-conflicting time slots to provide a two frequency NAVTEX broadcast capability.

While a ¼ wave buried copper wire ground plane is recommended, above ground and shorter buried ground system may be accommodated.  To enhance stability of the short radiator under varying weather and earth conditions, and to improve displacement current collection at the base of the tower, a proprietary cantilevered six element radial capacitance reference is provided for above ground installation on the Radiator Subsystem base structure.

 

Minimum Life Cycle Support Costs
The SAMWAS system components are designed for the high reliability and minimum life cycle support costs demanded by critical DGPS, NAVTEX and radio navigation missions. Using standard parts and maximum commonality in subsystems ensures lowest cost life cycle maintenance.

High Reliability

Reliability is further enhanced by the use of galvanically compatible structural materials, computer confirmed mechanical and electrical safety factors, and special attention to insulator endurance under salt spray and high solar conditions. The SAMWAS antenna system radiating structure uses high-flashover, corona protected guy wire insulators as needed to protect against lightning and other voltage-induced outages.

Since installation and performance can be influenced by geotechnical siting conditions, coupled RF energy from nearby antennas, and other local effects, an LBA site survey before design completion is recommended.

Technical Services Options Available:
Turnkey construction and commissioning: Site survey, design, permitting, site preparation, construction, and commissioning services on an E, F & I basis using qualified resources. Includes “as-built” documentation.

A la Carte technical services: Qualified personnel can be provided for such services as site qualification, installation commissioning, and performance verification.

Inspection, rehabilitation and upgrade of existing transmitter systems.

Emergency and maintenance service: Available on an off-air response or routine basis for all system components, including scheduled inspections and periodic performance revalidation.