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\caption/t Standard bit depths of ADC and its theoretical dynamic range.
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\caption/t Standard bit depths of ADC and its theoretical dynamic range.
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\endinsert
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\endinsert
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% dopsat cast o minimalnim dynamickem rozsahu ADC.
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% dopsat cast o minimalnim dynamickem rozsahu ADC.
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If we look at actual spectrum occupancy in Europe (measured in power spectral density) we see that signal dynamic range in spectra
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\url{http://observatory.microsoftspectrum.com}
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easily reaches 80+ dB above natural noise levels. If we don't want to deal with receiver saturation or poor sensitivity we need a receiver and digitalization unit which has comparable dynamical range of with received signals. This imply use of least 14 bit ADC without any spare of range.
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\secc Bandwidth
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\secc Bandwidth
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Historically, the parameter of bandwidth in radioastronomical receiver used to be within the kilohertz range. Small bandwidth was acceptable because observations were processed directly by listening or by paper chart intensity recorder. Chart recorder integrated energy of signal over defined small bandwidth which was suitable for detecting the intensity variance of microwave background. No wideband transmitters existed in that era (except for TV 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 parameter of bandwidth in radioastronomical receiver used to be within the kilohertz range. Small bandwidth was acceptable because observations were processed directly by listening or by paper chart intensity recorder. Chart recorder integrated energy of signal over defined small bandwidth which was suitable for detecting the intensity variance of microwave background. No wideband transmitters existed in that era (except for TV 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 Current status of receivers digitalization units
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% dopsat navaznost na aktualne pouzivane digitalizacni jednotky
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% dopsat navaznost na aktualne pouzivane digitalizacni jednotky
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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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\secc Coustom digitalization system
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Coustom 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.
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The system requires proper handling of huge amounts of data.
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The system requires proper handling of huge amounts of data.
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Professional astronomers use proprietary digitalisation units \url{http://arxiv.org/abs/1305.3550} or by multichannel sound cadrd on amateur levels \url{http://fringes.org/}
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Professional astronomers use proprietary digitalization units \url{http://arxiv.org/abs/1305.3550} or by multichannel sound cadrd on amateur levels \url{http://fringes.org/}
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ASTRON ADCs
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http://www.astron.nl/other/desp/competences_DesApp.htm
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\secc Modular digitalization systems
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One modular digitalization system currently exit. It is beaing developed at Berkley
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\url{https://casper.berkeley.edu/wiki/Main_Page}
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Z-DOK connectors have relatively high pricing around 40 USD http://www.digikey.com/product-detail/en/6367550-5/6367550-5-ND/2259130
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This price is comparable with value of one ADC channel in our design described in following part of document.
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Mudular radioastronomy hardware: https://casper.berkeley.edu/papers/200509URSI.pdf
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