| 26,8 → 26,18 |
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| We have the capacities necessary to develop a receiver which will have a wide bandwidth, a high third-order intercept point and preferably an option for phase and frequency locking to other receivers located at other radioastronomical sites on the Earth. Currently there exist several receivers with the above-mentioned parameters, for example USRP2, USRP B210 \cite[USRP-sdr] \glos{USRP}{Universal Software Radio Peripheral} or HackRF \cite[hackrf-sdr] which are commercially available. However all of them lack scalability and have higher prices unaffordable to our amateur radioastronomical network. Scalability and redundancy are the main requirements of the noise reduction algorithms and thus acted as a motivation for this diploma thesis. |
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| New radio astronomical systems such as LOFAR\glos{LOFAR}{Low-Frequency Array} are explicit examples of the scalability and redundancy approach. LOFAR has a completely different and novel structure developed to solve the problems of radioastronomy signal reception. It uses exclusively multi-antenna arrays and mathematical algorithms for signal handling. Radio signals recorded by LOFAR can be used in multiple ways: radio images can be computed (if sufficient cover of $u/v$ plane is achieved), the radiation intensity can be measured, the spectrum can be analysed for velocity measurement, etc. |
| New radio astronomical systems such as LOFAR\glos{LOFAR}{Low-Frequency Array}~\cite[lofar] are explicit examples of the scalability and redundancy approach. LOFAR has a completely different and novel structure developed to solve the problems of radioastronomy signal reception. It uses exclusively multi-antenna arrays and mathematical algorithms for signal handling. Radio signals recorded by LOFAR can be used in multiple ways: radio images can be computed (if sufficient cover of $u/v$ plane is achieved), the radiation intensity can be measured, the spectrum can be analysed for velocity measurement, etc. |
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| LOFAR is an innovative radioastronomy system which uses a phased antenna array approach at an enormous scale. Thousands (around $2 \cdot 10^4$) of antennas are manufactured and deployed in the field. The centre of LOFAR system is situated in the Netherlands and peripheral antennas with the connection network extend to other European countries. |
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| \midinsert |
| \clabel[lofar-antenna]{Lofar antenna configuration} |
| \picw=10cm \cinspic ./img/lofar_antenna.jpg |
| \caption/f One LOFAR LBA\glos{LBA}{Low Band Antenna} antenna element. |
| \endinsert |
| |
| Due to the size of the whole system, the LOFAR project has to use a low cost hardware. A special construction techniques were employed to keep the overall project budget at acceptable level (including for example specially designed polystyrene supporting blocks for High Band Antenna (HBA\glos{HBA}{High Band Antenna})). Many of used components are manufactured on a massive scale for other than scientific use. LBA antennas' masts are made from a standard Polyvinyl chloride (PVC\glos{PVC}{Polyvinyl chloride}) plastic waste pipes \ref[lofar-antenna]. The entire project was designed by the Netherlands Institute for Radio Astronomy which produces many similarly sophisticated devices~\cite[astron-devices]. |
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| \sec Required receiver parameters |
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| The novel approach of the receiver construction described above goes hand-in-hand with the new requirements on receiver parameters as well. No additional attempts to improve the signal-to-noise ratio on single antenna have been performed currently. There are however other parameters, that are requested nowadays. |
| 82,17 → 92,8 |
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| Custom designs usually use non-recurring engineering for the development of a specific solution for an observational project. Consequently, such instruments are very costly if they are not reproduced multiple times. A typical example of the instrument developed and manufactured in a single piece with enormous funding requirements was the Arecibo ALFA\glos{ALFA}{Arecibo L-Band Feed Array} \cite[alfa]. |
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| Another example, this time a custom-designed receiver and digitization unit design but duplicated many times is LOFAR system developed by Astron in the Netherlands~\cite[lofar] |
| LOFAR is an innovative radioastronomy system which uses a phased antenna array approach at an enormous scale. Thousands (around $2 \cdot 10^4$) of antennas are manufactured and deployed in the field. The centre of LOFAR system is situated in the Netherlands and peripheral antennas with the connection network extend to other European countries. |
| Another example, this time a custom-designed receiver and digitization unit design but duplicated many times is LOFAR system developed by Astron in the Netherlands~\cite[lofar]. Since thousands of antennas are used the project must use a low cost hardware due to system scale. The solution chosen in this project is based on low cost direct sampling receivers, combining RF part and digitizer in a single block. |
| |
| \midinsert |
| \clabel[lofar-antenna]{Lofar antenna configuration} |
| \picw=10cm \cinspic ./img/lofar_antenna.jpg |
| \caption/f One LOFAR LBA\glos{LBA}{Low Band Antenna} antenna element. |
| \endinsert |
| |
| Due to the size of the whole system, the LOFAR project has to use a low cost hardware. A special construction techniques were employed to keep the overall project budget at acceptable level (including for example specially designed polystyrene supporting blocks for High Band Antenna (HBA\glos{HBA}{High Band Antenna})). Many of used components are manufactured on a massive scale for other than scientific use. LBA antennas' masts are made from a standard Polyvinyl chloride (PVC\glos{PVC}{Polyvinyl chloride}) plastic waste pipes \ref[lofar-antenna]. LOFAR uses low cost direct sampling receivers. The entire project was designed by the Netherlands Institute for Radio Astronomy which produces many similarly sophisticated devices~\cite[astron-devices]. |
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| \secc Modular digitization systems |
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| Due to cost restrictions in science and astronomy instruments development, a reuse of engineering work is preferable. There is one good example of a modular digitization and data processing system - a system Collaboration for Astronomy Signal Processing and Electronics Research (CASPER\glos{CASPER}{Collaboration for Astronomy Signal Processing and Electronics Research}), that has been in development at the University of Berkeley~\cite[casper-project] since around 2005. CASPER designers and engineers noticed a remarkable lack of such hardware in radioastronomical science. Their ideas are summarised in the following paper~\cite[casper-paper]. Unfortunately, they use a proprietary connector standard and technology. They have developed a modular system based purely on Tyco Z-DOK+ connectors family. CASPER data processing board with Z-DOK connectors is shown in the Figure~\ref[casper-roach]. Z-DOK connectors have a relatively high pricing (around 40 USD)~\cite[Z-DOK-connectors], but represent high quality differential pairs connectors. However, the price of these connectors is comparable with the price of one ADC channel in the design described in this diploma thesis. |