Daily Image
04-05-2009
Control signaling of the LOFAR High Band Antenna tile
| Submitter: | Eric Kooistra |
| Description: | The pictures show the signaling that controls the beam of the LOFAR High Band Antenna (HBA) tile. The control signaling happens via the coax cable that also carries the radio frequency signal that is received by the HBA. The picture on the left shows first a broadcast message that sets the delays for all 16 tile elements in the HBA. After that the picture shows 16 separate accesses to each tile element to read back the delay values. Note that each read access consists of a request message send to the tile element and a response message received from the tile element. The response message can be recognized by the fact that the voltage low level is raised somewhat. The picture on the right shows a detail of the signaling. The data information is encoded using Manchester encoding. Manchester encoding implies that a '0' bit is signaled as a 'low to high' signal and a '1' bit is signaled as a 'high to low' signal. The receiver decodes the bits from the signal by measuring the time between falling edges. From the picture one can derive that the bit rate is about 5.6 kbps. The control for one HBA tile is implemented using 1 microcontroller at the receiver unit and 16 microcontrollers in the tile. Hence per LOFAR station with 48 HBA tiles there are 816 microcontrollers involved to point the station HBA beam. During last Easter weekend we ran a long test communicating 250000 message sequences like in the left picture to a HBA tile and all went OK. Many people are involved in the HBA development. For the control part of the HBA most work was done by Albert van Duin, Paul Riemers and Eric Kooistra. |
| Copyright: | LOFAR |
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