SAMWAS-200 DGPS/NAVTEX Transmitting Antenna System

Technical Services Options Available
Related LBA MW Systems Available

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.

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 engineering 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.
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Related LBA MW Systems Available:

• SAMWAS-100: Efficient short aperture antenna system based on a 100-foot tower for the DGPS and NAVTEX bands.
• SAMWAS-350: Maximum efficiency short aperture antenna system based on a 350-foot tower for the DGPS and NAVTEX bands.
• TUP-3: Family of truck and trailer (C-130 qualified) transportable systems for 250-2500 kHz tactical applications.
• TGR-50: Low power, man-carry emergency system for 250 - 5000 kHz tactical applications.
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