|R.H. van den Brink
| Another 12 LOG subracks are ready for APERTIF. This is the second and last batch to complete 12 APERTIF dishes, nicely assembled on schedule by Sieds Damstra, Eim Mulder and Anne Koster.
The Local Oscillator Generator system (LOG) is a synthesizer generator based on the HITTITE HMC833 PLL. There are two versions at each dish, one for each local oscillator frequency. The two LOG units are required to generate LO1 and LO2 signals for the APERTIF Down Converter Units, called DCU. These systems mix down the antenna signals to the baseband so that the Analog-to-Digital Converter Unit (ADU) can convert it eventually to a digital data stream.
Following the signal through the chain, a reference CLK from the maser enters the input of the buffer card. The differential buffer amplifies and distributes the clock to the PLL-cassette, and to other parts of the APERTIF system who require the clock reference such as other LOG units, ADU (ADC clock) and UNIBOARD. The PLL generates the required LO frequency from the reference CLK. A divider card amplifies and splits these four outputs, where each of them can be amplitude controlled by means of an 15 dB attenuator. All cards can be controlled and monitored by means of the control card. A central control computer (LCU) has access to this control card by means of an Ethernet interface using IP based communication. It uses a TCP stack for this interface. The power card is a low EMI power supply unit, which supplies the cards via the back plane of the LOG system.
As more hardware is getting complete it will be integrated at Westerbork in the coming months.
(*) APERTIF-12 is the second part of the APERTIF project which is divided into two delivery phases. In the first phase (APERTIF-6) six dishes are implemented with the single polarized version of the APERTIF system. In the second phase (APERTIF-12) another six dished will be implemented with the APERTIF system, and all twelve dishes are upgraded to a dual polarized system.
|R.H. van den Brink