| 8,11 → 8,11 |
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| As a consequence, there already exist effort to control the radiofrequency spectrum. As result of attempts to control the radiofrequency spectrum, the frequency allocation table was created \cite[radio-astronomy-frequency]. Radio-frequency allocation table table contains special bands allocated to radioastronomy use. However, for many reasons these bands are not clean enough to be used directly in radioastronomy observations. As a result, we cannot work in the same way as had the radioastronomers in the very beginnings of radioastronomy. Many experiments, namely Cosmic microwave background detection or pulsar detection, cannot be nowadays realised in their original forms with satisfactory results. |
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| Supporting evidence of such effect is RadioJOVE project. NASA engineers who originally created the RadioJOVE project had a great idea. The RadioJOVE project brought an opportunity for creating a publicly available, cheap radioastronomy receiver. However, they used an old-fashioned construction design which, on one hand, can operate in harsh environments like deserts, but on the other it simply did not meet the criteria that would make it possible to be used in modern civilisation, as we know it in Europe. |
| Supporting evidence of such effect is RadioJOVE project. NASA engineers who originally created the RadioJOVE project had a great idea. The RadioJOVE project brought an opportunity for creating a publicly available, cheap radioastronomy receiver. However, they used an old-fashioned construction design which, on one hand, can operate in unoccupied harsh environments like deserts, but on the other it simply did not meet the criteria that would make it possible to be used in modern civilisation, as we know it in Europe \cite[radio-jove]. |
| The source of its dysfunction is a presence of strong radiofrequency interferences. These interferences are orders of magnitude stronger than Jupiter decametric emissions, whose detection was the main aim of the RadioJOVE project. |
| From what we have already seen in the light pollution mitigation pursuit, there is only a small chance to radically improve the situation in radiofrequency spectrum. |
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| The only way to overcome this problem is to search for new methods of radioastronomy observations. New methods which allows us to work without completely clear radiofrequency bands and which allow us to see the surrounding universe even despite the existence of man-made radiofrequency interference mixture. One solution is to use already known natural radio frequency signals parameters. Natural signals usually have different signal properties than local interference. Natural objects do not have problems with transmission in bandwidths of tens of megahertz in sub 100 MHz bands. These objects are usually far away and the same signal could be received at almost half of the Earth globe without any significant differences. On the other hand, it is obvious that signals with such parameters have some drawbacks, namely in the reception power. The reception power of radioastronomical object is $1*10^9$ smaller than signal power received from a typical broadband radio transmitter. |
| The only way to overcome this problem is to search for new methods of radioastronomy observations. New methods which allows us to work without completely clear radiofrequency bands and which allow us to see the surrounding universe even despite the existence of man-made radiofrequency interference mixture. One solution is to use already known natural radio frequency signals parameters. Natural signals usually have different signal properties than local interference. Natural objects do not have problems with transmission in bandwidths of tens of megahertz in sub 100 MHz bands. These objects are usually far away and the same signal could be received at almost half of the Earth globe without any significant differences. On the other hand, it is obvious that signals with such parameters have some drawbacks, namely in the reception power. The reception power of radioastronomical object is $1 \cdot 10^9$ smaller than signal power received from a typical broadband radio transmitter. |
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| From the above mentioned facts concerning the natural radio signals we can conclude that modern requirements imposed on a radioastronomy receiver are completely different from the requirements existing back in the history. Radioastronomy is no longer limited by an access to electronic components, today it is rather limited by the everywhere presence of electronic. |
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| 92,12 → 92,24 |
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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 |
| \clabel[lofar-antenna]{Lofar antenna configuration} |
| \picw=10cm \cinspic ./img/lofar_antenna.jpg |
| \caption/f One LOFAR LBA antenna element. |
| \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 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 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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| 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 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. 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. |
| 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 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 |
| \clabel[casper-roach]{CASPER's ROACH data processing board} |
| \picw=10cm \cinspic ./img/Roach2_rev0_2xcx4mezz.jpg |
| \caption/f CASPER project ROACH-2 data processing board. White Z-DOK connectors for daughter ADC Boards can be easily seen in front. |
| \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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