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\secc Bandwidth
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\secc Bandwidth
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Historically, the bandwidth parameter in radioastronomical receivers used to be within the kilohertz range. Such a narrow bandwidth was acceptable because observations were processed directly by listening or by a paper chart intensity recorder. The chart recorder integrated the energy of a signal over a defined narrow bandwidth which was suitable for detecting the intensity variance of a microwave background. No wide-band transmitters existed in that era (except for TV\glos{TV}{Television} transmitters) and tuning to other neighbouring frequency was easy as they were mostly vacant. Parallel observations from several places were unnecessary as well because the electromagnetic conditions were nearly same at all locations.
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Historically, the bandwidth parameter in radioastronomical receivers used to be within the kilohertz range. Such a narrow bandwidth was acceptable because observations were processed directly by listening or by a paper chart intensity recorder. The chart recorder integrated the energy of a signal over a defined narrow bandwidth which was suitable for detecting the intensity variance of a microwave background. No wide-band transmitters existed in that era (except for TV\glos{TV}{Television} transmitters) and tuning to other neighbouring frequency was easy as they were mostly vacant. Parallel observations from several places were unnecessary as well because the electromagnetic conditions were nearly same at all locations.
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\sec State of the art receivers digitalization units
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\sec State of the art in receivers digitization units
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Only few digitalization systems dedicated for radioastronomy currently exists. Currently existing systems uses either custom design of whole receiver or they are constructed from commercially available components. Open-source principle attempts are very rare in radioastronomy field.
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Only a few digitization systems dedicated to radioastronomy exist currently. Today's systems use either a custom design of the whole receiver or they are constructed from commercially available components. Open-source principle attempts are very rare in the radioastronomy field.
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\secc Custom digitalization system
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\secc Custom digitization system
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Custom designs usually uses non-recurring engineering for development specific solution for observation project thus costs of this instruments are very high if developed instrument are not reproduced many times. Typical example of instrument developed and manufactured in one piece with enormous founding resources draws is Arecibo ALFA \glos{ALFA}{Arecibo L-Band Feed Array} survey multi beam feed Array.
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Custom designs usually use non-recurring engineering for the development of a specific solution for an observation project. Consequently, such instruments are very costly if the developed instrument is not reproduced many 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} survey multi beam feed Array.
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Another opposite example for custom receiver and digitalization unit design is LOFAR system developed by Astron in Netherlands \cite[lofar].
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Another opposite example for custom receiver and digitization unit design is LOFAR system developed by Astron in Netherlands \cite[lofar].
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LOFAR is innovative radioastronomy system which uses the phased antenna array approach in enormous scale and thousands (around $2 \cdot 10^4$) of antennas are manufactured an deployed on field. The centrer of LOFAR system is situated in Netherlands and peripheral antennas and connection network are extended to other European countries.
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LOFAR is innovative radioastronomy system which uses the phased antenna array approach in enormous scale and thousands (around $2 \cdot 10^4$) of antennas are manufactured an deployed on field. The centrer of LOFAR system is situated in Netherlands and peripheral antennas and connection network are extended to other European countries.
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\midinsert
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\midinsert
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\clabel[lofar-antenna]{Lofar antenna configuration}
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\clabel[lofar-antenna]{Lofar antenna configuration}
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\caption/f One LOFAR LBA \glos{LBA}{Low Band Antenna} antenna element.
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\caption/f One LOFAR LBA \glos{LBA}{Low Band Antenna} antenna element.
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\endinsert
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\endinsert
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LOFAR project must use low cost hardware due to systems scale. Special construction techniques are used to keep overall project budget at acceptable levels (specially designed polystyrene supporting blocks for HBA \glos{HBA}{High Band Antenna} antennas for example). Many of used components are manufactured in mass scale for other than scientific use LBA antennas masts are made from standard PVC \glos{PVC}{Polyvinyl chloride} plastic waste pipes and LOFAR uses low cost direct sampling receiver. Whole project has been designed by Netherlands Institute for Radio Astronomy, which produces many similarly sophisticated devices\cite[astron-devices].
