The Array Hub and Controller

The array communications hub and controller remote operations facility (ROF)
The array ROF includes a satellite transmitter dish for the circuit back to Dallas, a VHF antenna mounted on a telephone pole for the hub to element links, a standby power system, and a building for the electronics.

A single four-element omni-directional antenna at the hub receives data from all array elements, and transmits commands to each elements. At Lajitas, only three VHF frequencies are used for the 9 existing RF linked elements.

Closeup of hub VHF antenna.
In this case a wooden telephone pole was the most economical solution to an antenna tower. In other cases, a commercial steel tower may be used.

The antenna feeds two VHF radio modems connected to an array controller and data concentrator. The output of the concentrator feeds a single satellite circuit going back to Dallas.

Hub Equipment inside the ROF.
From top left to bottom right:

The communications controller polls each element on a command frequency and receives the data back on one of the two data frequencies. Messages are error corrected if needed such that no data is lost due to short transmission errors. The data is then compressed, blocked if needed, and transmitted by satellite modem to the Dallas data center where it is forwarded to other clients.

The high capacity UPS provides up to 4 hours of standby power from a small battery bank. A telephone connection directly to the UPS allows the monitoring state-of-health for the power supply, power cycling the equipment in emergencies, and warning of battery failure.

Since commercial power at Lajitas may frequently be out longer than a few hours, alternative means of powering the satellite transmitter must be available. The radios and communications controller are low enough power to be supplied from batteries if desired.

A 400 watt propane fired thermoelectric generator
The four gas fired units produce 24 volt DC power that was inverted to 110V power to drive a commercial satellite modem. The box on the left end is the power regulator

For over a year, the hub was totally powered from a thermoelectric generator. A large gas tank had to be refilled about every two months, but the system was highly reliable and completely independent of commercial power. Later, during installation of the full array, the system was switched to a more economical UPS operation.

A propane fueled DC generator to back up the UPS battery plant.
The generator is designed for unattended operation, with automated alarms and shutdowns to prevent engine damage in the event of mechanical failure, and reminders for periodic maintanence. This system has been in operation at Lajitas for over a year.

The UPS battery plant motor-generator back up is capable of handling extended power outages. It also supplies sufficient power (3Kw) to run one or more on-site workstations used during experiments. Like the UPS the generator also has the capability for remote state-of-health monitoring.

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