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Navigation & Communication
Satellite Communication (VSAT)
A maritime VSAT system holds a stabilised dish on a geostationary satellite while the unit rolls and yaws, and gives broadband to shore for operations data, video and crew welfare. The sub-Category covers C-band, Ku-band and Ka-band antennas, radomes, antenna control units, block upconverters, LNBs and dual-antenna switching, as complete systems or spares.
How a stabilised VSAT terminal works
The antenna pedestal carries motors and inertial sensors that hold the dish on the satellite in roll, pitch and yaw. The antenna control unit (ACU) points it from ship's heading and position, then tracks the signal peak. The block upconverter (BUC) amplifies the transmit signal. The low-noise block downconverter (LNB) receives. A satellite modem, usually supplied by the service provider, links the terminal to your network.
The derrick, cranes and flare boom block the view on some headings. Many drilling units fit two antennas with an arbitrator that switches to whichever one has a clear line to the satellite.
Bands and configurations
- C-band (around 4 and 6 GHz) fades least in heavy rain and gives wide beams, but needs a large dish.
- Ku-band (around 11 to 12 and 14 GHz) uses smaller dishes and has wide regional coverage.
- Ka-band (around 20 and 30 GHz) gives high throughput on spot-beam networks, with more rain fade.
Some antennas convert between Ku and Ka by changing the feed and RF parts. Low earth orbit services with flat-panel terminals now run on many units, often with VSAT kept for coverage, contracted capacity or backup.
Key specifications
| Parameter | Why it matters | Typical classes or units |
|---|---|---|
| Band | Network and rain performance | C, Ku or Ka |
| Dish diameter | Gain and off-axis limits | m and ft |
| BUC power | Uplink margin | W |
| Stabilisation | Motion on your hull | Axes, degrees of roll and pitch |
| Network approval | Whether the operator lets it transmit | Per satellite operator or network |
Standards and approvals for a used antenna
Satellite operators allow only approved or characterised terminals on their networks, because off-axis emissions interfere with neighbouring satellites. A Ka-band terminal is usually tied to the network it was approved for. The ITU allows earth stations on board vessels (ESV) in C and Ku bands under Resolution 902, with limits on off-axis power and distance from the coast. Below-deck units follow IEC 60945 or the class environmental tests. Check the RF radiation hazard distance around the antenna and the unit's hazardous-area drawing, since a radome inside a classified zone needs Ex certification.
Failure modes and inspection
- Radomes crack and let water into the pedestal.
- Drive belts, motors and encoders wear, and inertial sensors drift.
- BUCs fail from heat, and LNBs from water ingress.
- Coaxial or fibre IF links between the radome and below deck degrade.
A survey checks the radome and dish for damage, runs the ACU self-test and pointing test, reads the error log, and measures transmit power and cross-polarisation isolation during commissioning with the satellite operator.
Documentation
- Network approvals for the antenna and its RF parts.
- Serial numbers and age of BUC, LNB and ACU.
- ACU firmware and configuration backup, including blockage zones.
- Last commissioning report.
Integration with your unit
The ACU needs ship's heading from a gyrocompass, often by IEC 61162, and position from GNSS. Plan the antenna position for clear sky, structural support and radiation hazard distance. Budget for a modem and service contract from your provider. The terminal feeds the unit's network through a firewall and switches.
Refurbishment, used or surplus
OEMs and service partners replace belts, motors, sensors and RF parts. A used antenna is a solid spare where you already run the same model and band. Large C-band antennas cost a lot new, so surplus units are worth a look. Where LEO terminals have replaced VSAT on a unit, the retired antennas are often well kept.
Related equipment
The VSAT link enters the unit through data communication equipment. Distress traffic still needs GMDSS radios. Naventr can ask the Seller which networks and satellites the antenna last worked on.
FAQ
Frequently asked questions
Can a used VSAT antenna move to a different satellite provider?
Sometimes, depending on band and approvals. C-band and Ku-band antennas often work across several providers once the new satellite operator accepts them. Ka-band antennas are usually tied to one network. The new provider supplies its own modem and service.
What is the difference between C-band, Ku-band and Ka-band VSAT?
C-band suffers least from rain fade and needs the largest dish, Ku-band uses smaller dishes with wide coverage, and Ka-band gives the highest throughput on spot-beam networks but fades more in heavy rain. Your region and provider decide which fits.
Why do drilling units fit two VSAT antennas?
Two antennas keep the link up when the derrick, cranes or flare boom block one antenna's view of the satellite. An arbitrator switches traffic to the antenna with a clear line of sight as the unit's heading changes.
What should I check on a used VSAT radome and pedestal?
Check the radome for cracks and water inside, the dish for dents, and the belts, motors, encoders and sensors for wear. Ask for the BUC and LNB models and age, the network approvals, the ACU firmware and a recent self-test log.
Does a VSAT antenna need a gyrocompass input?
Yes, most maritime VSAT controllers need ship's heading to acquire the satellite and hold pointing through turns. Check the heading input the ACU expects, usually an IEC 61162 sentence, and that your gyro distribution has a spare output.
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