Pushing the Range of Your SeaSonde
Hardware configuration options to expand the observable range of your SeaSonde,
potentially beyond 300 km
Operating Frequency
One easy way to achieve greater range is to operate at a lower frequency band. This has been known for decades, and is the reason CODAR engineers designed the SeaSonde for operation across a wide band, ranging from 4.4 MHz up to 50
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MHz. The lowest of the SeaSonde transmit frequency bands (within 4.4 - 6 MHz) allows for greater ranges than the higher bands without any increase in radiated power. In general, the average daytime observable range achieved by a SeaSonde operating near 4-6 MHz (Long-Range mode) is typically 160-220 km. Actual coverage varies on many factors, such as exact antenna placement, sea conditions, external noise as well as some user selectable software settings.
Twin Transmit Antennas
Another method for increasing observable range is adding a second transmit (TX) antenna. A single monopole antenna exhibits a uniform, omnidirectional transmit signal pattern, meaning that the radiated power is equally distributed across 360 degrees-- including sections over land. The simple addition of a second transmit antenna allows for (beam control) and through proper orientation & phasing the antennas can direct more power transmitter signal power out towards sea. It is most common for this configuration to be used on the lower SeaSonde bands (5-14 MHz), but is possible at any frequency. This hardware configuration option is available when ordering a new SeaSonde Remote Unit or as a retrofit. The offcial name is Twin Transmit Antenna Configuration.
The directionality of the beam fan produced by the TX antenna pair can be controlled by adjusting the spacing between the two elements. Spacing the two elements closer together will cause the signal strength to "fan out", so that the power is spread across a wider angle. As the two antennas are pulled apart, the resulting beam pattern becomes narrower, sending a stronger signal out towards a more specific angular sector. This produces even greater range, but inside a narrower angle sector. The antenna spacing (and hence the TX beam fan spread) is customized at the radar site and optimized for that SeaSonde user's goals.
SeaSonde Coverage to 334 km Shown
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Dual Transmitter - Twin Transmit
Antenna Configuration for Maximum Range A third way to extend range is to increase the TX radiated power. However, when it comes to increasing power, one quickly reaches the point of diminishing returns on investment. The SeaSonde transmitter output power is 40 watts average, which is low and also highly practical from a design and results perspective. Increasing the output power of a single transmit power supply creates more internal heat, placing more wear on itself and other nearby parts inside the transmitter chassis. Hence these other parts, including heat sinks, must be upgraded to perform under this greater heat stress. This drives the price of a radar up to an uncomfortable cost level.
Instead of increasing power from a single transmitter, CODAR offers a more practical solution –– that is addition of a second transmitter. This SeaSonde Remote Unit configuration is referred to as SeaSonde Dual Transmitter –– Twin Transmit Antenna Configuration. In this setup, two transmitters are connected to a set of twin TX antennas. This doubling of the transmit power and the focusing its beam out towards sea can make a dramatic difference in daytime observable range, extending it by as much as 90 km. To put this into perspective, the range increase is the same as would result from a single transmitter with a single antenna that had its power increased from 40 to nearly 200 watts. A deployment of the special configuration units several years ago in the Gulf of Mexico had radars positioned at bottom of the Southwest Pass in Louisiana and on an oil platform to the west. Daytime average observable ranges for these units consistently stayed above 240 km and at times the Southwest Pass radar unit had ranges up to 340 km were reached.
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| A demonstration of range improvement was conducted in September 2008. Data from a Long-Range SeaSonde unit operating in Bodega, California is shown above. Normal range of this unit is 170-190 km. When the system hardware is modified to Long-Range SeaSonde with the dual transmitter - twin TX antenna configuration the current maps extend out past 300 km in certain sectors. |
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Data Produced by
Long-Range SeaSonde |
Data Produced by
Dual TX- Twin TX Antenna
Long-Range SeaSonde |
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The odd-shaped Vermilion 31A oil platform,
nearly 1000 meters long, had plenty of space
for the Long- Range twin TX antennas
and receive antenna.
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Total vector current map produced by
combining the Vermilion & Southwest Pass radials,
extending to 334 km offshore.
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SeaSonde antennas at Southwest Pass were installed in marshland only accessible by boat. |
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