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LOFAR project must use low cost hardware due to systems scale. Special construction techniques are used to keep overall project budget at acceptable levels (specially designed polystyrene supporting blocks for HBA \glos{HBA}{High Band Antenna} antennas for example). Many of used components are manufactured in mass scale for other than scientific use LBA antennas masts are made from standard PVC \glos{PVC}{Polyvinyl chloride} plastic waste pipes and LOFAR uses low cost direct sampling receiver. Whole project has been designed by Netherlands Institute for Radio Astronomy, which produces many similarly sophisticated devices\cite[astron-devices].
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\secc Modular digitalization systems
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\secc Modular digitization systems
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Due to cost restrictions in science and astronomy instruments development, an reuse of engineering work should be useful. One modular digitalization and data processing system currently exit. It is being developed at Berkley\cite[casper-project]. CASPER \glos{CASPER}{Collaboration for Astronomy Signal Processing and Electronics Research} is in development from around 2005. CASPER's designers an engineers remarkably noticed a lack of such hardware in radioastronomy science, theirs ideas are summarised in paper \cite[casper-paper]. Unfortunately they use proprietary connector standard and technology and develops modular system based purely on Tyco Z-DOK+ connectors family. CASPER data processing board with Z-DOK connectors is shown in picture \ref[casper-roach]. Z-DOK connectors have relatively high pricing (around 40 USD) \cite[Z-DOK-connectors]. Z-DOK connectors are high quality differential pairs connectors, but price of these connectors is comparable with value of one ADC channel in our design described in following part of document.
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Due to cost restrictions in science and astronomy instruments development, an reuse of engineering work should be useful. One modular digitization and data processing system currently exit. It is being developed at Berkley\cite[casper-project]. CASPER \glos{CASPER}{Collaboration for Astronomy Signal Processing and Electronics Research} is in development from around 2005. CASPER's designers an engineers remarkably noticed a lack of such hardware in radioastronomy science, theirs ideas are summarised in paper \cite[casper-paper]. Unfortunately they use proprietary connector standard and technology and develops modular system based purely on Tyco Z-DOK+ connectors family. CASPER data processing board with Z-DOK connectors is shown in picture \ref[casper-roach]. Z-DOK connectors have relatively high pricing (around 40 USD) \cite[Z-DOK-connectors]. Z-DOK connectors are high quality differential pairs connectors, but price of these connectors is comparable with value of one ADC channel in our design described in following part of document.
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\midinsert
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\midinsert
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\clabel[casper-roach]{CASPER's ROACH data processing board}
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\clabel[casper-roach]{CASPER's ROACH data processing board}
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\picw=10cm \cinspic ./img/Roach2_rev0_2xcx4mezz.jpg
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\picw=10cm \cinspic ./img/Roach2_rev0_2xcx4mezz.jpg
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\caption/f CASPER project ROACH-2 \glos{ROACH}{ Reconfigurable Open Architecture Computing Hardware (ROACH) board} data processing board. White Z-DOK connectors for daughter ADC Boards can be easily seen in front.
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\caption/f CASPER project ROACH-2 \glos{ROACH}{ Reconfigurable Open Architecture Computing Hardware (ROACH) board} data processing board. White Z-DOK connectors for daughter ADC Boards can be easily seen in front.
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\endinsert
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\endinsert
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In opposite to professional astronomers which uses proprietary digitalization units, amateur radioastronomers currently uses multichannel sound cards \cite[amateur-fringes] or self designed digitalisation units. Devices constructed by amateurs are usually non reproducible \cite[amateur-sdr] . It is evident that current radioastronomy lacks of proper hardware which could be used on both communities - professionals and amateurs. Optimal solution for this situation should be open-source hardware.
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In opposite to professional astronomers which uses proprietary digitization units, amateur radioastronomers currently uses multichannel sound cards \cite[amateur-fringes] or self designed digitalisation units. Devices constructed by amateurs are usually non reproducible \cite[amateur-sdr] . It is evident that current radioastronomy lacks of proper hardware which could be used on both communities - professionals and amateurs. Optimal solution for this situation should be open-source hardware.
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